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'Connecting servos to a PIC'
1999\02\07@202933 by Steve Pillwein

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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

1999\02\07@210916 by dave vanhorn

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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" .

1999\02\07@221553 by Eric Naus

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Look at my schematic on my hompage http://webhome.idirect.com/~bine

Eric

1999\02\08@055302 by Andy Kunz

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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!

1999\02\08@110451 by Adam Bryant

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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_OUTspillweiTakeThisOuTspamFREESPACE.NET on 02/07/99 06:30:02 PM

Please respond to .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU

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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

1999\02\08@112223 by jcline

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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}

Jonathan
@spam@jclineKILLspamspamee.calpoly.edu

1999\02\08@120859 by dave vanhorn

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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.

1999\02\08@133628 by Andy Kunz

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>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!

1999\02\08@135944 by Alvaro Deibe Diaz

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Why the resistor?

-----Mensaje original-----
De: Andy Kunz <KILLspammtdesignKILLspamspamFAST.NET>
Para: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Fecha: lunes, 08 de febrero de 1999 11:57
Asunto: Re: Connecting servos to a PIC


{Quote hidden}

1999\02\08@140754 by Andy Kunz

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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!

1999\02\08@140806 by dave vanhorn

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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.

1999\02\08@200342 by paulb

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Andy Kunz wrote:

> If you can find a copy of the NE544 data sheet, it's all in there.

 Not on the web I suppose?  Certainly not NatSemi, SGS or T-I.  I
gather it's a bit old!
--
 Cheers,
       Paul B.

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