38 KHz IR xmtr

Interesting question.

Remote controls are all based on microcontrollers (possibly 4 bit, mask programmed), so they don't need it. Since this is true of the general marketplace, I guess that might answer your question.

You can make your own from a 555, R and C, so it's not hard otherwise.

Tim

-- Deep Friar: a very philosophical monk. Website:

Have a look at this - page 94 and 95 might be of interest

Well, yeah, but these aren't used by hobbiests either. That's what I'm thinking of.

=A0> Since this is true of the general

No, not really. How big is the hobbiest market? Since no one's actually *bothered* to make one of these purpose-specific chips, it's hard to say what the penetration into the commercial market would be as well.

But I thought that's what the whole idea behind the PIC was. Now you want me to create an analog device using about six (or so) discrete parts when one digital part would do it? I specificly remember Don Lancaster writing in one of his columns years back about how he would never use a 555 again. Well, Don, am I right? Is this the equivalent of a 3-pin regulator, or just wishful thinking? (and you can be an extremely harsh but extremely realistic critic)

d

That's a little beyond what I was looking for, but nice to know. I wasn't looking for commands, just the modulation of the signal. In playing around with photodetector circuits recently, it would have been really nice to be able to use the IR modulation detectors available instead of just a simple phototransister. Although there's no actual data going over the beam, its a lot easier to pick out of the background.

There are no products built for "hobbiests".

Just hobbyists using standard products.

I just don't understand what your asking for.

hamilton

The combined functions of 38 kHz oscillator, NAND gate, and LED driver, is presumably what you're asking for? Gated CMOS oscillators (crystal clocks with an 'enable' pin) come close, but that 38 kHz frequency isn't a standard in that form factor.

Any old oscillator you can trim, and two diodes and a transistor, is all that's required. Commercial remotes use higher frequency clocks and divide down, and that's how a PIC solution would likely be designed, too. For best current to the LED, the PIC solution still wants a transistor.

If you're making your own transmitter it looks like the PIC is a good way to go. I built a 'transcoder' several years back to receive a code, change it and re-transmit it. Receiving is easily done with many different chips. I was using a Freescale (Motorola) processor

68HC908JK1 or JK3 device and while transmit maybe can be done totally in software, it seemed a little too tricky so I added a 22V10 GAL as a counter/gate (modulator) using a 32MHz oscillator. This works well for line powered but would be bad on batteries. Since its so easy to read / decode a remote, why don't you just buy a cheapy universal remote and just build the receiver section? These are very easy to interface. The demodulation is done for you and all you have to do is run a timer and count off pulse widths. I can give you known working Moto code. The assembler is a freebie from P&E microsystems and the programming module is very inexpensive to build. Your PC will require a plain vanilla COM port to talk to it. The third link shows a schematic of the programmer. Mine's still 'built' on proto board.

SET=3DDocumentation

The schematic is missing the RS232 receiver chip. Moto used to make one but apparently discontinued it. It's a good old MAX232. They tap a little of the +10 to make the programming voltage. If you want to go this route I can email you the PDF that still has the RS-232 chip in it. You'll just use the MAX232.

G=B2

Sorry about that Digikey link. Try this one

-ND

They have MANY more types.

G=B2

Why don't you just use an old remote control?

Ok some of them tend to have large gaps between repeats so might reduce your latency slightly as you have to allow these. If you were really lucky you might find a remote with a test mode that outputs carrier wave only.

-- Tony

Actually they do make them. They are just seriously hard to find for the uninitiated.