Post by thread:[OT] PWM Servo Directions

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

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}

[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

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}> 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 >

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}

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}

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.

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 ==================================================================

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_OUTdolsonTakeThisOuTPROGRESS.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) .....abryantKILLspam@spam@peaktech.com (work) adamdbKILLspamjuno.com (home) Parker, CO, USA Robotics, RC Airplanes, anything using a PIC ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]

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

> 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

e-mail me at STM 800@ city-net.com ----- Original Message ----- From: Mo <.....moKILLspam.....MAGNUM.NDIRECT.CO.UK> To: <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.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 >

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

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 ==================================================================