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Registered Member #97
Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61
My goal is to look at the IR output of a TV remote. I built the attached circuit. It does give me an output, but as far as I can tell there is no difference between any of the functions, volume, the number 1, power, etc. I am using a radioshack phototransistor. So is there a better circuit or a better phototransistor that I can use? Any suggestions?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Scope usually isn't going to trigger well with remote signal, with resolution high enough for you to see the data.
In lack of DSO, just connect the phototransistor over your soundcard input, and record with adobe audition or etc. Bitstream is very nicely visible in each burst.
Registered Member #97
Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61
Alright I figured out why I wasn't seeing any change inbetween different functions. TV remotes send out the information signal, like volume up, followed by a signal that tells it to repeat. You can verify this by covering the LED, holding down the volume up button, and then uncovering the LED nothing will happen.
I took apart a remote, removed the LED, and attached leads to where the LED was connected. Looking directly at the output on a scope I can see the signal that contains information, but then all I see is the repeat signal.
I don't have a DSO so how exactly do I attach either the previous circuit or the output of TV remote to my sound card input. Do I just connected it to my microphone input and if so do I have to worry about overvoltage?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I don't have a DSO so how exactly do I attach either the previous circuit or the output of TV remote to my sound card input. Do I just connected it to my microphone input and if so do I have to worry about overvoltage?
You don't need divider, external supply or anything.
Just connect the phototransistor between GND and input, just like electret mic would be.
Then just point the remote at it from distance of few cm and you can get a nice record in audition. I did that and works well.
If you really want to probe the input directly you'l have to use some 1/3 divider on IR led and connect it between soundcard ground/input.
Registered Member #97
Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61
Thank you guys for all of your help.
Just a few more questions. Question 1: If I wanted to build a giant superpowerful TV remote would these work?
Here is the only datasheet I could find. Their peak wavelength is 940nm, but how stuff works says that TV remotes operate at 980nm. Then again the IR led I have from radioshack also has a peak wavelength of 940nm and that works on the TV. So..
Question 2: What wavelength should I shot for
Question 3: What would be the best way to drive 10-15 of these LEDs off of a few AA's? Just an appropriately sized transistor?
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Phototransistor and TV remote
