PH4705 & ET4305: Digital Sensors

Simple switches to data words– Switch: micro-switch, reed relay, Hall sensor,

optical switch…..– Threshold or Set point detector– Counting, timing, finding the frequency– Sensors that generate data words directly– Complex IC sensors that generate serial data

or connect to a bus system

PH4705 & ET4305: Digital Sensors

Switch

Input ON/OFF information

mechanical movement

micro-switch,

reed relay operated by a magnet

Hall effect sensor

PH4705 & ET4305: Digital Sensors

PH4705 & ET4305: Digital Sensors

Switch

Light Beams

LDR-light dependant resistor

Photo-diode

Photo-transistor

Slotted and reflective sensors

PH4705 & ET4305: Digital Sensors

PH4705 & ET4305: Digital Sensors

Logic Signal input

ON/OFF input

Compatible logic signal (voltage levels, available current)?

Interference and noise?

PH4705 & ET4305: Digital Sensors

Threshold or Set Point Detection

Analogue input signal, detect when its value passes through a set point or threshold (in either direction)

PH4705 & ET4305: Digital Sensors

Threshold detector with hysteresis

Zero crossing detectorInput

Output

Potential Divider Sets Threshold

Threshold or Set Point detector

PH4705 & ET4305: Digital Sensors

Counting, timing, finding frequency

The required data derived from switch sensors may be:

number of pulses

time between pulses

width of pulse

frequency of pulses ………..

PH4705 & ET4305: Digital Sensors

Data WordsTypical example is this optical coded disc used to detect angular position. Looking along a radius gives an 8-bit word or a resolution of 1/256.

(Looking at the pulse rate of, say, the outside markings will also yield speed.)

PH4705 & ET4305: Digital Sensors

Complex IC digital sensor

Sensors system ICs that have signal processing and generate digital data as a serial data streams or connect directly to a microprocessor system data bus.

Examples: CCD digital camera sensor,

SHT75 temperature/humidity module

PH4705 & ET4305: Digital Sensors