View Full Version : Propeller Freq Synth Output

09-09-2007, 04:26 AM
Is this correct ?? or is something drastically wrong with my hardware.

There is a spin file provided with the software named "CTR.SPIN".· It is a very basic·program to uses the 2 counters in a single coge to provide a series of pulses from specific pins at a fixed frequency.·· I modified it only to introduce a 180 degree phase shift in the two outputs and to use the·BAR LED·(P16 and P17)·on the PROPAMP board. I then looked at the 2 outputs on an oscilloscope.· A bmp file of the ouput is attached.· Since I am currently interested in the 1 to 200 HZ output range, I set the frequency the frequency of interest to be 2 HZ.· Indeed, I do receive a 2 HZ output with one output shifted by 180 degrees.· Just what I was looking for.

Unfortunately,· I don't get a·well defined square wave,·Indeed no square wares at all,·just a series of capactive charge/discharge (undershoot/overshoot)curves with the proper frequency.· Not what I was expecting or wanting.· I was wanting to use the·propeller·as a programmagble signal generator for·input to other circuit testing but I can't do that with the signal it produces.· I removed the BARLED from the circuit just to be sure it was not influencing the ouput. Thre was no change.

So, Is this the correct?? is the hardware malfunctioning?? Is there a way around this problem??

Post Edited By Moderator (Joshua Donelson (Parallax)) : 10/23/2009 4:46:52 AM GMT

Graham Stabler
09-09-2007, 04:56 AM
Make sure your scope is in DC coupled mode for this low frequency, that may help.


09-09-2007, 04:57 AM
Well, this is the characteristic answer from a high-pass filter to squarewaves.
So you have a series capacitor somewhere in your line... RC is around 0.1s

09-11-2007, 09:08 AM
This is what happens when you do software too much and get away from the hardware.· DUUUUUH.......AC coupling on the scope will do it every time. Sorry for the bother, thanks for the help.

Graham Stabler
09-11-2007, 07:17 PM
What I didn't mention was that I did the same thing the day before :)