Tom Metro wrote: > stuart wrote: >> Humm, but I can't find what I'm thinking of (using a 74CH00 chip, >> half as a monostable multi vibrator operating at 40KHz and the other >> half to help gate the signal). > > That might be because the modulation required by some devices may be > more sophisticated than simple asynchronous amplitude modulation. Some > devices may require frequency or phase modulation, or AM that is > synchronous with the carrier wave. > > Although according to: > http://www.linux.org/docs/ldp/howto/Infrared-HOWTO/infrared-howto-c-lirc-irda.html > > "The IrDA Physical Layer is totally incompatible with the DASK > modulation used in IR remote controls."
Yeah, if I recall right ... irda (like on a Palm Pilot) is a bunch of pulses where I think 0s and 1s are marked by either having or not having a pulse. Ask is more like pulses of ~40KHz modulated light. I would guess irda is generally faster but only works over a short distance whereas ask is slow but can be filtered (@ ~40KHz) so can work over longer distances. (The accuracy of the above is questionable as I'm being lazy and not looking anything up. (i.e. [needs citation])) > I assume the D in DASK stands for digital. Amplitude-shift keying (ASK) > is described here: > http://en.wikipedia.org/wiki/Amplitude-shift_keying > > and in its simplest form would be achievable with the circuit you describe. > > This site: > http://www.zen22142.zen.co.uk/Circuits/Interface/mod_det.htm > > which has a schematic for building an IR receiver for use with a scope > for observing remote control signals (most likely overkill, and with a > decent scope you'd do fine with a photodiode or a phototransistor and a > few components), also backs up the idea that the modulation is simple AM. > > That site also has a pile of remote control extender circuits: > http://www.zen22142.zen.co.uk/Circuits/Interface/rce.htm > > which could be adapted for use with a PC. > > >> Instead I found things like: >> http://www.lirc.org/improved_transmitter.html >> ...which need each pulse controlled as you said above. > > And half of that circuit is just trying to achieve creating a power > source for the LEDs from the serial port. If you wired up a power > supply, you could probably do it with half the components. Yes, I noticed that too. Consider that if you did load up the Palm Pilot w/the code to produce ASK that (reportedly) you need to be w/in a few feet of the receiver for it to work. So having enough power is important. (Point your *digital* camera at your remote control. It's quite bright.) This all begs the question: "At that distance, why not just reach out and use you hand?". >> ...I'd search the hifi-remote.com web site. Chances are very good >> that someone has already captured the codes you are interested in and >> published them... > > Agreed. I wouldn't recommend using a scope to reverse engineer the > actual codes. I was just suggesting using it to verify that the general > signal characteristics, such as modulation frequency and type, match > between the original remote and the simulated remote. > > -Tom I think it's time (where does that stuff come from any ways?) to try some things out on the work bench. Regardless, I think I'll add some of your links to the hardwarehowto along w/some possible mvpmc enhancements. I've always thought an IR blaster on the mvpmc box would be nice (i.e. Get rid of the TV remote!). ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Mvpmc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/mvpmc-users mvpmc wiki: http://mvpmc.wikispaces.com/
