Electric-Field Contact-less Sensing Systemcache.freescale.com/files/sensors/doc/ref_manual/APPEFIELDRM.pdf · 2.3 Principle of Operation ... The Electric-Field Contact-less Sensing

MC33794 (Electric-Field Sensing IC)

freescale.com

APPEFIELDRM Rev. 009/2006

Designer Reference ManualElectric-Field Contact-less Sensing System

Electric-Field Contact-less Sensing System, Rev. 0

2 Freescale Semiconductor

Electric-Field Contact-less Sensing SystemDesigner Reference Manual

by: Jozef Prokopovic Freescale Czech Systems Laboratories Roznov pod Radhostem, Czech Republic

To provide the most up-to-date information, the revision of our documents on the World Wide Web will be the most current. Your printed copy may be an earlier revision. To verify that you have the latest information available, refer to http://www.freescale.com.The following revision history table summarizes changes contained in this document. For your convenience, the page number designators have been linked to the appropriate location.

Revision History

Date RevisionLevel Description Page

Number(s)

09/2006 0 Initial release 52

http://www.freescale.com

Table of Contents

Chapter 1 Introduction

1.1 Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.3 About this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Chapter 2 Theory

2.1 Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.2 E-Field Sensing: An Alternative Solution to Control Panel Applications . . . . . . . . . . . . . . . . . . 112.3 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Chapter 3 System Concept

3.1 Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.2 System Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.3 Application Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Chapter 4 Hardware

4.1 Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.2 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.3 Application schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.4 Hardware design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.4.1 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.4.2 E-Field Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.4.3 Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.4.4 Serial Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.4.5 Op-Amp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.4.6 MSDI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.4.7 H-Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.4.8 Buzzer circuitry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.4.9 Jumpers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.4.10 Connectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Chapter 5 Software

5.1 Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245.2 Software Design Consideration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24


Freescale Semiconductor 3

5.3 Main Data Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245.4 Firmware Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315.5 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355.6 FreeMASTER Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Chapter 6 Application Setup

6.1 Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376.2 Setting Up the Demo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376.3 Power Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386.4 Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386.5 Modes of E-Field Demonstrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386.5.1 Touch Pad (Keyboard) Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.5.2 Slider Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406.5.3 Water Pump Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406.5.4 Water Slider Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416.6 Demo System Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416.7 Starting the Demo System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426.7.1 Step 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426.7.2 Step 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436.7.3 Step 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446.8 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Appendix A. E-Field Contactless Sensing Demonstrator

Schematics

Appendix B. E-Field Contactless Sensing Demonstrator

Bill of Material





List of Figures

Figure 1-1 System Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 1-2 E-Field Contactless Sensing Demonstrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Figure 2-1 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Figure 3-1 Water Column. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Figure 3-2 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Figure 3-3 Minimizing fringing fields with SHIELD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Figure 4-1 SPI communication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Figure 4-2 H-Bridge circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Figure 4-3 Default jumpers configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Figure 4-4 Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Figure 5-1 State Diagram - General Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Figure 5-2 Main Data Flow Chart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Figure 5-3 Touch Pad Mode Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Figure 5-4 Slider Mode Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Figure 5-5 Water Pump Mode Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Figure 5-6 Water Slider Mode Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Figure 5-7 TIM Overflow Interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Figure 5-8 FreeMASTER Software Control Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Figure 6-1 E-Field (Touch Pad Board, Water Level Board) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Figure 6-2 E-Field demo (TPB connected with WLB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Figure 6-3 Mode Selection Button . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Figure 6-4 Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Figure 6-5 Slider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Figure 6-6 Pump Up (Down) Button. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Figure 6-7 Water Slider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Figure 6-8 Main Window of FreeMASTER Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Figure 6-9 Options Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Figure 6-10 Open Project Window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Figure A-1 Schematics “A” of Touch Pad Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-2Figure A-2 Schematic “B“ of Touch Pad Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-3Figure A-3 Schematic of Water Level Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-4



List of TablesTable 4-1 Electrode Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Table 4-2 Truth Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Table 4-3 Jumpers Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Table 4-4 J3 (J1) connector of TPB (WLB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Table 4-5 J4 (J2) connector of TPB (WLB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Table 4-6 J2 connector of TPB (DB9 female) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Table 5-1 Main, Initialization, FreeMASTER Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Table 5-2 Calibrate Electrodes, Read Values, Read Electrode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Table 5-3 Read Delta, Verify Electrodes, Display Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Table 5-4 Bar Graph, Water Bar Graph, Water Slider Graph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Table 5-5 Rotate Up, Rotate Down, Stop Rotate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Table 5-6 Beep On, Beep Off, Auto Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Table 5-7 SendSPI, SendpSPI, Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Table 5-8 GetTick, Beeper, Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Table 5-9 Slider, Water Slider, Measure Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Table 5-10 Water Level, Verify Key, Verify Mode Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Chapter 1 Introduction

1.1 Contents

1.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.3 About this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.2 Introduction

This reference manual describes the design and features of an Electric-Field Contact-less Sensing System based on Freescale’s MC33794 (Electronic Field Imaging Device).

The MC33794 is intended for cost-sensitive applications where non-contact sensing of objects is desired. When connected to external electrodes, an electric field is created. The MC33794 is intended to detect objects in this electric field. The IC generates a low-frequency sine wave, adjustable by using an external resistor, and is optimized for 120 kHz. The sine wave has very low harmonic content to reduce harmonic interference.

The MC33794 also contains support circuits for a microcontroller unit (MCU) to allow the construction of a two-chip E-field system.

MC33794 features

• Supports up to nine Electrodes and two References or Electrodes

• Shield Driver for Driving Remote Electrodes Through Coaxial Cables

• +5.0 VDC Regulator to Power External Circuit

• ISO-9141 Physical Layer Interface

• Lamp Driver Output

• Watchdog and Power-ON Reset Timer

• Critical Internal Nodes Scaled and Selectable for Measurement

• High-Purity Sine Wave Generator Tunable with External Resistor

• Response Time Tunable with External Capacitor



Introduction

Typical Applications

• Appliance Control Panels and Touch Sensors

• Linear and Rotational Sliders

• Spill Over Flow Sensing Measurement

• Refrigeration Frost Sensing

• Industrial Control and Safety Systems Security

• Proximity Detection

• Touch Screens

• Liquid Level Sensing

The Electric-Field Contact-less Sensing System is based on this MC33794 device. This application is controlled by a low cost 8-bit microcontroller, the MC68HC908QB8. This E-Field demonstrator detects human touch through glass and measures the level of water in a water column. An illustration of the system configuration is shown in Figure 1-1 System Configuration.

The Electric-Field Contact-less Sensing System has the following features:

• Detecting human touch (Touchpad, Slider) and water level detection (Water pump, Water slider) using Freescale MC33794 E-Field sensor

• Freescale MC68HC908QB8 8-bit microcontroller

• Freescale MC33993 MSDI (Multiple Switch Detection Interface) – driving LEDs– interfaces directly with the microcontroller using SPI protocol

• Freescale MC33886 H-Bridge used as a water pump motor driver

• Connection with PC via RS232

• Option of installing a Dual Op-Amp to amplify weak E-Field signals

• 7-segment numeric LED display, LED Bar-Graph

• Input supply voltage +12V DC / 2A

• Audio Buzzer

Figure 1-2 Electric-Field Contact-less Sensing System shows the board layout with description of the components.



