Stamp reading RC Receiver signal to servo

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sdobrowski
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Location: Rutherford, NJ
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Stamp reading RC Receiver signal to servo

Post by sdobrowski » Thu Oct 09, 2003 9:34 am

I am using an RC transmitter and receiver to control a BASIC Stamp controlled robot. The receiver normally outputs the pulse streams to the servos, but I have them going to inputs of the BASIC Stamp instead.<p>I know the Stamp can easily read the pulses put out by the receiver with the PULSIN command and this works fine. But when the only "load" on the receiver's pulse output is the Stamp's input, the pulse stream seems to be erratic. When I connect a servo and a Stamp, then the pulse stream calms down.<p>My question is what kind of "load" do you recommend on the receiver output's when they are only going to the Stamp's inputs.<p>Thanks, in advance, for your help.
Stan

dyarker
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Re: Stamp reading RC Receiver signal to servo

Post by dyarker » Sat Oct 11, 2003 10:55 pm

I've never worked with servos (yet), but I recognize the symptoms.<p>A micro-controller input has a very high impedance (probably CMOS). Add a resistor from signal line to ground, to increase the load on the RC receiver to something closer to what it expects to drive. I'd start at 10K Ohms.<p>It may like a little capacitance too. Start at about 0.00047uF, or smaller. The idea is to control ringing, not to lengthen the pulse's rise/fall time too much.<p>Without servo specs and some math, it would help if you had an oscilloscope and 10X probe to monitor the signal as changes are made.
Dale Y

Megadan
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Re: Stamp reading RC Receiver signal to servo

Post by Megadan » Sat Oct 25, 2003 1:37 am

A 10K resistor to ground will deal with this open loop capacitance nicely. I used a Basic Stamp to read my Futaba R/C receiver signals in 1996 - but back then the receivers generated a real 5 volt square wave. These days it's closer to 3.3 V - so beware!<p>Dan
Dan Danknick

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