Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!zardoz.cpd.com!dhw68k!felix!dennisg@felix.UUCP From: dennisg@felix.UUCP (Dennis Griesser) Newsgroups: sci.electronics Subject: Re: IR Reception - Modulation and Quality Message-ID: <159639@felix.UUCP> Date: 26 Mar 91 00:35:17 GMT References: <2766.27E40773@ofa123.fidonet.org> Sender: daemon@felix.UUCP Reply-To: dennisg@felix.UUCP (Dennis Griesser) Organization: FileNet Corp., Costa Mesa, CA Lines: 41 On Rodentia writes: R> With that, I can hear my remote from about four feet away (with a R> fast dropoff in amplitude). In fact, I get similar results if I R> remove the power from the receiver. My TV definitely can handle R> eight feet plus, so what are they doing better? In article <2766.27E40773@ofa123.fidonet.org> rick@ofa123.fidonet.org (Rick Ellis) replies: E> They modulate the IR at about 40khz (usually) and use a very narrow band E> detector. The detectors ring badly but are good for detecting the leading E> edge of a burst. OK, so let's talk detector quality. Specifically noise immunity. Like half the people on the net, I have been experimenting with the IR detector module made by Sharp, sold through Radio Shack. There are occasional bursts of optical noise that fool the receiver module into believing that it has seen an IR signal. I can deal with this. The incidence is low. The big problem is electrical noise on the power supply! I have a goodly amount of X-10 stuff in my place. Some of the transmitters are stronger than others. Whenever I press a button on one of the stronger transmitters, the IR module reports seeing a pulse. I have yet to analyze the duration and pattern of the signal. It merely shows up in the pulse-trapping setting of my logic probe. Obviously, some of the 121 kHz carrier of the X-10 leaks through the power supply that I am using for the IR module, and fools it into believing that it sees an optical signal. I have verified this by operating the IR module from batteries; the noise problem goes away. This is a bit spooky, since I get the IR module power from the AC line by running it through a transformer, full-wave filtering it, smoothing it with several hundred microfarads, and passing it through a 3-terminal regulator (LM 309K). Of course, I have a few 10 mfd tantalum caps sprinkled around the digital section, and on the order of one .1 mfd monolithic per TTL package. And did I mention the Corcom line filter in the primary of the power supply transformer? Still the noise gets through. Any ideas, gang?