About this Manual

Figure 1-1. System Configuration

1.3 About this Manual

Key information can be located at the following location in this manual:

• Setup instructions are found in Chapter 6 Application Setup

• Pin-by-pin descriptions are contained in Tables 4-4 to 4-6

• For those interested in the reference design aspects of the board’s circuitry, a description is provided in Chapter 5 Software



About this Manual

Figure 1-2. Electric-Field Contact-less Sensing System



Chapter 2 Theory

2.1 Contents

2.2 E-Field Sensing: An Alternative Solution to Control Panel Applications . . 112.3 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2 E-Field Sensing: An Alternative Solution to Control Panel Applications

Human touch can be a useful tool. Control panels, appliances, heavy machinery, toys, lighting controls, and anything that has a mechanical switch or push button requires some sort of human interaction to operate. Traditionally, push buttons are made from mechanical switches and/or multi-layer resistive touch pads that can deteriorate and become less dependable over time. This is because most of these switches require physical displacement and pressure, and are susceptible to wear-out, contact bounce, corrosion and arcing.

The MC34940/MC33794 Electric Field Imaging devices from Freescale offers an alternative to mechanical push buttons for control panel applications. The MC34940/MC33794 Integrated Circuits (IC) contain the circuitry necessary to generate a low level electric field and measure the field loading caused by objects moving into or out of the field. It is ideal for applications that require non-contact sensing, proximity detection, and three-dimensional e-field imaging. The ICs integrate support for a microcontroller and seven to nine electrodes, which can be used independently to determine the size or location of an object in a weak electric field.

With the MC34940/MC33794, membrane switches and resistive touch pads can be replaced by an array of touch pads consisting of conductive electrodes embedded beneath an insulating surface. Since it has the capability of sensing touch and proximity through the insulating sur-face, without direct electrical contact with the electrode metal, problems of wear, contamination, and corrosion are eliminated.

Furthermore, one of the MC34940/MC33794 key features that surpasses simple capacitive-based sensors is its on-board shield driver. Touch pads do not have to be combined and located in one centralized location. With proper shielding, coaxial cables or PCB layers can be used to connect remote touch pads up to a few meters away, while obtaining measurements as accurately as if the touch pads were directly connected to the IC. The MC34940/MC33794 does this by driving a signal on the shield of the coax, or a PCB trace, which closely follows the signal conductor voltage. The current which flows through the electric field between two conductors is proportional to the voltage difference between them. With little or no voltage difference, there is little or no current flow between the electrode conductor and the shielding trace or coax shield.



Principle of Operation

2.3 Principle of Operation

The MC33794 is intended for use in detecting objects using an electric field. The IC generates a low radio frequency sine wave. The frequency is set by an external resistor and is optimized for 120 kHz. The sine wave has very low harmonic content to reduce potential interference at higher harmonically related frequencies. The internal generator produces a nominal 5.0 V peak-to-peak output that is passed through an internal resistor of about 22 kΩ. An internal multiplexer routes the signal to one of 11 terminals under the control of the ABCD input terminals. A receiver multiplexer simultaneously connected to the selected electrode routes its signal to a detector, which converts the sine wave to a DC level. This DC level is filtered by an external capacitor and is multiplied and offset to increase sensitivity. All of the unselected electrode outputs are grounded by the device. The amplitude and phase of the sinusoidal wave at the electrode are affected by objects in proximity. A “capacitor” is formed between the driving electrode and the object, each forming a “plate” that holds the electric charge. The voltage measured is an inverse function of the capacitance between the electrode being measured, the surrounding electrodes, and other objects in the electric field surrounding that electrode. Increasing capacitance results in decreasing voltage. The value of the series resistor (22kΩ) was chosen to provide a near linear relationship at 120 kHz over a range of 10pF to 70pF. While exploring applications using E-Field products, it is always useful to approach the problem using the capacitor model.

Figure 2-1. Principle of Operation



Chapter 3 System Concept

3.1 Contents

3.2 System Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 System Specification

The main goal of this demo board is to present features of the MC33794 E-Field sensor product. It is an application dedicated to sense human touch and liquid level. Every button and slider senses human touch and proximity. Water level is measured in the water column by copper electrodes fixed on the column from the outside.

Figure 3-1. Water Column

Non-Metallic Container(Water Column)

Conductive Bands(Copper Electrodes)

Liquid(Water)

E-Field

Non-Metallic Container(Water Column)

Conductive Bands(Copper Electrodes)

Liquid(Water)

E-Field



Application Description

This demo consists of two main boards: Touch Pad Board and Water Level Board. Interfacing is implemented through connectors. There is also the option of installing a Dual Op-Amp to amplify weak E-Field signals if required.

The E-Field demonstrator can work in 4 modes: Touch Pad, Slider, Water Pump and Water Slider.

A mode selection electrode is used to switch the demo to another mode.

The FreeMASTER GUI is used to bring a visual demonstration of electrode behavior during the sensing of human touch or water level.

3.3 Application Description

Figure 3-2 shows a block diagram of the application.

Figure 3-2. Block Diagram

The main application consists of Freescale ICs such as

• MC33794 Electric Field Sensing Device

• MC68HC908QB8 8-bit Microcontroller (8K FLASH)

HC908QB88-bit MCU

MC33794E-field

Electrode select (A,B,C,D)

LEVEL

E-fieldelectrodes

PWM/direction

SPI

+5V Vdd

+12Vpowersupply

FreeMASTERRS232 PC connection

MMC33886H-bridge

Water pump motor

Shield

MC33993MSDI

. . . . . .

LED’s Display

Buzzer

Dual Op-Amp

FreeMASTER

SW for SCI

HC908QB88-bit MCU

MC33794E-field

Electrode select (A,B,C,D)

LEVEL

E-fieldelectrodes

PWM/direction

SPI

+5V Vdd

+12Vpowersupply

FreeMASTERRS232 PC connection

MMC33886H-bridge

Water pump motor

Shield

MC33993MSDI

. . . . . .

MC33993MSDI

. . . . . .

LED’s Display

Buzzer

Dual Op-Amp

FreeMASTER

SW for SCI



Application Description

• MC33993 Multiple Switch Detection Interface

• MC33886 H-Bridge

MC33794 is intended for sensing the electric field generated near the electrodes. This application uses nine electrodes (buttons and conductive bands) and one reference electrode (mode selection button). A second reference electrode pin is connected through a capacitor to the ground. Just one of these electrodes can be selected at a time for measurement. All of the other unselected electrodes are grounded by an internal switch, apart from the reference electrodes. Fringing fields were reduced by placing a copper layer connected to the SHIELD pin at the bottom and around the electrodes at the top of the PCB (Figure 3-3).

Figure 3-3. Minimizing fringing fields with SHIELD

The detected, amplified and offset representation of the signal voltage on the selected electrode is connected through the LEVEL pin to the MCU A/D convertor. Pins A, B, C, D are 5V logic pins controlled from the MCU, intended to select appropriate electrodes. The converted value is stored, read and displayed by the FreeMASTER SW using serial communication (RS232).

The application is powered by +12V DC. The power supply of +5V DC for the MCU and other devices is provided by the MC33794’s +5.0V DC internal voltage regulator (Vcc).

