Infrared LED / detector design
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From: Matt on 19 Feb 2010 11:03 Hello. It's been a while since I've posted. I'm working on an Ir LED / detector for a small robot platform I've made. I'm just having fun really, and learning! I've read a considerable amount about this and I'm not getting concrete facts (or at least what I want to hear) I purchased a Ir emitter and detector matched pair from Radio Shack Model: 276-142. I've not found a real datasheet for these, which seems to be a common problem. What I do know from bench testing is the detector triggers from the emitter pulses all the way from DC to 30kHz and probably higher frequency than that. I just tested to 30kHz. I drove the emitter at 1.3V, 86mA 50% duty cycle squarewave pulse. The detected distance was about 6" I also drove the emitter at 1.3V 100mA, the detected distance was about 36" From my reading, modulating the emitter at some frequency is useful for eliminating false triggers from ambient Ir sources. I understand that. What I need help on is tuning the detector to that frequency. How is this done??? The detector is a phototransistor. Having no datasheet isn't helping any. Currently the detector is seeing the emitter and pulses just fine, but it also sees any other sources as well (halogen recessed lighting in particular!). Thank you
From: Jan Panteltje on 19 Feb 2010 11:27 On a sunny day (Fri, 19 Feb 2010 08:03:18 -0800 (PST)) it happened Matt <hamplifier(a)gmail.com> wrote in <9184f2dc-de55-4a2b-b50c-b68768a204aa(a)a18g2000yqc.googlegroups.com>: >Hello. It's been a while since I've posted. I'm working on an Ir LED / >detector for a small robot platform I've made. I'm just having fun >really, and learning! > > >I've read a considerable amount about this and I'm not getting >concrete facts (or at least what I want to hear) > >I purchased a Ir emitter and detector matched pair from Radio Shack >Model: 276-142. I've not found a real datasheet for these, which seems >to be a common problem. > >What I do know from bench testing is the detector triggers from the >emitter pulses all the way from DC to 30kHz and probably higher >frequency than that. I just tested to 30kHz. > >I drove the emitter at 1.3V, 86mA 50% duty cycle squarewave pulse. The >detected distance was about 6" >I also drove the emitter at 1.3V 100mA, the detected distance was >about 36" > >From my reading, modulating the emitter at some frequency is useful >for eliminating false triggers from ambient Ir sources. I understand >that. > >What I need help on is tuning the detector to that frequency. How is >this done??? The detector is a phototransistor. Having no datasheet >isn't helping any. Currently the detector is seeing the emitter and >pulses just fine, but it also sees any other sources as well (halogen >recessed lighting in particular!). > >Thank you Moduklate a carrier. For example FM. That gives you 2 (two) advantages, the 2 are: 1) You can detect for presence / non precense of the carrier (signal good). 2) Your system does not respond to other signals so much. 3) You can use a bandpass filter in the receiver. 4) Use a packet system, that allows you to comunicate with more then one robot device. 5) Forget about IR and go to 430 MHz radio modules, because IR sucks. I have tried both.
From: Matt on 19 Feb 2010 12:19 Yea? Thank you, I should have mentioned it's not for data transmission. Sorry about that. My idea is an array or Ir units (maybe 3 or 4) around the bot to be used for navigation.
From: Jan Panteltje on 19 Feb 2010 12:45 On a sunny day (Fri, 19 Feb 2010 09:19:20 -0800 (PST)) it happened Matt <hamplifier(a)gmail.com> wrote in <4db548d2-408e-4468-b0b6-b5aec7d1f892(a)g28g2000yqh.googlegroups.com>: >Yea? Thank you, I should have mentioned it's not for data >transmission. Sorry about that. > > >My idea is an array or Ir units (maybe 3 or 4) around the bot to be >used for navigation. Well I do no see how that should work, how does it work? But you can modulate the LEDs with for example a 74HC4046 chip. use the VCO in the transmitter for frequency shift for example. And you can use same chip in the receiver as PLL for either analog demodulation (in case you wanted to transfer sound for example), or digital demodulation. By assigning different frequencies for each transmitter you could perhaps create some sense of direction in the robot. Or use GPS :-)
From: Matt on 19 Feb 2010 12:57
The idea is pretty simple...... I think..... :) The robot runs around in the house...... If is gets close to the left wall (like in a hallway) the left Ir emitter/detector sees the reflection and the robot veers slightly right. At the moment I'd like to only run two tx/rx pairs for left and right to get me down a hallway and make some simple decisions to move about. There are a lot of holes in this theory, but the Ir parts are cheap, and I'm having a little fun in the process. Supposedly I can tune the detector by adjusting RL, but that's off a datasheet from another part. Radio Shack sucks. No datasheet, How can they justify this!? |