RF and Sharps not playing together?
March 20, 2009
With my new found osilloscope skills and a little tinkering, I think I have found the noise. As far as I can tell, it is all on the ground. Here's what I did:
I wired the RX unit to a different picaxe on a test board using an isolated (seperate from walter's batteries) battery pack. Running a test transmit/receive program I brought this test board over to Walter to check for RF noise. I even went as far as phyically wrapping as many of sensor and power wires around the antenna. I got 100% clean data. Second, again with the same battery pack on the test board, I connected the ground of the test board to Walter's ground and the signal wire from the RX to an input pin on walter's brain. Boom went the dynamite. Zero, no data. Again, unplug the sharps with this "shared ground, different batteries" set-up and I get 100% data. This would lead me to believe all the crap is on the ground wire. This leads me to a question: I remember (vaguely) back from my car stereo days something called ground loops. Also, I went to the Texas Instraments website and searched for isolators where I found some sorta chips that mentioned isolating grounds --I really didn't understand the data sheets but I did like the phrase "isolated ground". The question is, is there any way to isolate a ground? Can the RX unit continue to share the same batteries as are powering the sharps but somehow isolate the ground going to the RX unit from them? It seems this sharp noise is not affecting any other systems on Walter... Yet.
I am hooking up my new RF RX unit to walter and have found a wierd thing...
Sharps: Just the regular old Sharp IR distance sensors
Now, each sharp has a .1uf cap across + and - to deal with some noise I had earlier -they work perfectly now. With all 4 plugged in to the adc inputs of my 40x1, the receiver simply does not work. I have tested it's output with a speaker and indeed it is spitting out data. However, the picaxe does not recognize anything going into it's input pin. I am using debug and it simply sits there waiting and waiting. Now, when I unplug the sharps, all is well and I am getting 100% of data coming through. Even better -as I plug the sharps back in, one-by-one, I can watch the debug window count slower and slower until it stops entirely. I unplugged the sharps and replaced them with just a cap (to see if it was the caps causing the problem) and it seems that is not the issue. It is not a code problem as I am just using:
Any thoughts, you electronics genius-type guys got any ideas?
Oh, there is plenty of power, all is getting a clean 5v from a regulator. --Checked it with a measure-thingie and the sharps are not stealng anything.
Info for Frits and the Poor-man's ossiloscope...
Included, as you will see is the MP3, here are the screen shots:
No Sharps plugged in -Serin working great, no data lost
One Sharp Plugged in: Debug working, serin working but very slow
Four sharps: Debug stuck waiting -serin not serin'ing
Coming out of TX: