View Full Version : Infrared detector in place of a phototransistor ??

11-05-2009, 10:27 AM
Can I use the infrared detector that comes with the Boebot, coupled with an infrared LED, in place of a phototransistor & light source, for detection of an object breaking the beam?· The application is in a "jam detector", as in a photocopier, that would have 3 horizontally spaced stations with a gap (vertically) between the IR LED and IR detector.· If 2 adjacent detectors sense paper (the beam is blocked), this signifies a jam - if not, all is well.· I know the IR LEDs & detectors are used with the Boebot in a reflective mode.· Can I use them with the LED pointed toward the detector, and when the beam is broken, the detector output changes state?· Thank you for any light (IR or otherwise) you can shed on this.



PJ Allen
11-05-2009, 10:38 AM

11-05-2009, 10:40 AM
Two problems I see, not all paper is opaque to IR and the detector sold by Parallax responds to 38khz pulsed IR so you would need a driver. Why not get a replacement phototransistor?

- Stephen

11-06-2009, 12:37 AM
The detector sold by Parallax outputs for a little while after the pulse has gone away. This is how you can use an IR-LED (using FREQOUT IR_Pin, 1, 38000) to illuminate the detector, then IMMEDIATELY do a "PULSIN DetPin, ResVal" to get a "ResVal" pulse width.

So yes, you can do this, assuming the paper isn't transparent to IR light -- which I'd be amazed if it was.

11-06-2009, 02:41 AM
Thank you gentlemen !! I think I'll get some phototransistors to do the job, in line with using the KISS method.