The MSDI device (MC33993) drives the LEDs and the 7 segment display and is controlled by SPI commands from the MCU through SPI communication protocol. The LEDs and display are connected directly to the MSDI SG or SP pins.

The MC33886 is a monolithic H-Bridge. In this application it is used as a controller of the water pump DC motor. The MCU generates 6.25kHz PWM signal to drive the MC33886. The PWM duty cycle is decreased or increased by the MCU to provide the desired speed for pumping the water.

In addition, a visualization of several variables via computer has been implemented. FreeMAS-TER software is used for the purpose of graphical visualization, communicated via SCI protocol. The FreeMASTER SCI software is also implemented in the MCU to allow communication between the application and the PC. The communication speed is 57600Baud.

Button

Copper Plates connected to SHIELD pin

Button

Copper Plates connected to SHIELD pin



Chapter 4 Hardware

4.1 Contents

4.2 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.3 Application schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.4 Hardware design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.4.1 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.4.2 E-Field Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.4.3 Microcontroller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.4.4 Serial Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.4.5 Op-Amp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.4.6 MSDI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.4.7 H-Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.4.8 Buzzer circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.4.9 Jumpers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.4.10 Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.2 System Overview

The demo consists of two boards - TOUCH PAD BOARD (TPB) and WATER LEVEL BOARD (WLB). The boards are attached to each other. Refer to Figure 6-1 and Figure 6-2.

The TPB contains:

• E-Field chip (MC33794)

• MCU (HC908QB8)

• RS232 connection (MAX202, DB9 female)

• Dual Op-Amp (LM358 - optional)

• Power supply jack (+12 VDC)

• Buzzer circuitry

• Buttons (keyboard, slider, mode selection button)

The WLB contains:

• Water column with copper electrodes

• H-Bridge (MC33886)

• MSDI (MC33993)



Application schematics

• Water slider

• LED Bar, 7 segment LED Display

For a block diagram, refer to Figure 3-2.

4.3 Application schematics

Figure A-1and Figure A-2 are schematics of the Touch Pad Board. Figure A-3 is a schematic of the Water Level Board.

4.4 Hardware design considerations

4.4.1 Power Supply

The board is powered by a +12 VDC external supply through jack J1 on the Touch Pad Board. An internal voltage regulator in the E-Field IC provides +5.0V DC for remaining circuits.

4.4.2 E-Field Sensor

MC33794 is powered by a +12 VDC from an external power supply. The +12V DC applied to the VPWR pin is converted into the regulated voltages needed to operate the part. It is also converted into +5.0V DC to power the MCU and external devices.

The level detected from output pin LEVEL is connected directly to the MCU A/D convertor, optionally through the Dual Op-Amplifier.

A specific electrode is selected by the A, B, C, D pins Table 4-1, which are controlled from the MCU.

Table 4-1. Electrode Selection

PIN/SIGNAL D C B A

Source(internal) 0 0 0 0

E1 0 0 0 1

E2 0 0 1 0

E3 0 0 1 1

E4 0 1 0 0

E5 0 1 0 1

E6 0 1 1 0

E7 0 1 1 1

E8 1 0 0 0

E9 1 0 0 1

REF_A 1 0 1 0

REF_B 1 0 1 1

Internal OSC 1 1 0 0

Internal OSC after 22kΩ 1 1 0 1

Internal Ground 1 1 1 0

Reserved 1 1 1 1



Hardware design considerations

Resistor R2 determines the operating frequency of the oscillator. R2 = 39kΩ to provide an operating frequency = 120kHz.

Electrodes (E1- E9) are used as single button electrodes on the Touch Pad Board. The slider on the Touch Pad Board is made from electrodes E6 and E7. The slider on the Water Level Board is made from E8 and E9. Five conductive bands on the water column are connected as electrodes E1- E5. The SHIELD pin is connected to the shield copper layer and is also tied to connector J3 for Water Level Board purposes. REF_A pin is used as a single (Mode Selection) electrode to switch between all modes. To avoid REF_B pin floating, this pin is connected through C19 to ground.

The VCC pin provides +5.0V DC for the remaining circuits. C4 and C5 are connected to this pin to provide a stabilized voltage.

4.4.3 Microcontroller

The system is based on an MC68HC908QB8, 8-bit, low cost microcontroller, powered by a +5V DC from the E-Field sensor. The MCU selects each specific E-Field channel, reads output from the E-Field sensor and takes appropriate action. It also sends commands to the MSDI to drive LEDs, toggle the Buzzer ON or OFF, handle interfacing with the H-Bridge (driving the water pump), and performs serial communication with the implemented FreeMASTER software via RS232.

As soon as the MCU is programmed with the serial bootloader, the MCU memory can be modified in-circuit via the serial port (see AN2295/D Developer’s Serial Bootloader for M68HC08 and HCS08 MCUs).

Detected levels are fed from the E-Field to the MCU A/D channel. This A/D converter works in 10-bit resolution mode.

The PWM output from the microcontroller, combined with direction signals, drives the water pump motor through the H-Bridge.

No external crystal or oscillator is required, as the MCU runs on an internal oscillator.

Pins PTA 0, PTA1, PTA4, PTA5 select each specific E-Field channel (see Table 4-1) PTA0 = A, PTA1 = B, PTA4 = C, PTA5 = D.

4.4.4 Serial Communication

Serial communication uses the ESCI module of the QB8 microcontroller, a MAX202 and a DB9 connector. The E-Field demonstrator application implements software serial communication and FreeMASTER (formerly known as PC Master) code in order to demonstrate the sensing process. Serial communication is fully controlled by the implemented FreeMASTER software. The details are given in the separate Freescale Application notes (see AN2395 - PC Master Software Usage and AN2471 - PC Master Software Communication Protocol Specification).




4.4.5 Op-Amp

The Touch Pad Board includes footprints for Op-Amp components. This amplifier was considered to provide higher sensitivity to the signal read by the MCU A/D convertor. Measured results have shown that this Op-Amp is not necessary in this application.

4.4.6 MSDI

The 33993 Multiple Switch Detection Interface is designed to detect the closing and opening of up to 22 switch contacts. The switch status, either open or closed, is transferred to the microprocessor unit (MCU) through a serial peripheral interface (SPI).

Figure 4-1. SPI communication

In this particular application, the MSDI drives LEDs D1- D14 and the seven segment display DIS1. D1 - D14 are connected to SG pins and DIS1 is connected to SP pins (SP pins are switched to the battery, SG pins are switched to the ground). In this application we use the internal configurable current sources. 2mA current sources are used for the LEDs, and 16mA current sources are used for DIS1.

The MSDI communicates with the MCU using just a three wire (MOSI, SCLK and CSB) SPI because no feedback from the MSDI is required (Figure 4-1).

4.4.7 H-Bridge

Freescale’s MC33886 is a monolithic H-Bridge ideal for DC-motor and bi-directional thrust solenoid control. The 33886 is able to control continuous inductive DC load currents up to 5.0A. The water pump motor used in the E-Field demo is a 3.0A load. Output loads can be pulse width modulated (PWM-ed) at frequencies up to 10kHz.

