Using Multiple MaxSonar Sensors · 2015. 1. 2. · Figure 2 Figure 3 Control the MaxSonar Sensors to Range Simultaneously (works for most instances) Connect all the MaxSonar® RX

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Using Multiple MaxSonar® Sensors| Written By: Tom Bonar | DatePosted: 07112012 |

When using a single sensor, typically it is possible to just let it rangecontinuously in free run mode. This method is easy and works well.

Please consult your sensor datasheet or Finding Distance UsingAnalog Voltage for calculation formulas for analog voltage todistance.

This guide covers:‑Free Run Operation‑Simultaneous Operation‑Commanded Sequential Reading‑Constant Looping Operation

Please consult your sensor datasheet or Finding Distance UsingAnalog Voltage for calculation formulas for analog voltage todistance.

Free run all Sensors(not recommended)

Continuous free run operation will generally not work when using more than one sensor in the samesystem. If you leave Pin 4 (the RX pin) unconnected so that the sensors range continuously, at startupthe sensors will range at exactly the same time. Since the sensors are not synchronized, the sensorswill range with slightly different intervals. Slowly the sensors will stop ranging at the same time. Thesefrequency drifts will likely cause interference between sensors for most applications. If looking at theanalog voltage output from the MaxSonar®, this will appear as voltage noise that occurs at someregularly occurring rates. Additionally, the digital outputs will have phantom readings at some regularlyoccurring rates.

This is because the sensor "noise" is actually interference from other sensors, not actual noise. Thesensors are just behaving the way they were designed to behave. This describes the general resultsthat you would be getting (as verified by a voltmeter). This issue becomes more apparent at longerdistances, to the point that the sensor readings are very rarely reliable.

The reason the action is happening is because the sensors are not operating synchronously with eachother or at the same speed. One sensor may be operating slightly faster than the other. For example;sensor 1 is operating at 49.0mS while sensor 2 operates at 49.2mS. When the sensors are notsynchronized, one sensor may be in transmitting mode while the other sensor is in receiving mode.Because this action is happening, the sensor is receiving the pulses from the sender and not its ownpulse bounce back. The closer the sensors are in synchronization, the longer the stable period is. Thefarther out of synchronization the sensors are, eventually they may not even appear to functionproperly. This happens because the stable period is extremely short or there is no period of stability.

Figure 1 below shows a single sensor operating, detecting an object at 96 inches with now other sensorspresent. Figures 2 and 3 show the operating of a sensor if other sensors are operating in the area infreerun operation. As the sensors become more unsyncronized the range readings become more andmore unstable.

Figure 1. Single Sensor operation

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Figure 2

Figure 3

Control the MaxSonar Sensors to Range Simultaneously(works for most instances)

Connect all the MaxSonar® RX lines together, and connect to your control circuit such as a pin on amicrocontroller (or even a 555 timer set up to strobe high for at least 20uS with a period betweenstrobes great or equal to timing that has been stated in the sensor datasheet).

To view a wiring diagram of what this set up should look like view figure 4.

Figure 4

For the MaxSonar sensors you can start all the sensors at the same time by pulling the RX pins high forthe 20uS. For the LVMaxSonar sensors this can be done as often as every 50ms. For the XLMaxSonarsensors this can be done as often as every 100mS or more. This will sync the MaxSonar® sensors totake readings at the same time.

The MaxSonar® sensors, because of continuously variable gain, will typically ignore adjacent sensorswhen running simultaneously. This method is especially convenient when using the analog voltage (ANoutput), as the analog voltage can be read at any time.

This method works for all sensors lines. We used an LVMaxSonarEZ line to show the diagram. As longas Pin 4 (RX) is connected to the same trigger device all the sensors will range simultaneously.

Sequentially Read Each MaxSonar®(Always Works)

To sequentially read each sensor, connect your triggering device to pin 4 (RX) of the first sensor, thenconnect pin 5 (TX) output of the first sensor to the RX pin of the next sensor that is to be ranged insequence. Do this with however many sensors are to be used in the chain. To view a diagram of howeach chaining diagram is wired view figures 5 through 8 below.

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http://www.maxbotix.com/articles/041.htmhttp://www.maxbotix.com/pictures/articles/031-Simultaneous.jpghttp://www.maxbotix.com/articles/041.htm

Figure 5 LVMaxSonarEZ and XLMaxSonarEZ/AE Diagram

Figure 6 HRLVMaxSonarEZ diagram

Figure 7 MaxSonarWR and MaxSonarWRC diagram

Figure 8 HRXLMaxSonarWR and HRXLMaxSonarWRC diagram

To start the commanded sequential reading for the MaxSonar sensors, trigger the first sensor to range.This allows each device to range only after the previous has finished (every 50mS for the LVMaxSonarsensors or every 100mS for the XLMaxSonar sensors). This method will always work. There will not beany interference between sensors, but ranging frequency drops by the factor of the number of sensorsused.

Continuous LoopingTo have the circuit continuously loop so the chain is always giving an analog voltage output, connect pin 5of the last sensor in the sequence to pin 4 of the first sensor in sequence with a 1K resistor in sequencebetween the pin 5 output and pin 4 input. For a diagram of how the wiring should look for the MaxSonarsensors operating in a Continous Loop please see figures 9 through 12 below.

http://www.maxbotix.com/pictures/articles/031-Command-Looping-Chaining-HRLV.jpghttp://www.maxbotix.com/pictures/articles/031-Command-Looping-Chaining.jpghttp://www.maxbotix.com/pictures/articles/031-Command-Looping-Chaining-HRXLWR-WRC.jpghttp://www.maxbotix.com/pictures/articles/031-Command-Looping-Chaining-WR-WRC.jpg

Figure 9LVMaxSonarEZ and XLMaxSonarEZ/AE Constant Chaining Loop Diagram

Figure 10HRLVMaxSonarEZ Constant Chaining Loop Diagram

Figure 11XLMaxSonarWR and XLMaxSonarWRC Constant Chaining Loop Diagram

Figure 12HRXLMaxSonarWR and HRXLMaxSonarWRC Constant Chaining Loop Diagram

With these sensor chaining methods, once pin 4 is pulled high for 20uS on the first sensor, all sensors willchain sequencially. After the micro controller brings pin 4 high, the micro controller will have to return it’spin to a high impedance state so that after the sequence is complete the TX signal output from the lastsensor will trigger the RX of the first sensor.

http://www.maxbotix.com/pictures/articles/031-Constant-Looping-Chaining-WR.jpghttp://www.maxbotix.com/pictures/articles/031-Constant-Looping-Chaining-HRLV.jpghttp://www.maxbotix.com/pictures/articles/031-Constant-Looping-Chaining.jpghttp://www.maxbotix.com/pictures/articles/031-Constant-Looping-Chaining-HRXLWR.jpg

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