Flashing a LED to the response of a TV remote??

[IsaacHayes]

Silly project #2983983. I want to make a highpower Orange 50ma 10mm LED turn on in response to light picked up from the TV/Stereo remote..

It will run off of 3xAA. I'll have some blue leds too but the Orange will be the one switched. I want to set it on top of the TV and have it swtich the LED on each time it receives the IR. So you can see the different frequencies of the buttons pressed when you change channels/etc.

What do I need to do this? An IR receiver diode at radioshack, and some sort of transsistor? What kind and how to wire?? Will this work at all?

Thanks in advance...

 

[Doug Owen]

I've messed with this some, using IR phototransistors. At least one came from RS. The one you want is molded from very dark red plastic (almost black), some look like LEDs.

There is always some IR about, but the remote is pretty bright. What you 'see' is the flashing, but what is 'on' and 'off' in absolute terms is not well defined as at longer ranges the flash can be dimmer than the background is in other situations. The solution I've used in the past is to AC couple the signal from the phototransistor to an amplifier, boost the 'flash level' a bunch and peak detect the result. It's a (fairly) simple matter to then build a (switched) current driver to drive an LED with the recovered signal.

While I've always ended up driving another IR LED for 'relay use' in another room, I've used a visable LED in testing. I've also watched on a 'scope' (oscilloscope) the data stream. It's far too fast for your eye to see much difference between buttons in general. However, some (like say volume up) buttons transmit continuously and some (like say a number) may flash their pattern only once on some controls (some just repeat until you release the button no matter what the use).

While I've never tried for ultra low current in standby, I think it'd be very hard to get it low enough to make running on a battery practical.

Doug Owen

 

[IsaacHayes]

Hmm.. so switching a transistor isn't practical enough because the signal is so weak eh? I too have thought about using a relay system like you talked about if I were to put say a DVD player in a trunk of a car, and use the remote aimed at the dash..

There was a circuit I built from a radio shack book a long time ago like when I was in gradeschool. You could shine a Remote at it and it would power a speaker and make different tones for the different buttons.

Another behavior of my Awia remote is that it sends a start up signal, then following a constant signal. This happens when you press and hold the volume, it will keep going. But if you aim away from the unit when you first press it, and then move it into view, it won't start moving the volume....

 

[Doug Owen]

[ QUOTE ]
IsaacHayes said:
Hmm.. so switching a transistor isn't practical enough because the signal is so weak eh? I too have thought about using a relay system like you talked about if I were to put say a DVD player in a trunk of a car, and use the remote aimed at the dash..

There was a circuit I built from a radio shack book a long time ago like when I was in gradeschool. You could shine a Remote at it and it would power a speaker and make different tones for the different buttons.


[/ QUOTE ]

Yup. You can use a phototransistor up close, but it rapidly dies when you back off.

You can probably *hear* the bit stream, but you can't see stuff that fast. You don't see the flicker on TV at 30 frames a second, you'll never see a hundred or thousand times that.

Yes, treat it as an audio signal, *amplify* it, and use a peak detector to drive a LED rather than a speaker.

Doug Owen

 

[PhotonWrangler]

I've connected a small, low-voltage green led directly to the TTL output of one of those RS IR decoder modules. Not terribly bright but it worked.

The thing is that the IR light is modulated at around 38hkz, so I doubt that you'd be able to tell the difference between individual IR commands.

A quick way to verify this - most CCD cameras can see into the near-IR region. Find a video camera (or a webcam) and point your remote control at it while watching the camera's output on your TV or computer. You'll be able to see the flashes quite clearly.

 

[IsaacHayes]

I wonder if the circuit lowered the freq before playing it through the speaker.. 20khz is the limit of most human hearing....

I think I still have it put together on an old breadboard...

 

[georges80]

You can buy 3 pin devices (digikey has them) that are specifically designed to remove the 36/38/40khz carrier from the remote control IR stream. You will get 1's and 0's out of the output. PNA4602 (search on digikey) is one such part. Not sure what your 'project' is exactly for, but you will find different remotes use different carrier frequencies AND different protocols. I've worked with a few of these detectors and protocols at work.

george.

 

[IsaacHayes]

Just wanted something neat that would light up or strobe when it picked up IR. A toy... or a use for my 10mm orange led...