Detecting IR frequencies

Most remotes are at 38 kHz.... See

for an interesting read on remotes. There are directions on the site for building transmitters. It's not trivial - but it is fun.

38 khz? Are you saying these remotes run off AM not FM?

I don't know --- all I know is that is stated frequency of the receivers I use and they work.... Check out vishay 1738

- I have made several of these and they work with common IR remotes.

--Yan

Why would you get that from what he said? It could mean a carrier frequency for an AM signal, or the center frequency for an FM signal.

Besides, if it was amplitude modulated, more likely you'd just see a modulation of the IR LED, rather than have a subcarrier feeding it. But there are very good reasons for not doing it that way, because it will mean the circuitry is more likely to be interfered or confused with by light levels in the room (or for that matter random light levels could cause the unit to change channels). Finally, when you start amplitude modulating an LED, you can't set things for optimum performance.

Which means that it will likely be FM, because it doesn't matter if you directly modulate the LED or modulate a carrier that feeds the LED.

With FM modulation, the feed to the LED is constant, hence it can be set for maximum output.

Michael

The method of modulation does not depend on the frequency. You are probably thinking of commercial radio where FM radio is around 100MHz and AM is ~100kHz.

Most remote controls have very simple modulation. There is a carrier, which is probably around 38kHz. This carrier is switched on and off (at a frequency much lower than 38kHz) to give a pattern of pulses which corresponds to the button you pressed. I'm not sure how you would find this pattern unless someone else has done a similar project - try a Google search.

Gareth

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gareth.harris

I would hazard a guess that the motion detector uses "Passive IR" or "PIR" detection, which is essentially a heat sensor that registers the change in heat in its field of view and sounds an alarm. This is the principle that the vast majority of home security motion detectors, automatic lamp sensors, etc. employ.

If my assumption is correct, there's no emitted IR signal to detect. The Wild Planet box is simply a sensor and makes noises when it detects motion.

I'm basing this on what I found at this link:

TJL

the frequency of the IR is the leasst critical thing, what you need to track down is the exact IR pulse sequence the remote sends.

if you don't want to buy an IR detector open up the remote and attach an apropriiate device to the LED and record the pulses it gets.

Bye. Jasen

No he's wrong they operate at around 320THz :)

the IR beam is amplitude modulated (well pulsed would be more acurate) at around 38KHZ and the 38KHZ itself is pulsed to send a digital signal coressponding to t he keypress etc that the remote wants to send.

there may be remotes that do FSK or PSK on the 38KHZ "carrier" or use some other frequency...

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Bye.
   Jasen