The H-Bridge can operate in several modes but we are using just two of them (Table 4-2):

• Forward

• Reverse

HC08QB8 SPI master

MOSI

SCLK

CSB

SPI Shift register

MC33993 MSDI SPI slave

MOSI

SCLK

CSB

SPI Shift register

HC08QB8 SPI master

MOSI

SCLK

CSB

SPI Shift register

MC33993 MSDI SPI slave

MOSI

SCLK

CSB

SPI Shift register




The DC motor is connected through the OUT1 and OUT2 terminals to the internal power MOSFET H-Bridge of the IC. IN1(direction) and IN2 (PWM signal) are input control terminals used to control OUT1 and OUT2 (see Figure 4-2).

Figure 4-2. H-Bridge circuitry

4.4.8 Buzzer circuitry

The buzzer is controlled directly by a GPIO pin of the MCU (PTB7). A MOSFET transistor is used to switch the buzzer ON or OFF.

4.4.9 Jumpers

The configuration jumpers in the E-Field demonstrator are JP1 and JP2.

JP1 selects between two values of LP_CAP (Low-Pass Filter Capacitor), 10nF or 1nF. A capacitor on this pin forms a low pass filter with the internal series resistance from the detector to this pin. This pin can be used to determine the detected level before amplification or offset is

Table 4-2. Truth Table

Device StateInput Conditions

Fault Status Flag

Output States

D1 D2 IN1 IN2 FS OUT1 OUT2

Forward L H H L H H L

Reverse L H L H H L H

HC08QB8MC33886H-Bridge

DCmotor

OUT1

OUT2FSD1D2+5V

IN1

IN2TCH2

PTA3direction

PWM (6.25kHz)

HC08QB8MC33886H-BridgeMC33886H-Bridge

DCmotorDC

motor

OUT1

OUT2FSD1D2+5V

IN1

IN2TCH2

PTA3direction

PWM (6.25kHz)




applied. A 10 nF capacitor connected to this pin is recommended. More capacitance will increase the response time unnecessarily.

JP2 selects whether the input to the MCU A/D convertor is fed directly from the MC33794 output pin LEVEL or if the output signal is first amplified by the op-amp. The op-amp is not populated in this revision of the board, therefore JP2 in position 2-3 has no meaning.

Figure 4-3. Default jumpers configuration

4.4.10 Connectors

The Touch Pad Board (TPB) and Water Level Board (WLB) are connected together with connectors J3, J4 on the TPB (Figure A-1, Figure A-2), and J1, J2 on the WLB (Figure A-3). J3 on the TPB matches up with J1 on the WLB. J4 on the TPB matches up with J2 on the WLB.

Electrode signals and Shield signal are grouped together on the J3 connector of the TPB and the J1 connector of the WLB. SPI signals, H-Bridge control signals, power supply and GND are

Table 4-3. Jumpers Configuration

Jumper Position Description

JP1 1-2C7 (1nF) connected to

LP_CAP pin

JP1 2-3C8 (10nF) connected to

LP_CAP pindefault

JP2 1-2LEVEL pin connected

directly to MCUdefault

JP2 2-3LEVEL pin connected

through Op-Amp to MCU

1 3

1

2JP1

3 2

JP2

1 3

1

2JP1

3 2

JP2




grouped on the J4 connector of the TPB and on the J2 connector of the WLB. Pin assignments are shown in Figure 4-4 Connectors.

Figure 4-4. Connectors

1 23 45 67 89 10

14131211

19

15 161817

212022

23 242625

Shield

ShieldShield

ShieldShield

Shield

Shield

Electrode 9

Electrode 5Electrode 8



J3 connector of TPBJ1 connector of WLB

1 23 45 67 89 10

14131211

19

15 161817

212022

23 242625

GND

J4 connector of TPBJ2 connector of WLB

MOSICSB

+5V

PTA3PTB6/TCH2

SCLK

+5V

+12V

1

2

3

4

5

6

7

8

9GND

RXD

TXD

J2 connector of TPBDB9 female




Pin descriptions are listed in Table 4-4, Table 4-5, Table 4-6.

Table 4-4. J3 (J1) connector of TPB (WLB)

Pin#

Signal Name Description

1-6, 8, 10, 12, 14, 16, 18, 20-26

SHIELDShield Driver. These pins are connected to a shield plate to

cancel fringing fields.

7, 9, 11, 13, 15, 17

Electrode 9,....., Electrode 1

Electrode Connections. These are the electrode terminals.

Table 4-5. J4 (J2) connector of TPB (WLB)

Pin#


1 SCLK Serial Clock. SPI control clock input pin.

3 MOSI SPI Slave In. SPI control data input pin from MCU to 33993

5 CSBChip Select. SPI control chip selects the input pin from MCU to 33993. Logic 0 allows data to be transferred in.

7 PTA3Direction pin. Determines direction of the DC motor.

(MCU -> H-Bridge)

9 PTB6/TCH2PWM signal pin. Determines speed of the DC motor.

(MCU -> H-Bridge)

11, 13 +5V +5.0V DC power supply

15, 17, 19, 21, 23, 25

+12V +12.0V DC power supply

2, 4, 6, 8, 10, 12, 14, 16, 18, 20,

22, 24, 26GND Ground

Table 4-6. J2 connector of TPB (DB9 female)

Pin#


2 TXD Transmit SCI Data

3 RXD Receive SCI Data

5 GND Ground

1, 4, 6, 7, 8, 9 NC Not connected



Chapter 5 Software

5.1 Contents

5.2 Software Design Consideration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245.3 Main Data Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245.4 Firmware Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315.5 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355.6 FreeMASTER Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.2 Software Design Consideration

Electrode value reading is done by the MCU, by selecting the appropriate channel lines (Table 4-1) and then reading the value on the MCU A/D module. Differences from calibrated values represent changes in the electrode field, meaning the electrode might have been influenced by human touch or water level presence.

The application gives feedback to the user through the on board display, LEDs and a buzzer. The board can also be connected to the PC via an SCI port. On board Display and LEDs are managed using an MSDI device (4.4.6). SCI communication is handled by the implemented FreeMASTER Software.

5.3 Main Data Flow Chart

The general software diagram incorporates the main routine (Main) entered from reset and the interrupt service routines. The general overview of the control algorithm is described in Figure 5-1.

The main routine initializes the MCU, MSDI device and the FreeMASTER software, starts the TIM counter, enable interrupts, performs a delay to let things settle, reads the calibration values, tests the Buzzer and then it enters an endless loop. The endless loop contains four working modules (Touch pad, Slider, Water Pump, Water Slider). The Mode key is tested in every cycle and according to its state, the working modes are switched inside the infinite loop.

Working modes are described in flow charts from Figure 5-3 to Figure 5-6.



Main Data Flow Chart

Figure 5-1. State Diagram - General Overview

The SCI interrupt services the FreeMASTER communications between the PC and MCU. The Timer Overflow interrupt handles the time delay for the Buzzer (refer to page 35).

