remote control IR receiver with photodiode

David B

Has anyone done any IR remote control receiving with just a raw IR receiver photodiode?

I have an IR receiver from a Radio Shack component set "Matched Infrared Emitter and Phototransistor Detector Model 276-142".

Last night I set up the detector on a breadboard in a simple circuit with the receiver diode feeding the base of a transistor and a scope showing the transistor response. After a little tweaking, it showed a good response from several surplus remote controls.

There are lots of objects in the OBEX for decoding the IR remote control signal but it looks like all of them are written to use a dedicated IR remote receiver module with a built-in filter for the 38 or so kHz rate pulses. The objects warn that some remotes will not be detected with that unit if their modulated frequency is too far off from the 38 kHz of the receiver, so it seems that there could be some benefit from using a raw photodiode receiver which should receive everything.

Has anyone written code (preferably propeller) to decode IR signals from the raw pulses?

erco

The 38 (and older 40 kHz) IR modules have lots of internal hardware, including filters & integrators that do a pretty fine job of reliably reading an IR remote signal in noisy environments that would saturate and shut down a plain phototransistor. Discrete phototransistors certainly have their applications, but these 38 kHz modules are so cheap and reliable that most people start off with them first. That's probably why you don't see many phototransistor objects in the exchange.

David B

Ok, that makes sense.

For my tests, I was pointing the remotes at the diode from about 3 inches, so a low gain amplifier worked well with no noise and interference problems.

At one point I had tweaked a little higher gain in the circuit, and 60 hz line noise and ambient light level shifting started creeping into the signal.

So for distances like 5 or 10 feet or more, I could see getting one of those detectors, but to try this detector out for use as a general purpose propeller development board data input port probably at just a few inches, I guess I'll go on and use this diode. Besides, it should be an interesting project to get working.

erco

Re: the center frequency and response of the IR modules, I bought some 56K modules: http://www.pololu.com/catalog/product/837

I wanted to use a 56 khz system simultaneously with 38 khz, hoping they would not interfere. To my chagrin, the 56 khz units pick up a signal from a standard 38 kHz TV remote just fine at close proximity. Remotes work so well because they absolutely BLAST such an overwhelmingly strong pulsed signal. An EE friend who specializes in IR says some pulse a full AMP of current through their poor little IR LED for short periods.

One more good reason why most remotes stop sending if you hold a button down (or sit on the remote!) for over 10-20 seconds: to let the LED cool down!

David B

It's funny; I was digging through my parts box looking for another transistor to add more gain to the IR detector when what did I find but a Parallax Panasonic PNA4602M 38 kHz IR receiver module! I must have bought it a few years ago and forgot about it.

I wired it on a breadboard, hooked it up to my scope and it worked great (except for the odd glitch that I couldn't find the simple pinout configuration of the module anywhere in the Parallax documentation; I had to search the internet for it.)

So now my plan is as long as I've got both detectors, why not make a module with both detectors to plug into my propeller breadboard. I must have a dozen or more old remotes to experiment with, and this'll make a great IR test bed.

PJAllen

You can heatsink LEDs (IREDs), too, by soldering the big part of them, the die, to an area of copper on your board (not to a trace.) If you have access to copper tape, use that.