Get IR Signal and its strength

Question

Using an IR sensor, how can I get and decode signals from other IR devices? I've seen the IRRemote library and its forks, but it doesn't fulfill my second requirement which is that I need to be able to tell the signal strength of the IR signal.

In addition, do I have to use a higher-end TSOP module? Or could I just use one of these?

Thank you!

Answer 1

An IR signal is modulated. To understand the data you need to demodulate the signal. The simplest way is with an IR receiver module. However they condition the signal into a digital signal - it's impossible (on the majority of modules) to get the signal strength.

The devices you link to are IR Photodiodes. They form the optical receiver portion of the IR modules. You need to couple them with some form of demodulating system - either in hardware or, if your MCU is powerful enough, in software. However, you can get at the raw analog voltages that the photodiode generates to get a signal strength value.

So you have either an easy time of it but no signal strength, or signal strength but a very hard job of interfacing.

So why not take the best bits of both? Use an IR module to demodulate the signal and give you the data, and next to it use a photodiode and op-amp (to boost the tiny signal) to give you the raw optical intensity? Yes, it would cost you more, and the circuitry would be more complex, but it's really the only way that you can do it without using specialist modules.

But of course, it begs the question: why do you really want to get this kind of information? Of what use can it be? The "signal strength" is of little benefit since there are so many factors that influence it - incidence angle, distance, transmitter battery voltage, etc.

• Ben Gubler: I want to be able to estimate distance. I was hoping to be able to create something like Pololu's IR Beacon because to buy one is way out of my price range.
• Ben Gubler: Do you think I could build one with 360 degree vision + demodulation for under 5,ドル or is it hopeless ;)?
• Majenko: If all you care about is the distance and there is no data in the signal then yes, you can just shine infra-red light at a photodiode and the generated voltage will be proportional to the distance. It's crude, but works.
• Ben Gubler: But I probably couldn't with a signal?
• Majenko: As in the output of a remote control? Not easily, no.