Reset

Initialization

Main loopE-Field service

SCI interrupt

done

done

FreeMASTER

Timer Overflow interrupt

INTERRUPTS

Handle delay for Buzzer




Figure 5-2. Main Data Flow Chart

RESET

Initialization

Start TIM counterTSTOP bit = 0

FreeMASTER initialization

Enable Interrupts

300ms delaydisplay show (0-F)

turn off LED Bar 1000ms delay

Read and store calibration electrode values

Buzzer test

Touch Pad modeSlider mode

Water Pump modeWater Slider mode

Touch Pad mode

mode key pressed

Slider mode

yes

no

mode key pressed no

yes

Water Pump mode

mode key pressed no

yes

Water Pump mode

mode key pressed no

yes




Figure 5-3. Touch Pad Mode Flow Chart

Touch Pad Mode

Delete 7 segment display

Turn on Touch pad LED

mode key pressedyes

Read electrode values

no

Turn on Buzzer for 10mS

Read delta values

Switch to Slider ModeFind the three highest

Autocalibration

Check pressed key

Display pressed keyShow maximum delta value

delta values




Figure 5-4. Slider Mode Flow Chart

Slider Mode

Delete 7 segment display

Turn on Slider LED

mode key pressedyes


no

Turn on Buzzer for 10mS

Read delta values

Switch to Water Pump ModeFind the three highest

Autocalibration

Detect slider touch and display finger position on the

LED Bar

delta values




Figure 5-5. Water Pump Mode Flow Chart

Water Pump Mode

Delete 7 segment displayTurn on Water Pump LED

mode key pressedyes


noTurn on Buzzer for 10mS

Read delta values

Switch to Water Slider Mode

Find the three highest

Check pressed key

delta_values7 = pump up buttondelta_values8 = pump down button

delta_values7 > PUMP_THRESHOLDno

yesdelta_values0 = highest conductive band

&&delta_values0 <DELTA_MAX

Stop Motoryes

noPump water up

pump up button pressed

delta_values8>

PUMP_THRESHOLD

delta_values7 - delta_values8>

DELTA_NEIGHBOUR

yes

no

Stop Motor

Pump water out

pump down button pressed

Display the actual water level

pump up or pump down

button pressed

on the LED Bar

delta values, Autocalibration




Figure 5-6. Water Slider Mode Flow Chart

Water Slider Mode

Delete 7 segment displayTurn on Water Slider LED

mode key pressedyes


noTurn on Buzzer for 10mS

Read delta values

Switch to Touch Pad Mode

Find the three highest

required_level > actual_level

no

yes

&&delta_values0 < DELTA_MAX

yes

no

required_level ≠ 100

yes

no

Stop Motor

Pump water out

Display the actual water level

Get required and actual levels

slider touched

required_level < actual_level&&

delta_values4 > MIN_LEVEL

tmp_level > actual_level&&

delta_values0 < DELTA_MAX

Pump water up Pump water up

yes

no

tmp_level < actual_level&&

delta_values4 > MIN_LEVEL

Pump water out

yes

Stop Motor

no

slider position > measured level

delta_values0 - highest conductive banddelta_values4 - lowest conductive band

slider position < measured level

required position > measured level

required position > measured level

delta values, Autocalibration

on the LED Bar



Firmware Functional Description

5.4 Firmware Functional Description

Table 5-1. Main, Initialization, FreeMASTER Initialization

Table 5-2. Calibrate Electrodes, Read Values, Read Electrode

Table 5-3. Read Delta, Verify Electrodes, Display Data

Module: main.c main.c freemaster_protocol.c

Function: main InitPorts FMSTR_Init

Syntax: void main(void) void InitPorts(void) void FMSTR_Init(void)

Parameters: none none none

Return: none none none

Description:

Initializes MCU, MSDI and FreeMASTER. Gets the calibration values, scans electrodes, and takes appropriate action.

Initializes MCU (oscillator, GPIO, Timer, ADC, SPI, SCI) and external MSDI device.

FreeMASTER driver initialization (initialize communication and start listening for commands).

Module: main.c main.c main.c

Function: CalibrateElectrodes ReadValues ReadElectrode

Syntax: void CalibrateElectrodes(void) void ReadValues(void)void ReadElectrode(unsigned char)

Parameters: none none channel (MC33794 channel)


Description:

Reads each electrode value (takes 16 samples and averages the result) and stores it in the electrode’s calibration register.

Scans all electrodes from 1 to NUMBER_OF_ELECTRODES using function ReadElectrode().

Reads the selected channel and places the result into RAM.


Function: ReadDelta VerifyElectrodes DisplayData

Syntax: void ReadDelta(void) void VerifyElectrodes(void) void DisplayData(unsigned char)

Parameters: none none pressed_key (pressed button)


Description:

Measures the difference between the current electrode value and the calibration value and stores it as the delta value in RAM. Measures the total sum of delta values.

Finds the three highest delta values .

Displays the pressed key on the 7 segment display using MSDI and a beep is generated when a button is pressed.




Table 5-4. Bar Graph, Water Bar Graph, Water Slider Graph

Table 5-5. Rotate Up, Rotate Down, Stop Rotate

Table 5-6. Beep On, Beep Off, Auto Calibration


Function: BarGraph WaterBarGraph WaterSliderGraph

Syntax: void BarGraph(unsigned char)void WaterBarGraph(unsigned int)

void WaterBarGraph(unsigned int)

Parameters: led (maximum delta value)wbar_delta (total sum of delta values)

wslider_delta


Description:Routine to handle the LED Bar in Touch Pad mode. The maximum delta value is displayed.

Routine to handle the LED Bar in Water Pump mode. Displays wbar_delta.

Routine to handle the LED Bar in Water Slider mode. Displays wslider_delta.


Function: RotateUp RotateDown StopRotate

Syntax: void RotateUp(void) void RotateDown(unsigned char) void StopRotate(void)

Parameters: none speed none


Description:

Generates PWM signal for the H-Bridge to drive the DC motor (pumps water into the water tube).

Generates PWM signal for the H-Bridge to drive the DC motor (pumps water out of the water tube).

Stops the DC motor.


Function: BeepOn BeepOff AutoCalibration

Syntax: void BeepOn(void) void BeepOff(void) void AutoCalibration(void)



Description: BeepOn - turn on the buzzer (PTB_PTB7 = 1)

BeepOff - turn off the buzzer (PTB_PTB7 = 0)

Tests conditions and calls the CalibrateElectrodes() function when needed.




Table 5-7. SendSPI, SendpSPI, Delay

Table 5-8. GetTick, Beeper, Count

Table 5-9. Slider, Water Slider, Measure Water

Module: communications.c communications.c delay.c

Function: SendSPI SendpSPI Delay

Syntax: void SendSPI(void) void SendpSPI(char *) void Delay(unsigned int)

Parameters: none pbuff delay_count


Description:Sends out 24 bits contained in the MSDI array to the SPI port.

Pointered version of SendSPI.Function to wait for the desired time.

Module: delay.c delay.c delay.c

Function: GetTick Beeper Count

Syntax: unsigned int GetTick(void) void Beeper(unsigned int) void Count(void)

Parameters: none delay_beep none

Return: ret_val none none

Description:Reads and returns tick as ret_val (tick is incremented on every TIM overflow).

Turns on the Buzzer for the desired time using BeepOn().

Extra display show on the 7 segment display to let things settle at the start.

Module: slider.c slider.c slider.c

Function: Slider WaterSlider MeasureWater

Syntax:void Slider(unsigned int, unsigned int)

unsigned int WaterSlider(unsigned int, unsigned int)

unsigned int MeasureWater(unsigned int)

Parameters: u_val6, u_val7 u_val8, u_val9 u_val_delta

Return: none wdeltaled tmp_measure

Description:

Detects touch via the slider electrodes (E6 and E7), calculates slider value and displays the result on LED Bar.

