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PICList Thread
'[OT] PWM Servo Directions'
1999\05\20@205529 by David Olson

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I'm wondering of someone can point me in a PWM direction.

I've perused some of the archives and there's a lot in there on PWM and
Servo control however, either I don't get it or what I'm looking for is not
in there. Anyway, I'm looking for information on how I can control an R/C
servo to variably open and close a valve (0-90 degree range). I've got the
servos (so I don't need the driver stuff) and certainly have enough PIC's
laying around here that I should be able to cobble together a prototype. I
just seems that most of the things I'm finding are related to multiple
servos. This idea is much more simple - 1 servo driven from 1 rheostat.

If you know someplace I can look for clues, please send them along. Been to
a bunch of robotic sites too! and no, I don't want an assembled controller.

Thanks for your bandwidth.

-DO

1999\05\20@211034 by tim

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I WANT TO RESPOND ON YOUR SUBJECT OF
servo control for positioning using rheostat if i trade info will u help
me?
with pic programers and use there of?
can u help i know servo positon ways of systems and accuracy??

{Original Message removed}

1999\05\20@222655 by David Olson

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[My message snipped, tim's message included]

> I WANT TO RESPOND ON YOUR SUBJECT OF
> servo control for positioning using rheostat if i trade info will u help
> me?
> with pic programers and use there of?
> can u help i know servo positon ways of systems and accuracy??

This is probably going to swing way off topic....

Well, I'd like to help but, I have a "recent" knowledge of the PIC
environment that spans about 6 months. My domain is the PICStart programmer
and a few of Microchip's proto boards, as well as the prototypes for my
projects. Unfortunately, my mode of operation in the PICList is largely
questions since I don't have a lot of answers yet (although I may have made
a few contributions).

Which brings me to a dilemma. True, I've asked for help. True, there should
be some form of reciprocation however, I'm not in the same league as most of
the PICList members and I am usually very hesitant to post a question. I
always peruse the archives and do a few days of Web searches before I come
to the masters, and even then, I hesitate - largely because these folks
worked hard to get the knowledge they have and I'm in no position to ask for
a handout (should have been an EE and not an ME I guess, and now I've hit
the epitome of atrophy - marketing ;))

Now, yes tim, I can try to help but, there are others out there that are
probably more qualified.

Which brings me to my next point. For those that contribute to the list, I
appreciate the wealth of information that you've contributed and posses.
Through the combination of the PIC-related books, stuff like Tony Nixon's
PicNPoke, the archives, and the constant barrage of daily posts, I've
learned to solve a lot of my problems.

I suppose if someone were looking for marketing help....never mind (although
Microchip may need some).

-DO

1999\05\21@024619 by Jamil J. Weatherbee

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I believe R/C servos work on a 1-2ms pulse system.  i.e. depending on the
length of the supplied pulse 1ms for all the way one direction 2ms for all
the way the other direction etc. There are some beginning PIC books I was
flipping through in Barnes&Noble that had detailed information on this.
Wish I could remember the name.


On Thu, 20 May 1999, David Olson wrote:

{Quote hidden}

1999\05\21@071357 by tim

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i understand where you are coming from and me too.just got started with pic
chips .i have two programmers and didn't even power them up yet........ they
were given to me by a friend ..........and he is too busy   consulting  for
the big microchip and he has his own co also..hehe how nice.....
i build small servo systems and do it all with an analogue voltage balancing
scheme's ......                                         work's very
well........microchip has an application note
using pic to control positioning of a motor using rheostat feedback...but
I'm a little confused as to how the commands are sent to the chip for the
position.......i.e software program
but if i can be of help ........i will help..............tim
{Original Message removed}

1999\05\21@074036 by David Olson

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I've got the PIC'n up the PACE book, which does go into some PWM which has
helped a bit. The other thing is that I'm not looking to do this in
software - especially where the A/D comes in with the POT controlling the
angle of the servo. I'd like to do it without a separate A/D chip (unless
the resolution and reliability is better).

-DO

> {Original Message removed}

1999\05\21@081401 by paulb

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David Olson wrote:

> This idea is much more simple - 1 servo driven from 1 rheostat.

