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Electronics => Electronics => Topic started by: Bobble on April 01, 2008, 06:57:46 AM

Title: Help with debugging a Basic IR emitter/detector circuit that refuses to detect
Post by: Bobble on April 01, 2008, 06:57:46 AM

Hi there,

Being the budding Mechatronics engineer that I am, I've made up a few basic IR detector/emitter circuits for a project. This is all well and good, and as it is a simple circuit, two resistors (as per the basic IR schematic on the tutorial. For reference though r1=270, r2=10k). As for the emitting and receiving diodes, they're being used inside their operational limits (for reference the emitter is a op298b and the recovering a z1956). I'm running a regulated 5 volt current into the circuit, and theres no shorts and it looks just like the schematic.

So in theory, it should work no? So I as I lacked the IC with me, I tested it with a multimeter. As the Vout essential gives the voltage at that point i figured I could just measure the Vout using a voltmeter and I got a voltage (so far so good). I removed my foil+tape shielding from my emitter, and to my dissapointment the Vout (which i was measuring as the voltage across the receiver's pins) remained constant. No matter what I did, changing the orientation of the emitter and receiver and using shielding or reflective surfaces to cover or uncover the diodes, all voltages of the circuit remained static.

I figured maybe it' wasn't sensitive enough, so I halved and then further reduced the resistor values. Whilst this did change the voltage readings, they remained static at this changed level. After this I redid my circuit, using different components (the same types though), and yet I get the exact same values and static nature. I checked with a camera to see if my emitter is in fact, emitting, but the little purple light was visible. So it all points to the detector.

This makes no sense to me, given what (little) I know about diodes and electronics. If I change the conditions that the emitter and detector are operating in shouldn't this then lead to some sort of change in voltage readings, no matter how small? Isn't that what the Vout to the IC measures? If nothing else, static levels can't be good.

I've tried most of the possibilities I can think of, short of buying different types of components (perhaps it being a compatability issue, though I will attempt this shortly). Sadly the internet and tutorials present on the subject I've followed and yet it it seems no one even could think that this simple setup might not work. I just know though it has to be something simple I'm overlooking, and yes it is turned on. Perhaps the components are playing an April fool's joke on me.

Title: Re: Help with debugging a Basic IR emitter/detector circuit that refuses to detect
Post by: Admin on April 06, 2008, 01:14:04 PM

Hmmmm can you show us the circuit you are using and tell us the exact resistor values you are using on the detector circuit?

Did you select your resistors based on this tutorial?
http://www.societyofrobots.com/schematics_photoresistor.shtml