Detects touch via the water slider electrodes (E8 and E9), calculates and returns the wdeltaled value.

Measures the current level of water and returns that level converted to the water slider range.




Table 5-10. Water Level, Verify Key, Verify Mode Key

Module: slider.c verify.c verify.c

Function: WaterLevel VerifyKey VerifyModeKey

Syntax: unsigned int WaterLevel(void) unsigned char VerifyKey(void) unsigned char VerifyModeKey()


Return:delta_values[4] (5th electrode delta value)

key_number[] (index of pressed key)orNO_KEY_PRESSED

MODE_KEY_PRESSEDorNO_KEY_PRESSED

Description:

Reads and returns the value of electrode E5 (lowest band on the water tube). Used for pumping water out of the tube between modes (from Water pump to Water slider, and from Water Slider to Touch pad mode)

Returns the index of a pressed key if detected, otherwise returns 0.

Returns MODE_KEY_PRESSED if mode key is pressed, otherwise returns 0.



Interrupts

5.5 Interrupts

This application uses a TIM (Timer Interface Module) Overflow Interrupt Figure 5-7. The TOF (TIM Overflow Flag) bit is set when the counter reaches the modulo value programmed in the TIM counter modulo registers.

This interrupt is generated every 160µs. The variable tick, which is used for time delay, is incremented on every TIM Overflow interrupt. Also, the variable beep is tested in this interrupt routine and according to it’s state the Buzzer is turned off or not.

The SCI interrupt service routine is used to provide communication with the PC. It is fully handled by the implemented FreeMASTER sotware.

Figure 5-7. TIM Overflow Interrupt

TIM Overflow Interrupt

clear TOF

tick++

beep ≠ 0 no

return

yes

beep

beep == 0no

Turn off Buzzer

yes



FreeMASTER Software

5.6 FreeMASTER Software

The FreeMASTER software was designed to provide an application debugging, diagnostic and demonstration tool for the development of algorithms and applications. It runs on a PC connected to the controller board via an RS232 serial cable. A small program resident in the MCU communicates with the FreeMASTER software to parse commands, return status information to the PC, and to process control information from the PC. FreeMASTER software, executing on a PC, uses part of Microsoft Internet Explorer as the user interface.

The baud rate of the SCI communication for this application is 57600 baud.

A detailed description of the FreeMASTER software is provided in the dedicated FreeMASTER for Embedded Applications documentation.

The FreeMASTER software Control Page is illustrated in Figure 5-8.

Figure 5-8. FreeMASTER Software Control Page



Chapter 6 Application Setup

6.1 Contents

6.2 Setting Up the Demo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376.3 Power Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386.4 Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386.5 Modes of E-Field Demonstrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386.6 Demo System Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416.7 Starting the Demo System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426.8 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

6.2 Setting Up the Demo

This E-Field Demo consists of two main parts, the Touch Pad Board (TPB) and Water Level Board (WLB) Figure 6-1. The first step is to connect these two PCBs with each other, using connectors J3, J4 on the TPB, and J1, J2 on the WLB.

Figure 6-1. E-Field (Touch Pad Board, Water Level Board)



Power Supply

Figure 6-2. E-Field demo (TPB connected with WLB)

6.3 Power Supply

A DC power connector is provided on the E-Field Touch Pad Board to connect a power supply (a +12V DC switching power supply is provided with the demo). The central terminal of the power connector is positive and should be connected to +12V DC, and the second terminal should be connected to ground.

The +12V DC power supply is connected with a main outlet power cord.

6.4 Communication

On board firmware allows communication with a PC using the FreeMASTER Graphical User Interface. To use it, connect a serial cable from a communication port on your PC to the DB9 (RS232) connector on the Touch Pad Board. The female end of the cable connects to the PC and the male end to the board. The communication speed is 57600 Baud.

6.5 Modes of E-Field Demonstrator

The E-Field demo can work in four modes: Touch Pad, Slider, Water Pump, Water Slider. This application starts in Touch pad mode after it is turned on. The Mode Selection Button is used to switch the demo to the next mode. The current mode is displayed on the Water Level Board LEDs D1 - D4.



Modes of E-Field Demonstrator

Figure 6-3. Mode Selection Button

6.5.1 Touch Pad (Keyboard) Mode

This mode senses the nine electrodes arranged on the Touch Pad Board. They work as a standard keypad. After a touch is detected, the pad number will be shown on the seven segment LED display (DIS1), and on the LED Bar (LEDs D5 - D14) you will see the maximum delta value according to the proximity of the finger.

Figure 6-4. Keyboard



Modes of E-Field Demonstrator

6.5.2 Slider Mode

This mode senses the Slider electrode, which is placed on the Touch Pad Board between the keypad and the mode selection electrode. Moving a finger along the slider, you will see the position of finger on the LED Bar. It is best to move the finger in the center of the slider to correctly activate the electrodes.

Figure 6-5. Slider

6.5.3 Water Pump Mode

In this mode, you pump water from the bottle to the Water Bar on the Water Level Board. To control the water pump, use the two electrodes: Pump Up button and Pump Down button, placed on the keyboard. The level of the water in the column is displayed on the LED Bar and the number of the electrode which is flooded is shown on the display (DIS1).

Touch and hold a finger on the Pump Up (Down) button, and the motor will pump water up (out) to the moment when the Pump Up (Down) button is released. These buttons are active only when you touch them.

If the application is switched to another mode and there is still some amount of water in the Water Bar, the water is pumped out and then, the mode changes.

Figure 6-6. Pump Up (Down) Button



Demo System Setup

6.5.4 Water Slider Mode

Moving the finger along the Water Slider, water will be pumped up or out of the Water Bar. The Water Slider is placed on the Water Level Board near to the Water Bar. Water is pumped to the position of the finger on the Water Slider. Even if you release the Water Slider, water will flow to the last required level.

The level of water in the column is displayed on the LED Bar, and the number of electrode flooded is shown on the display (DIS1).

If the application is switched to another mode and there is still some amount of water in the Water Bar, then the water is pumped out and, after that, the mode will change.

Figure 6-7. Water Slider

NOTE: Using modes where the water is pumped, the bottle should be approximately at the same level as the demo application, otherwise the pump is not able to pump the water.

6.6 Demo System Setup

The following actions and cabling must be completed before the E-Field Demonstrator is started:

• connect the Touch Pad Board (connectors J3, J4) and the Water Level Board (connectors J1, J2)

• fill the plastic bottle with water and put one end of the water pump hose into the bottle

• connect the E-Field demonstrator with a serial cable to the host PC using the DB9 modem connector on the Touch Pad Board

• connect the +12V DC power supply to the power connector on the Touch Pad Board

• turn the demo on by switch SW1 (the application starts with a display show from 0 to F, then starts a calibration of the electrodes)



Starting the Demo System

NOTE: Do not touch electrodes during the calibration. The E-Field demonstrator is ready after the first beep.

This demo has an implemented autocalibration function. Where the buzzer makes a beep with no touching of the demo, it means that the electrodes were calibrated.

The completed demo is shown in Figure 6-2.

