How do IR remote controls work so well?

On Jan 21, 11:09=A0am, Kasterborus wrote: > I've been experimenting with detecting reflected laser pulses in the > 532nm (visible green) wavelength. By modulating the pulses and tuning > a receiving circuit I've been able to get the detector to work over a > distance of several feet in a darkened room. >

The modulation is a big part of it. The remotes I've worked with (Samsung and Sony) both send 32 bits total and the last 8 bits are sent twice, the second time inverted which helps data verification. Both remotes continously repeat the 32 bit sequence as long as a button is held so there's a good ghance some af the commands will get through.

GG

I guess it depends on the detectors. Some may filter out other frequencies.

For example, the TSOP11xx set of photo modules are very good at filtering out light at other wavelengths. That is how IR works so well for TV, for example; they filter everything except the 950nm IR between 900nm and 1um down to -6db, and then only respond to modulation frequencies between 0.95 and 1.05 percent of the target modulation (ie, 40k).

See the figures in this data sheet:

Again, the detector is tuned to both the frequency of light, and also to the modulation frequency of the signal.

They have a IR passive filter that helps reduce non IR light . also, the modulation scheme has a lot to do with it.

Normally common mode input receivers are used with capacitor offsets on one input so that the DC component can be nulled out while the AC component will be visible with high gain.. they may even have a band pass filter after that stage..

This means, your modulation scheme must use a steady stream of pulses for 1's or 0's.