 The simple answer, is to use a standard 7555 (CMOS 555) circuit

 +6V o----+--------+------+
          |     ___|______|___               C  = 15nF
          <    |   8      4   |              R1 = 220k
       R1 <    |              |              R2 = 8k2 in series with
          |    |              |    |\             10k control pot
          +----|7            3|----| o--o Out
          |    |              |    |/
          <    |              |   Inverter
       R2 <    |    7555      |
          |    |              |
          +----|2             |
          +----|6            5|--+
          |    |              |  |
       C ===   |              | === 100nF
          |    |              |  |
          |    |___1__________|  |
          |        |             |
 Gnd o----+--------+-------------+

--
 Cheers,
       Paul B.

1999\05\21@123139 by Andy Kunz

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At 10:11 PM 5/21/99 +1000, you wrote:
>David Olson wrote:
>
>> This idea is much more simple - 1 servo driven from 1 rheostat.
>
>  The simple answer, is to use a standard 7555 (CMOS 555) circuit

More simple - use 1 8-pin PIC and 1 pot.

Andy

==================================================================
  Montana Design Tech Support - http://www.montanadesign.com
==================================================================

1999\05\21@125205 by Adam Bryant

picon face
David,
Here is a small project I sent out a few weeks ago that might be at least
part of what you are looking for.  This simple servo cycler uses a
12C508/9 and a single pushbutton.  When the button is pushed it cycles
the servo to one side, waits 3 seconds, cycles the servo to the other
extreme, waits 3 seconds, then returns the servo to the center.  Instead
of the pushbutton switch you could easily add a rheostat (there is a
Microchip App Note and several web sites that tell how to read a
rheostat), measure the rheostat and convert that to your pulse width to
send to the servo.  I use this simple circuit to help install servos in
R/C airplanes and it should be easily modifiable for what you need.

Adam

On Thu, 20 May 1999 20:53:06 -0400 David Olson <spam_OUTdolsonTakeThisOuTspamPROGRESS.COM>
writes:
> I'm wondering of someone can point me in a PWM direction.
SNIP
> servos. This idea is much more simple - 1 servo driven from 1
> rheostat.
SNIP
> -DO
>

+5v--+------------------------------------------+---------------To Servo
+
    |                                                 |
    |                                                 >
    |                                                 < 10K
    |  +-------+                                      >
    +--|vdd      |                                    |
        |    GP0|-------------------------------+
        |        |                                    |
        |        |                                    0 |
        |        |                                       |-- N.O pushbutton swi
tch
        |    GP1|---To Servo signal line               0 |
    +--|vss      |                                     |
    |  +-------+                                       |
    |                                                  |
Gnd--+------------------------------------------+---------------To Servo
-


;********************************************************************
; SERV_SET.ASM
; Servo setup device utilizing a 12C508/9.
;
; This file will implement a servo setup device utilizing a 12C509.
; To reduce parts count, the internal oscillator will be used.
;
; Operation:
;       A single button will be included for user interaction with
; this device.  A press of the button will cycle the servo all the
; way to the low end, hold for two seconds, cycle the servo all the
; way to the high end, hold for two seconds, then return the servo
; to the center.
;********************************************************************

; Include register equates and what-not

       list p=12C509
       include p12c509.inc

;==== LOCAL DEFINES =============================
#define INPUT           GPIO,0
#define OUTPUT_ON       BSF     GPIO,1
#define OUTPUT_OFF      BCF     GPIO,1

;==== LOCAL MACROS ==============================
PULSE_ON MACRO          OP1
       OUTPUT_ON
       MOVLW           OP1
       MOVWF           width
       CALL            Output
       ENDM

PULSE_OFF MACRO         OP1
       OUTPUT_OFF
       MOVLW           OP1
       MOVWF           width
       CALL            Output
       ENDM

CBLOCK 0x07
       counter
       flag
       width
       dcount
ENDC

       ORG     0
       MOVWF   OSCCAL          ; write preset factory calibration value.