6.7 Starting the Demo System

In order to run FreeMASTER on your computer, run the installation file ”fmaster12-38.exe” from the FreeMASTER/freemaster_install directory on the enclosed CD.

Once you have installed the FreeMASTER software, finished the cabling and connected the power supply, turned the demo on with switch SW1, you can start the FreeMASTER program.

6.7.1 Step 1

Start the FreeMASTER program by selecting the Windows menu sequence

Start -> Programs -> FreeMaster 1.2

When the program starts, the screen displays the main application window. If there is no project currently loaded, the window displays a welcome page, as shown in Figure 6-8.

Figure 6-8. Main Window of FreeMASTER Software




The application window consists of three panes: Project Tree, Detail View and Variable Watch.

The Project Tree pane contains a logical tree structure of the application being monitored/controlled. Users can add project sub-blocks, Scope, and Recorder definitions to the project block, in a logical structure, to form a Project Tree. This pane provides a point-and-click selection of defined Project Tree elements.

The Detail View pane dynamically changes its contents depending on an item selected in the Project Tree. You can find detailed information about this pane in the FreeMASTER Software User Manual.

The Variable Watch pane contains a list of variables assigned to the watch. It displays the current variable values and allows you to change them (if enabled in the variable definition).

All the information related to one application is stored in a single project file with the extension ".pmp".

6.7.2 Step 2

Setup the communication for RS232.

If you are running the FreeMASTER software for the first time, you must setup the communication port and communication speed for the PC. The speed of the demo must be set to 57600 bauds.

Open the Options window by selecting the FreeMASTER software menu sequence:

Project -> Options

Select the appropriate COMx port and set up the speed to 57600 baud. See Figure 6-9.

Figure 6-9. Options Window




6.7.3 Step 3

Open the FreeMASTER software project from the enclosed CD.

You can open a project by selecting the FreeMASTER software menu sequence:

File -> Open Project -> E-Field.pmp

See Figure 6-10.

Figure 6-10. Open Project Window

If the project opened successfully, new information will be displayed on the screen. See Figure 5-8. The system works as follows: The FreeMASTER software communicates with the embedded application via a well-defined communication protocol. This protocol allows the PC application to issue commands and to read or modify the embedded application variables. All commands and variables used in the FreeMASTER software project must be specified within the project.



