Post by thread:Connecting servos to a PIC

At 08:30 PM 2/7/99 -0500, Steve Pillwein wrote: >I am experimenting with controlling R/C servos with a PIC 16C84 >I have the timing for the PWM worked out (roughly), but I need to know > >if it's okay to connect the servo control line directly to a port pin >without >damaging either the servo, or the pic. > >Steve I've blown a couple AVR8515's that way, I don't know why exactly. A series 4.7k resistor seems to solve the problem. The timing is trickier than it looks. Some brands use 1-2mS others use 400uS-2mS There may be more variants, but that's what I've seen in servos I've bought in the last 8 months. It's a brand thing. I've got AVR routines at http://www.dontronics.com in the download dungeon "getting started" .

At 08:30 PM 2/7/99 -0500, you wrote: >I am experimenting with controlling R/C servos with a PIC 16C84 >I have the timing for the PWM worked out (roughly), but I need to know > >if it's okay to connect the servo control line directly to a port pin >without >damaging either the servo, or the pic. No problem, but I would recommend about 330 ohms instead of a direct connection. Andy \-----------------/ \ /---\ / \ | | / Andy Kunz \ /---\ / Montana Design /---------+ +---------\ http://www.montanadesign.com | / |----|___|----| \ | \/___| * |___\/ Go fast, turn right, and keep the wet side down!

Steve, I do it all the time. I use modified servos for robotics (driven directly from the PIC port), and I also recently made a 16C84 based V-Tail mixer for my Airtronics radio. I put the output signal of two channels of the R/C receiver directly into 2 PIC pins, then the output (mixed) signal to the servos from two more PIC pins. I've used several different brands of servos as well and they all seem to work fine being driven directly from a PIC. Adam spam_OUTspillweiTakeThisOuTFREESPACE.NET on 02/07/99 06:30:02 PM Please respond to .....PICLISTKILLspam@spam@MITVMA.MIT.EDU To: PICLISTKILLspamMITVMA.MIT.EDU cc: (bcc: Adam Bryant/PEAK/MOORE) Subject: Connecting servos to a PIC I am experimenting with controlling R/C servos with a PIC 16C84 I have the timing for the PWM worked out (roughly), but I need to know if it's okay to connect the servo control line directly to a port pin without damaging either the servo, or the pic. Steve

I have done the same. See my 'BiMo III' robot for cool things to do with extra servos, 3" tires, and a PIC16F84 (source and schematic). http://www.ee.calpoly.edu/~jcline/ee/ I've recently been experimenting with my servos again and have found >70Hz for the frequency to be too fast (cheap Hitec servos), and <30Hz to result in jerky movement. {Quote hidden}> > Steve, > I do it all the time. I use modified servos for robotics (driven directly > from the PIC port), and I also recently made a 16C84 based V-Tail mixer for > my Airtronics radio. I put the output signal of two channels of the R/C > receiver directly into 2 PIC pins, then the output (mixed) signal to the > servos from two more PIC pins. I've used several different brands of > servos as well and they all seem to work fine being driven directly from a > PIC. > > Adam > > > > > > .....spillweiKILLspam.....FREESPACE.NET on 02/07/99 06:30:02 PM > > Please respond to EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU > > To: PICLISTspam_OUTMITVMA.MIT.EDU > cc: (bcc: Adam Bryant/PEAK/MOORE) > Subject: Connecting servos to a PIC > > > > > I am experimenting with controlling R/C servos with a PIC 16C84 > I have the timing for the PWM worked out (roughly), but I need to know > if it's okay to connect the servo control line directly to a port pin > without > damaging either the servo, or the pic. > Steve > Jonathan @spam@jclineKILLspamee.calpoly.edu

At 08:10 AM 2/8/99 -0800, Jonathan wrote: >I have done the same. See my 'BiMo III' robot for cool things to >do with extra servos, 3" tires, and a PIC16F84 (source and >schematic). > http://www.ee.calpoly.edu/~jcline/ee/ > >I've recently been experimenting with my servos again and have >found >70Hz for the frequency to be too fast (cheap Hitec >servos), and <30Hz to result in jerky movement. That's interesting. I've experimented with the frame rate all the way down to zero here, and not had any trouble.. That would be a 1-2mS pulse followed by 8-16mS of quiet on each servo. Slower I agree, they start to act more like sloppy steppers than servos, apparently they react to each pulse and when the pulse stops, they just stop driving and idle where they are.

>Slower I agree, they start to act more like sloppy steppers than servos, >apparently they react to each pulse and when the pulse stops, they just >stop driving and idle where they are. That's exactly right. The guy who did most of the original servo design, Fred Marks, explained the circuitry to me once. It's pretty neat. If you can find a copy of the NE544 data sheet, it's all in there. Andy \-----------------/ \ /---\ / \ | | / Andy Kunz \ /---\ / Montana Design /---------+ +---------\ http://www.montanadesign.com | / |----|___|----| \ | \/___| * |___\/ Go fast, turn right, and keep the wet side down!

Why the resistor? -----Mensaje original----- De: Andy Kunz <KILLspammtdesignKILLspamFAST.NET> Para: RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU <spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU> Fecha: lunes, 08 de febrero de 1999 11:57 Asunto: Re: Connecting servos to a PIC {Quote hidden}>At 08:30 PM 2/7/99 -0500, you wrote: >>I am experimenting with controlling R/C servos with a PIC 16C84 >>I have the timing for the PWM worked out (roughly), but I need to know >> >>if it's okay to connect the servo control line directly to a port pin >>without >>damaging either the servo, or the pic. > >No problem, but I would recommend about 330 ohms instead of a direct >connection. > >Andy > > > \-----------------/ > \ /---\ / > \ | | / Andy Kunz > \ /---\ / Montana Design >/---------+ +---------\ http://www.montanadesign.com >| / |----|___|----| \ | >\/___| * |___\/ Go fast, turn right, > and keep the wet side down! >

At 07:55 PM 2/8/99 +0100, you wrote: >Why the resistor? So when things are plugged together wrong, it will not burn up the PIC. Andy \-----------------/ \ /---\ / \ | | / Andy Kunz \ /---\ / Montana Design /---------+ +---------\ http://www.montanadesign.com | / |----|___|----| \ | \/___| * |___\/ Go fast, turn right, and keep the wet side down!

At 07:55 PM 2/8/99 +0100, Alvaro Deibe Diaz wrote: >Why the resistor? Primarily ESD protection i think. In my case I was using an Atmel AVR8515, and had problems (dead chips) if I didn't include the resistor. The AVR will drive into a short to ground or VCC, so it's not a drive problem. I didn't analyze it thoroughly. It's a "Good Idea" anyway.