| Electronics > Beginners |
| IR Remote Frequency? |
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| jwhitmore:
Hello all, I'm trying to re-purpose a handheld IR remote control for another function and wondered about the IR Receiver selection. I stuck a scope onto the IR LED's of the remote and they seem to be transmitting at 31.25KHz I have an IR Receiver in my parts bin, but it's a 38KHz :( I looked at its datasheet and that family of IR Receivers has a 30KHz and 33KHz part. I've looked at a number of parts but that seems to be the standard 30 and 33KHz. So what part do I need I guess, a 30KHz or a 33KHz? They've probably got a band pass in there so perhaps either would do but I assume my 38KHz is no good for this remote. Any help would be very gratefully received |
| jwhitmore:
I just had a thought that I'm looking at the wrong number. I looked at the voltage wave form being sent from the uC to the IR Transmitter LED and that's being driven at 31.25 KHz. I just had a thought that perhaps the Frequency listed for an IR Transmitter or Receiver it's the frequency of the light that's being talked about? I might have this totally wrong, so then it gets even more difficult to talk to communicate with the remote. :( |
| oPossum:
CIR is usually 940 or 950 nm. 31.25 kHz is a rather unusual carrier frequency. 36, 38, and 40 kHz are the common ones. The only CIR receiver I know of that will explicitly work at 31.25 kHz is the Vishay TSMP1138. https://www.vishay.com/docs/82484/tsmp1138.pdf |
| Brumby:
The frequency of infrared light is much, much higher. For a 940nm wavelength, this works out at roughly 318928146808.5 kHz - or close to 319 THz. FYI - While you will not be able to see IR light directly, every phone camera I have tried IS. So, if you ever want to check the IR signal is being transmitted from your remote, just fire up your phone camera, point the IR emitter at the camera and press a button or two. |
| soldar:
I checked one of my remotes. The IR has a base carrier frequency of about 37 KHz and is modulated with a series of 27 pulses which take about 240 ms. Different keys send different combinations of pulses. The three pin IR receiver already detects the signal and outputs the modulating pulses, not the carrier. Neat. |
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