References

6.8 References

1. MC908QB8 data sheet

2. MC33794 data sheet



5. KIT33794DWBEVM - E-Field Imaging Device Evaluation Kit

6. Freescale Reference Manual - Touch Panel System Using the MC33794 E-Field Sensor

7. Freescale AN1985 - Touch Panel Applications Using MC34940/MC33794 E-Field ICs

8. Freescale AN2295 - Developer’s Serial Bootloader for M68HC08 and HCS08 MCUs

9. Freescale AN2395 - PC Master Software Usage

10. Freescale AN2471 - PC Master Software Communication Protocol Specification



Appendix A Electric-Field Contact-less Sensing System Schematics


A1 Freescale Semiconductor

Freescale S

emiconductor

A2

LEVELADC3

SCKMOSICSBPTA3PTB6

LEVEL AMP

+12V

+5V

A1A0

+12V

+5V

J4

HDR 13X2 SHRD.240" HEIGHT.365" OVERALL HEIGHT

J4

HDR 13X2 SHRD.240" HEIGHT.365" OVERALL HEIGHT

1 23 4

657 89 10

11 1213 1415 1617 1819 2021 2223 2425 26

JP2

HEADER 3

JP2

HEADER 3

123

Electric-F

ield C

on

tact-less Sen

sing

System

, Rev. 0

Figure A-1. Schematics “A” of Touch Pad Board

R1OUTT1IN

ADC3

PTB6

PTA3

SCKMOSI

CSBR1OUTT1IN

PTB7

PTB7+5V

+5V

+5V

GNDA

GNDA

GNDA

GNDAGNDA

+12V

PTPT

PTA4PTA5

+12V

LEVEL

OFFSET Adjustment

GAIN Adjustment

+

R910KR910K

J2

CON/CANNON9

J2

CON/CANNON9

594837261

C28 4.7uFC28 4.7uF

C24 100nFC24 100nF

Q1MMBF170Q1MMBF170

C23 100nFC23 100nF

R131MR131M

C2710nFC2710nF

U1

MC68HC908QB8DW

U1

MC68HC908QB8DW

Vdd1

PTB7/TCH32

PTB6/TCH23

PTA5/OSC1/AD3/KBI54

PTA4/OSC2/AD2/KBI45

PTB5/Tx/AD96

PTA3/RST/KBI38PTB4/Rx/AD87

PTA2/IRQ/KBI2/TCLK 9PTB3/SS/AD7 10

PTB2/MISO/AD6 11PTA1/AD1/TCH1/KBI1 12PTA0/AD0/TCH0/KBI0 13

PTB1/MOSI/AD5 14PTB0/SCK/AD4 15

Vss 16

+

-

U4-1

LM358

+

-

U4-1

LM358

3

21

84 D2

BZV55C5V1D2BZV55C5V1

+

-

U4-2

LM358

+

-

U4-2

LM358

5

67

R710KR710K

C20 10nFC20 10nF

R3120R3120

R11100KR11100K

1 3

2

C22 100nFC22 100nF

R52.2KR52.2K

U3

MAX202CSE

U3

MAX202CSE

C1+1

V+2

C1-3

C2+4

Vcc 16

T1OUT 14GND 15

R1In 13

C2-5

V-6

T2OUT7

R2IN8

R1OUT 12

T1IN 11

T2IN 10

R2OUT 9

C25 100nFC25 100nF

R1010KR1010K

R810KR810K

R6680R6680

C26

100nF

C26

100nF

R12100KR12100K

13

2

R42.2KR42.2K

BZ1

Buzzer

BZ1

Buzzer

C211uFC211uF

A3

Freescale S

emiconductor

SHIELDSHIELD

1

E3E3

1

SliderSlider

1 2

E4E4

1

E1E1

1

E8E8

1

J3HDR 13X2 SHRD.240" HEIGHT.365" OVERALL HEIGHT


1 23 4

657 89 10

11 1213 1415 1617 1819 2021 2223 2425 26

E9E9

1

REF_AREF_A

1

E6E6

1

E7E7

1

E5E5

1

E2E2

1

Electric-F

ield C

on

tact-less Sen

sing

System

, Rev. 0

Figure A-2. Schematic “B“ of Touch Pad Board

+5V

+5V

GNDA

GNDAGND

+12V

PTA0PTA1PTA4PTA5

+12V +5V

LEVEL

OFF

ON

U2

MC33794DWB

U2

MC33794DWB

RST1WD_IN2

NC13

NC25

LAMP_GND4

LAMP_OUT6

NC37

LAMP_SENSE8LAMP_MON9

DIS_SHIELD10

D11C12B13A14

SIGNAL15

LEVEL16

PWR_MON17

LP_CAP18

R_OSC19

NC420 NC5 21NC6 22NC7 23

CLK 24

VDD_MON 25VDD 26VPWR27

VCC 28

AGND29

SHIELD 30

NC8 31

GND32

NC9 33NC10 34

TEST35

E1 36

E2 37

E3 38

E4 39

E5 40

E6 41

E7 42

E8 43

E9 44

REF_A 45

REF_B 46

ISO_OUT 47

NC11 48NC12 49NC13 50

ISO_IN 51

NC14 52

ISO-9141 53LAMP_CTRL54

R147KR147K

R239KR239K

C71nFC71nF

C410nFC410nF

JP1

HEADER 3

JP1

HEADER 3

123

C17 10nFC17 10nF

C18 10nFC18 10nF

C210nFC210nF

GC1GROUND CONNECTION

GC1GROUND CONNECTION

C110uFC110uF

C64.7uFC64.7uF

C15 10nFC15 10nF

C14 10nFC14 10nF

C13 10nFC13 10nF

C12 10nFC12 10nF

SW1SwitchSW1

Switch

21

3

D11N4148D11N4148

C11 10nFC11 10nF

C19 56pFC19 56pF

C310nFC310nF

C10 10nFC10 10nFC8

10nFC8

10nF

J1+12V External power supplyJ1+12V External power supply

+V 1

-V1

2

-V23

C9 10nFC9 10nF

C54.7uFC54.7uF

C16 10nFC16 10nF

Freescale S

emiconductor

A4

SCKMOSICSBPTA3PTB6

+12V

+5V

Power ON



1 23 4

657 89 10

11 1213 1415 1617 1819 2021 2223 2425 26

R1560R1560

.

DIS1

HD-A103

.

DIS1

HD-A103

CA 3CA 8

DP 5G10F9E1D2C4B6A7nFnF

Electric-F

ield C

on

tact-less Sen

sing

System

, Rev. 0

Figure A-3. Schematic of Water Level Board

MOSISCKCSB

PTA3PTB6

D1D2D3D4D14D13D12

D5D6D7D8D9D10D11

D1

D2

D3

D4

D5

D6

D7

D8

D9

D10

D11

D12

D13

D14

+12V

+5V

+12V

+5V

+12V

+ C447uF

+ C447uF

C510uFC510uF

D3

RED

D3

RED

D7

RED

D7

RED

U1

MC33993DWB

U1

MC33993DWB

GND1

SI2

SCLK3

CS4

SP05

SP16

SP27

SP38

SG09

SG110

SG211

SG312

SG413

SG514

SG615

VPWR16 WAKE 17SG13 18SG12 19SG11 20SG10 21SG9 22SG8 23SG7 24SP4 25SP5 26SP6 27SP7 28INT 29

AMUX 30VDD 31

SO 32

SliderSlider

12

D5

RED

D5

RED

E3E3

1

C333nFC333nF

D4

RED

D4

RED

E5E5

1

SHIELDSHIELD

1

D9

RED

D9

RED



1 23 4

657 89 10

11 1213 1415 1617 1819 2021 2223 2425 26

C110C110

U2

MC33886DH

U2

MC33886DH

PGND 9

PGND 10

PGND 11

PGND 12

AGND 1

OUT1 6

OUT1 7

OUT2 14

OUT2 15

V+ 4

V+ 5

V+ 16

FS2

IN13

IN219

DNC8

DNC20

D118

D213

CCP17

D2

RED

D2

RED

E2E2

1

C210nFC210nF

D8

RED

D8

RED

J3

CON/2screws

J3

CON/2screws

12

D12

RED

D12

RED

D10

RED

D10

RED

D6

RED

D6

RED

D11

RED

D11

RED

D13

RED

D13

RED

E4E4

1

E1E1

1

D1

RED

D1

RED

D14

RED

D14

RED

Appendix B Electric-Field Contact-less Sensing System Bill of Material

Touch Pad Board BOM

Reference Part Value Description Mfg. Mfg. Part No.

BZ1 3-16 V/ 6mA Buzzer any acceptable

C19 56 pF/ 50 VSMD Ceramic

Capacitor, 0805any acceptable

C7 1 nF/ 50 VSMD Ceramic

Capacitor, 0805TDK C2012X7R1H102K

C2, C3, C4, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C20, C27

10 nF/ 50 VSMD Ceramic

Capacitor, 0805 TDK C2012X7R1H103K

C22, C23, C24, C25, C26

100 nF/ 25 VSMD Ceramic


C21 1 uF/ 16 VSMD Ceramic

Capacitor, 0805TDK C2012X7R1C105K

C5, C6, C28 2.2 uF/ 16 VSMD Ceramic

Capacitor, 0805TDK C2012X7R1C225K

C1 10 uF/ 16 V SMD Ceramic

Capacitor, 1210 TDK C3225X5R1C106M

D1 1N4148SMD Switching Diode,SOD-80C (minimelf)

any acceptable

D2 BZV55C5V15.1 V Zener Diode,

SOD-80C (minimelf)PHILIPS BZV55-C5V1

J1 PWR JackPower Jack type connector 2.1mm

Elekon K375A

J2 DB9/ female, 90°Connector (RS232/

9pin)

J3, J4Boardmount

SocketPCB socket 2x13 way 3M 8526-4500PL

JP1, JP2 1x3 Pin Header

Q1 MMBF170SMD MOSFET

N-channel transistor, SOT23

ONSEMI MMBF170LT1

R1 47K SMD Resistor, 0805 any acceptable

R2 39K SMD Resistor, 0805 any acceptable

R3 120 SMD Resistor, 0805 any acceptable

R4, R5 2.2K SMD Resistor, 0805 any acceptable


R7, R8, R9, R10 10K SMD Resistor, 0805 any acceptable

R13 1M SMD Resistor, 0805 any acceptable


B1 Freescale Semiconductor

R11, R12 100KMulti turn cermet

trimmer (64Y)VISHAY/ Spectrol

594-64Y104

SW1 Switch Slide SPDT Top button APEM 25136NAH

U1MC68HC908QB

8DW8 bit Microcontroller FREESCALE MC908QB8CDWE

U2 MC33794 E-Field sensor chip FREESCALE MC33794DWB

U3 MAX202 RS232 chip Maxim-Dallas MAX202CSE

U4 LM358IC Dual OpAmp (surface mount)

ONSEMI LM358D

Water Level Board BOM


C1, C2 10 nF/ 50 VSMD Ceramic


C3 33nF/ 50VSMD Ceramic

Capacitor, 0805any acceptable

C4 47uF/ 16VSurface Mount

Electrolytic capacitorany acceptable

C5 10 uF/ 16 VSMD Ceramic

Capacitor, 1210 TDK C3225X5R1C106M

D1 - D14 LED diodeRed SMD LED diode,

0805KINGBRIGHT KP-2012SURC

DIS1 LED displaySingle digit numeric

display (common anode)

KINGBRIGHT SA52-11EWA

J1, J22x13 way Header

Male PCB Mounting Header, 90°

EZK MLW26A

J3 CON/ 2screws 2 pin connector EZK CZM5/ 2


U1 MC33993 MSDI Device FREESCALE MC33993DWB

U2 MC33886 H - Bridge FREESCALE MC33886DH

front windshield filling unit - APO 040.01, 12V DC, manufacturer: SEV

Touch Pad Board BOM



Freescale Semiconductor B2

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APPEFIELDRM Rev. 009/2006

Documents

Electric-Field Contact-less Sensing Systemcache.freescale.com/files/sensors/doc/ref_manual/APPEFIELDRM.pdf · 2.3 Principle of Operation ... The Electric-Field Contact-less Sensing