Init
       MOVLW   b'01001000'
       OPTION

       MOVLW   b'11000001'     ;should make bits 1 output, 0 input
       TRIS    GPIO

       CLRF    flag
       CLRF    GPIO

Main
       PULSE_ON        .15
       PULSE_OFF       .185
       MOVF            flag,F  ; test if flag is zero
       SKPNZ
       GOTO            Main

Key_pressed
       MOVLW           .150    ; output 1ms pulse width for 3 seconds.
3 seconds will
       MOVWF           counter ; give it time to cycle to the endpoint
and hold for at least 2 seconds.
Out_1ms
       PULSE_ON        .10
       PULSE_OFF       .190
       DECFSZ          counter,F
       GOTO            Out_1ms

       MOVLW           .150    ; output 2ms pulse width for 3 seconds
       MOVWF           counter
Out_2ms
       PULSE_ON        .20
       PULSE_OFF       .180
       DECFSZ          counter,F
       GOTO            Out_2ms

       CLRF            flag    ; reset the flag register.  Doing it here
will provide a crude form of
                               ; debouncing.
       GOTO            Main

       ; Output routine.
       ; This routine is basically a 100us delay loop with a test for a
button press.
       ; If the button is pressed, the flag register will be set and
tested for elsewhere.
       ; This routine is repeated "width" times
Output

Test_key
       ;this routine implements a 100us timing loop
       ;Delay calculation is as follows:
       ; .000090   - 5 cycle loop 18 times.
       ; .000004   - last time through delay loop
       ; .000006   - delay for this loops setup
       ; .000100   - total
       MOVLW           .19
       MOVWF           dcount
       NOP
       BTFSS           INPUT
       BSF             flag,0
       DECFSZ          dcount,F
       GOTO            $ - 3           ; Go back to button press test

       DECFSZ          width,F
       GOTO            Test_key        ; Do until width = 0

       RETURN

       END





Adam Bryant (age 0x23)
.....abryantKILLspamspam@spam@peaktech.com (work)
adamdbspamKILLspamjuno.com (home)
Parker, CO, USA
Robotics, RC Airplanes, anything using a PIC

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1999\05\21@173807 by ShadeDemon

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 Your lucky timing..  Was just sent this on the SRS list:

                   +-------+----->|----+
                   |      150k         |
                   |       |           |
+5v--220kpot--4.7k--+-->|---+--|HCT14>--+---->servo
                           |
                           = 100n
                           |
                          GND

 I haven't tested this yet of course, but should be
interesting!  And 6 per hct14.  If you need a clearer sch I
could send the gif..
Alan

David Olson wrote:
> servos. This idea is much more simple - 1 servo driven from 1 rheostat.
>
> If you know someplace I can look for clues, please send them along. Been to
> a bunch of robotic sites too! and no, I don't want an assembled controller.
>
> Thanks for your bandwidth.
>
> -DO

1999\05\21@180121 by Mo

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face
> Anyway, I'm looking for information on how I can control an R/C
> servo to variably open and close a valve (0-90 degree range
> This idea is much more simple - 1 servo driven from 1 rheostat.
David
Even simpler, take the knob off the rheostat, stick the knob straight onto
the valve and go for direct drive!

Mo

1999\05\21@182825 by tim

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e-mail me at        STM 800@ city-net.com
----- Original Message -----
From: Mo <.....moKILLspamspam.....MAGNUM.NDIRECT.CO.UK>
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Friday, May 21, 1999 9:58 PM
Subject: Re: [OT] PWM Servo Directions


> > Anyway, I'm looking for information on how I can control an R/C
> > servo to variably open and close a valve (0-90 degree range
> > This idea is much more simple - 1 servo driven from 1 rheostat.
> David
> Even simpler, take the knob off the rheostat, stick the knob straight onto
> the valve and go for direct drive!
>
> Mo
>

1999\05\21@190611 by William Chops Westfield

face picon face
   More simple - use 1 8-pin PIC and 1 pot.

Does this require an A/D PIC, or can you do RC based A/D conversion in
SW on something like a 12C508 using inherent pin capacitance for the C?

Thanks
BillW

1999\05\21@191024 by Andy Kunz

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At 04:04 PM 5/21/99 -0700, you wrote:
>    More simple - use 1 8-pin PIC and 1 pot.
>
>Does this require an A/D PIC, or can you do RC based A/D conversion in
>SW on something like a 12C508 using inherent pin capacitance for the C?

Either one for me, but I've talked with him directly and he really needs an
ADC.

Andy
==================================================================
  Montana Design Tech Support - http://www.montanadesign.com
==================================================================

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