AVR interferes with IR decoder

[Electro Tunes]

I don't know the technical term for this phenomenon. It goes like this:

An IR decoder is connected to V, ground and it's signal pin a LED. Also, an AVR micro is connected to V, ground, and one of it's pins to another LED. The micro is programed to oscillate that pin at 38 KHz, which is the carrier frequency the the IR decoder is designed to decode.

The phenomenon I get is that the IR decoder always indicates a signal.

I think my circuit lacks a capacitor somewhere. I've put capacitors everywhere but it didn't help. Sometimes the IR decoder calms down and behaves but this is rare.

What's going on here?

 

[blueroomelectronics]

Post a schematic. Most 3 pin IR detectors require a decoupled 100ohm, 4.7uF supply. Some have built in pullups - some don't. It's all in the datasheet.

 

[neophyl]

This may sound a little stupid but is the led thats ocillating at 38khz anywhere near the ir detector ? Ive done a fair bit of IR work and if the led is a red led then theres usually enough light in the near IR range to trigger the ir detectors. Before trying anything else completey block the output of the led with some ir blocking material to rule out if your pulsing led is setting the detector off optically.

 

[Electro Tunes]

neophyl, this doesn't sound stupid to me , however, the LED is yellow and I also tried to block the receiver.

blueroomelectronics, unfortunately I don't know the P/N of the receiver. I attached a snapshot of my breadboard setup.

 

[Nigel Goodwin]

From that picture you appear to have none of the required components - have you never heard of decoupling capacitors?.

Like Bill said above, it's ABSOLUTELY CRUCIAL that IR preamps are decoupled with a series resistor and parallel capacitor - and close to the receiver. Check the hardware from my PIC tutorials.

 

[blueroomelectronics]

Add to that it's got to be an IR LED and the output of the IR detector can only pull to ground it won't source much current (assuming it's got a pullup resistor) Try using a TV remote and skip the AVR to see if the IR can see the TV remote.

 

[Electro Tunes]

Nigel, can you provide values for the series resistor and parallel capacitor? I couldn't find any example of "decoupling capacitors" at your site.

blueroomelectronics, right now I want the both "sub-circuits" (detector+AVR,led) to coexist... When they do, I will replace the LED with an IR LED. The receiver works find when the ARV,led aren't there, I've tested with a TV remote.

 

[Nigel Goodwin]

Nigel, can you provide values for the series resistor and parallel capacitor? I couldn't find any example of "decoupling capacitors" at your site.

In the tutorial hardware