I bought my wife a Roomba for Christmas. The one I got has one 'virtual wall' with it. The virtual wall allows you to place it inside a doorway, for example, and it emits an IR signal the the machine won't cross - you can stop it from going into the room. You can buy more of these virtual walls, but, of course, I would rather build one.

In searching robotics forums, it would appear that the virtual wall is a 38Khz carrier, turned on and off at 1ms intervals.

I'm just starting to experiment, so I may be WAY off here - but I just used an 18F2550 that I happen to have breadboarded, right now, and did the following:

Code:
HPWM 1, 254, 38000
When I put the scope on it, I got 38KHz (a little over, actually) and a period of 26uS (38KHz is actually 26.3uS). So probably, that will be close enough to work - I can't imagine the receiver on the robot is too fussy, but I'll have to try it.

Then, to get the 1mS on and off, I decided to just switch the pin from output to input and back again. Not sure why I have to use 500uS on one pause and 1000uS on the other pause, but the scope shows what I wanted for times. So I came up with:

Code:
MAIN:
	HPWM 1, 254, 38000  
        pauseus 500
        TRISC.2 = 1
        pauseus 1000
        TRISC.2 = 0
	GOTO MAIN
And the attached picture is what the scope shows (not an expensive scope by ANY means). My question is after the image.

Name: IR1.JPG Views: 1195 Size: 86.6 KB

Any idea what that slope is as the port is switched from output to input? Any way to get rid of it? Or am I just on the wrong track here?

Thanks

Andy