I recentently purchased the lynxmotion IRPD and i’m having a problem.
I connected it to the basic stamp BOE.
The IR Sensor Output is high when no IR-LED is on. That is correct.
But when one of the IR-LEDs is on, the Sensor output is ALWAYS low, even if I put black tape, of ieces of cardboard around the LEDS, and around the Sensor.
When no light from the LED’s can enter the sensor, how can the output voltage be low?
I already tried a 100 uF capacitor between +5V and ground. Doesn’t help.
It would help to see the wiring, and code you are trying to use.
Also here is the online support info for the IRPD.
Note: We have found at least one IRPD that was not working because the oscillator was dead. It was an easy fix, just pan the frequency pot, and return it to the original position. Probably due to a cleaner used in the manufacturing process creating a film on the resistive element. If available put an oscilloscope across one of the IR LED’s, enable that channel, and adjust the freqency pot for 38khz.
Note: The most common problem with the IRPD is when people miss where it says in the manual; “Caution! The Panasonic IR Detector can sense the light directly from the LED’s. This can cause the IRPD to report false readings. To prevent this, put a small piece of black electrical tape on the back and sides of the IR Detector.”
Note: The LED enable inputs are CMOS and will float high if not connected to anything. Make sure the inputs are tied to ground or +5vdc when testing.
Note: The IRPD is most commonly used by checking for obstacles constantly and adjusting the vehicle direction in small increments. Over time the robot will gently steer away from obstacles. This means the sensor is less sensitive than when used in other ways. Sometimes it will be necessary to detune the oscillator to make it less sensitive. The IRPD is polled from a microcontroller. This is normally done after enabling either the left OR right LED for about 1mS. This will usually result in proper operation from the unit. However if you want to leave the LED enable on for longer, then you need to detune the oscillator. I would recommend you follow these instructions.
Adjust the LED drive to it’s maximum.
Adjust the oscillator to full counter clockwise.
Constantly poll, or turn on ONE of the two LED enables.
Adjust the oscillator slowly until the red LED starts to flicker, then turn it back till it just goes off steady.
Pass your hand in front of the unit and you should see the red LED light up solid.
Adjust the LED drive to reduce the range till you are happy with the performance.
Testing with a Microcontroller
The best way to accurately test the IRPD is to connect it to a microcontroller and write a control program. I have included general purpose Basic programs for the First Step and the Next Step microcontrollers. Follow this procedure to test and verify it’s operation. If you have trouble, it will most likely be getting the detector to not “see” the floor. You may need to experiment with the alignment and positioning of the LEDs.
Apply power to the IRPD from the First Step or Next Step I/O bus.
Adjust the LED drive to the mid position between minimum and maximum.
Enter the correct program on page 6 in the users manual into the Stamp editor and program the Stamp with it.
Position the IRPD so it is pointing away from any objects. The LEDs should be off.
Place your hand directly in front of the PC board about 4" away from the sensor. The status LEDs should be on steady. If not quickly remove power and double check your wiring!
Move your hand about 4" from center to the left. You should see the left LED on only.
Move your hand about 4" from center to the right. You should see the right LED on only.
Move your hand from side to side to see the field of vision.
Now move your hand slowly away from the detector and take note when the LEDs just start to flicker. This is how far the sensor can “see” an obstacle. If it is too far, adjust the LED drive pot to the right for less current to the IR LED, and less distance. If it is too close, adjust the LED drive pot to the left for more current to the LEDs and more distance.
Testing without a Microcontroller
You can test the IRPD without a microcontroller by following these instructions.
Apply +5vdc and ground to the red and black wires.
Apply +5vdc to the left LED enable (blue) wire.
Adjust the LED drive to the minimum, full clockwise.
Mount the IRPD so it is pointing away from any objects. The LEDs should be off.
Move your hand about 4" from center to the left. You should see the left LED on only. The Left Status LED should be on. If not quickly remove power and double check your wiring!
Now move your hand slowly away from the detector and take note when the LED just starts to flicker. This is how far the sensor can “see” an obstacle. If it is too far, adjust the LED drive pot to the right for less current to the IR LED, and less distance. If it is too close, adjust the LED drive pot to the left for more current to the LEDs and more distance.
Remove the +5vdc to the left LED enable (blue) wire and apply +5vdc to the right LED enable (violet) wire. Repeat the process for the right side.
Other notes
You can ensure the LEDs are illuminating by using a IR detector, or a camcorder in a dark room. The LEDs will show as a dim light. When writing programs for the IRPD you must cycle the LED’s. Do this as follows:
LED ON
pause 1mS
LED OFF
pause 1mS
LED ON
pause 1mS
check sensor
LED OFF
pause 1mS
Then repeat for the LED on the other side.
The cycle times of 1ms were used because it is a standard used in the “pause” command of microcontrollers. The actual device responds better to a 600uS cycle time. If you find an item not covered in this list, please let me know, and I will add it. Thanks, Jim
