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RF and Sharps not playing together?


***Update 3.21.09***
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...

RX unit: http://www.rentron.com/remote_control/RWS-434.htm

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:




goto main

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:





Osiloscope_mixdown.mp32.11 MB
No_Sharps_Plugged_in__mixdown.wav3.22 MB
Two_Sharps_Plugged_in__mixdown_3.wav3.7 MB
four_Sharps_Plugged_in__mixdown_3.wav2.85 MB
Audio_Ossilo_TX_mixdown.wav3.55 MB
TX_RX_Stereo_NOTWorking_mixdown_2.wav2.22 MB
TX_RX_Stereo_Working_mixdown.wav3.41 MB
TX_RX_One_Sharp_plugged_mixdown.wav2.9 MB

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Yes, rik...

those are the sharps I am using, but again not for wheel encoders but rather for actual distance sensing arond walter's chassis. 


That's a pretty good one, frits... Gotta give you that one. 

These are the wheel encoders... and as I remember, yet another shout-box episode...

GP2Y0A21 http://letsmakerobots.com/node/3172 ?

(up to 80 cm, 32 inch)



oh never mind .........

what's the use 8-p


So I got to thinkin' which is usally a problem but worked this time. I thought to myself, "what are the sharp sensors really for?" It was then that i realized that the sonar is really taking care of about 90% of the navigation and the 4 sharp sensors were just back up and to take care of the couple "blind spots". For example: 2 of the sharp sensors are facing directly to the outside of the frame, 90 degres to the direction of travel and serve only to keep walter off of the walls if he is "drifting" that way. These 2 sharps are set at about a 2" distance reaction. LMR to the rescue! I seemed to remember a couple people having built sensors (a crap-load cheaper by the way) to address this issue. I think one was named after a dog and the other comes from some guy from Australia! So I got to lookin'. Seems that oddbot has one with a 4-6" range and not a single part that could introduce noise!!!

It also seems that some sarchastic Danish guy did the same...


I am back from Radio Shack...


In conclusion, Fuck the Sharps!! I have always said, you will not find a VW Beetle with a bad radiator or water pump...You know why? They don't have the damn things installed!!!!

Now, in terms of the last 2 sharps... These guys are on the front corners and face forward. Again, they just suplement the sonar so if the sonar is looking hard-left and turning to the right, Walter can know if he is "turning into a corner" ie turning into an obstical on his blind side. For cryin' out loud! If I can't solve this one with a little code or heavan-forbid just simply another sonar sensor, I might as well give up here.

So that's what I'm doin'. Parts make noise and refuse to play well with others... Fuck 'em, they gotta go. Unless someone comes up with some kinda of magic, 100% fool-proof way of supressing this noise I'm stickin' wit' it, yo!

Again, thank you for all your help, guys and... We'll leave the light on for ya.

I thought you used them as wheel encoders? Was that a different story? You still have those?

I both like your thinking and swearing and attitude! Progress is king!

I would create a filter for the sharps, but I have a deadline at work, so no time, but glad to know you are moving on!

(I know that nobody trust that I could actually make such a filter, but ..)

Hello CTC,

excellent, it is usually better to sep. the logic and drive power. And your using the big 7805 which is cool a good AMP; now what is the logic supply voltage (i.e bat) 7805's like a couple of Volts in hand (i.e. 7ish volts in) otherwise you can drop out of regulation when there is a little bit of a draw on.

When I talk PC CRO I am talking about the Audio Port approach which has been talked about.

If you can use the Poor Mans PC CRO to look at the ground and power rails for me (both sides of the 7805) with the Sharps in and out, also trace on the sharp pin (the one going to the micro.

This is a solvable problem, it will have a root cause, just need to exclude all of the possiblities!

 all the best