IR sensor as proximity sensor

I am trying to use an IR receiver module from radio shack (PN 276-640) along with an IR LED (276-0143) to detect objects as close as 2 inches, but I am not getting any response from the receiver. I posted my circuit, and made it public, but I don't know how to embed it in this note. I called it "IR Sensor".

I think I have the circuit set up correctly, but when I watch the Vout of the Receiver, the voltage never changes. I expect there to be some kind of change that I can use to calibrate to represent an object at distance x.

All my google searches keep bringing me to the Society of Robots Web site but that is no help to me.

by Graubot
December 15, 2012


So, it works like this:

Link & Share > URL > copy and paste URL:


Link & Share > CircuitLab > copy and paste CL link:

Then read:

by signality
December 16, 2012

Step one, figure out how to post here...

Sweet, that was easy, now that I know, thanks!

by Graubot
December 16, 2012

You don't want an IR demodulator, which that receiver module is. Try a simple photodiode (pick one with IR response).

To use the demodulator, you'd need to send a modulated signal through the IR LED. The whole purpose of the demodulator is to separate a modulated signal from background light... and your LED output is being considered background light and removed, since it's not the right frequency.

by bvoigt
December 17, 2012

Thanks, your right!

I need to operate at 38KHz, so I changed the circuit to include a 555 timer to generate that rate. For some reason, when I tried to run the IR LED from the output of the timer, I couldn't get the right frequency, but then I switched the LED to the discharge pin (as shown) and now it works.

However, I still am working on the response from the receiver. I will draw up another circuit showing that side, but I still do not get any change in out put over there. But when I point my TV remote at it and push something, the response drops about .5V (although this is not stable, it seems to jump around by about .3V).

I tried using the IR detector from the RS 276-0142 kit, but again, no responses at all. I will try to rebuild that circuit again because I am only trying to determine proximity to an object at about 3 inches, and it seems overkill to use the timer and additional parts. Any help here would be greatly appreciated.

by Graubot
December 19, 2012

So here is my Receiver Module, but I do not know how to actually include this module in the drawing. I picked a component that looked like it (only without the light control aspect).

So the module specifies that it works at 2.4 - 5.5 V supply, with a supply current of 0.6mA under no signal, center frequency of 38 KHz, passband of 940 nM +- 50, and at a range of up to 42.6 feet.

Of course, radio shack part, so no datasheet, however, I found one for a Sharp part that seems to be very similar (GP1UM261XKVF).

I am trying to sense the proximity of an object at about 3 inches, and I thought that I could calibrate the output voltage of this device when used in conjunction with my previous posted IR LED circuit (and yes, I have both circuits running from the same battery source).

However, no response from the receiver when I use the LED circuit. I measured the frequency and it is right on the 38 KHz mark. But, when I point my TV remote at the receiver and push a button, I do see a small drop in voltage, with some jumping around (0.5V drop and .3v jumping around). As I stated earlier, I don't actually need anything this complicated, however, it does seem to offer some protection from other light noise that the alternative IR detector would be open to. Or so I think????

Suggestions anyone?

by Graubot
December 19, 2012

If you bounce your TV remote off an object (indirect signal path), do you still get a response? If yes, look for problems in your LED circuit. If not, you may have a sensitivity problem with the receiver.

by bvoigt
December 19, 2012

i) Be aware that if you update a schematic that you have used as a reference in a post: that reference updates so the post may then refer to things that are no longer visible. It's a good plan to leave circuits that you have pasted into posts unchanged and save changes as new circuits.

ii) The CL 555 timer model is broken:

iii) It really doesn't help buying uncontrolled stuff with no proper datasheet ...

These are the 276-0142 IR LED + photodetector pair from Radio Shack:

The Sharp GP1UM261XKVF is a totally different device:

Get yourself an account with Farnell.

iv) This section of the link I posted earlier:

basically shows you how to model a simple LED + photodetector pair with no background light blocking i.e. the receiver is direct coupled and so has no AC coupling capacitor to decouple the essentially DC background light.

If you make the photodetector in this:

into the sort of photodetector circuit shown here

and ac couple V(out) into a transimpedance (TIA) such as shown in:

but bias the non-inverting i/p of the opamp to somewhere around mid supply then you get this:

which is along the right lines.

by signality
December 19, 2012

Thanks. I noticed that my previous postings changed after I was up to about change number 4. Good point about making a new file name.

Lots of good feedback on the circuit. It will take me a while to get thru all of that as I am unable to work on my circuit for the next week or so. I will get back at this some today, but then maybe not unitl January. Unitl then, Merry Christmas and have a happy new Year!

by Graubot
December 20, 2012

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