Debugging USART using Saleae logic probe

[ozarkshermit]

Not related totally, but I absolutely LOVE my Saleae Logic.

I just used it again today to determine some Infra Red codes from a remote transmitter. I don't use it all that often, but it has helped solve some otherwise very troublesome problems.

Ken

[Demon]

Neat. Can you provide details how you did it?

It's one of those things on my To Do Whenever list.

Robert

[ozarkshermit]

Sure - not much to it actually.

What I want to do is determine what the hand held IR remote sends to one of those programmable , scrolling led
signs that you can put in the rear window of your car, or whatever. All I I want to do is to start any already
programmed message, using a PIC instead of the hand-held remote.

I breadboarded a TSSOP type infra red receiver, and connected a single Saleae channel to the output. Then just
pushed any button on a hand-held TV remote for a moment, and captured the pattern. From there it was easy to
duplicate the pattern, using a short program turning a single output off and on, using pauseus delays to match
what the remote sends out. The PIC output pin will be connected to an IR transmitter, to "talk to" the sign.

I have written a simple test program to do this, coupling a PIC to a simple IR transmitter.

I haven't finished this project yet, still waiting for the scrolling sign. However, I have been able to easily duplicate
some transmission patterns from a TV remote, so the next step should be relatively easy. I only plan on "cloning"
a couple of different transmissions, not the entire keyboard, although with enough patience that could be done.

I know there are some perhaps simpler hardware solutions to this, to "learn" what the transmitter sends out, but
this is was a drop-dead simple answer (for me).

[Demon]

I must have several obsolete remotes lying around in the basement. What exactly do I want to scavenge out of them? Is it only that clear LED-looking-thing that is necessary?

Robert

[ozarkshermit]

Robert:

Any of the old remotes would probably work to experiment with for a transmitter. They would all have the related protocol for whatever device they were controlling, but that wouldn't matter, if you just want to prove out the method you use to capture the output on the Saleae. Yes, the LED is part of the transmitter.

You need a IR receiver as well. Some folks just use a photo transistor, I would recommend a good IR receiver, since they have additional features built in. I am using a TSSOP 32338, but there are a multitude of receivers available.

Here are a couple of good links on this subject:


http://learn.adafruit.com/ir-sensor

http://www.robotshop.com/blog/en/bui...e-decoder-4254

http://www.pic-tronics.com/IR-Transm...d-Receiver.php

If you want, I can post a couple of screen shots of my results, first a sample of an actual transmission from a TV remote, and then one of the duplicates using a PIC to output the pattern.

Ken

[Demon]

10 years later and I'm still loving my basic Saleae logic probe. It was invaluable to help me figure out what's going on with these encoders.

- noticed jitter on 2nd circuit on chinesium double encoder when I move other shaft,
- spent all day going through my code, turned out the 2nd channel is also dropping pulses.

I can't imagine life without it (top pair at PIC, bottom at encoder pins).




Pulses are inversed because I use a 74HC14 after Bourns debounce to clear up signal.

[richard]

the saleae can just as easily miss pulses as anything else if the sample rate is too low, re's need a high rate i use 12-16 Ms/S to be sure