>
> From: Joel Middleton <chopsuey1973KILLspamYAHOO.COM>
> Date: 2003/06/15 Sun AM 01:21:50 EDT
> To: .....PICLISTKILLspam.....MITVMA.MIT.EDU
> Subject: [PIC]: Servo Pulse Problem
>
> I believe I am having a problem with the pulse I am
> sending to a servo connected directly to portb pin 3.
> I have tmr0 set to overflow ever .0001 seconds. The
> variable 'count' is incremented each time tmr0
> overflows when count reaches 200 it is reset to 0.
> When count is equal to zero I set portb pin 3 and when
> count equals pw1 I clear the pin. I believe this
> should give me a 1ms pulse every 20ms. This was not
> working like I thought and I wanted to take a look at
> the pulse so I downloaded one of those ocilloscopes
> that runs through a sound card as I did not have
> access to a real one. Well I found out that I am not
> getting a nice square wave. The rising edge looks fine
> but the falling edge is a slope. Can anyone tell me
> how to correct this? I have included my code and also
> attached an image I captured from the occiloscope.
> Thanks.
>
>
> LIST R=DEC
>
> INCLUDE "p16f84a.inc"
>
> CBLOCK 0x0C
> _w
> _status
> _pclath
> _fsr
> count
> pw1
> ENDC
>
> __CONFIG _CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON
>
> push    macro
>         movwf   _w                      ;Save registers
>         movf    STATUS, w
>         movwf   _status
>         movf    PCLATH, w
>         movwf   _pclath
>         clrf    PCLATH
>         endm
>
> pull    macro
>         swapf   _pclath, w
>         movwf   PCLATH
>         movf    _status, w      ;Restore registers
>         movwf   STATUS
>         swapf   _w, f
>         swapf   _w, w
>         endm
>
> PAGE
>
>         org             0
>         nop
>
>         goto    Main
>
>         org             4                       ;Interrupt
>
>         push
>
> Timer0
>         btfss   INTCON, T0IF
>                 goto    Iend
>         movlw   165
>         movwf   TMR0
>         bcf             INTCON, T0IF
>         incf    count
>         movlw   200
>         subwf   count, W
>         btfss   STATUS, Z
>                 goto    Step1
>         movlw   0
>         movwf   count
> Step1
>         movlw   0
>         subwf   count, 0
>         btfsc   STATUS, Z
>                 bsf             PORTB, 3
>         movf    pw1, W
>         subwf   count, 0
>         btfsc   STATUS, Z
>                 bcf             PORTB, 3
> Iend
>
>         pull
>
>         retfie
>
> Main
>
>         bsf             INTCON, GIE
>         bsf             INTCON, T0IE
>
>         bsf     STATUS, RP0
>         bcf             OPTION_REG, T0CS
>         bsf             OPTION_REG, PSA
>     bcf         STATUS,RP0          ; RAM PAGE 0
>
>         movlw   156
>         movwf   TMR0
>
>         clrf    PORTB
>
>         bsf     STATUS, RP0
>         bcf     TRISA ^ 0x080, 1
>         bcf     TRISA ^ 0x080, 2
>         clrf    TRISB
>         bcf     STATUS, RP0
>
>         clrf    PORTA
>         clrf    PORTB
>         clrf    count
>
>         movlw   10
>         movwf   pw1
>
> Loop
>         nop
> goto    Loop
> end
>
>
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>
>
>

> > Well I found out that I am not
> > getting a nice square wave. The rising edge looks
> fine
> > but the falling edge is a slope.
>
> This depends on the external circuit.  Something
> must be sourcing lots of
> current (almost certainly above spec) when the PIC
> tries to lower the pin,
> or the low side driver is blown.  Did you forget a
> flyback diode?
>
> If the timing is otherwise right, then it's not a
> software problem.
>
> <undocumented absolute mode code ignored and
> snipped>
>
>
>

>Yes I do not have a flyback diode. I am not sure how
>to implement this with a servo, are they any examples
>on the web that I can look at?
>
>--- Olin Lathrop <spamBeGoneolin_piclistspamBeGoneEMBEDINC.COM> wrote:
> > > Well I found out that I am not
> > > getting a nice square wave. The rising edge looks
> > fine
> > > but the falling edge is a slope.
> >
> > This depends on the external circuit.  Something
> > must be sourcing lots of
> > current (almost certainly above spec) when the PIC
> > tries to lower the pin,
> > or the low side driver is blown.  Did you forget a
> > flyback diode?
> >
> > If the timing is otherwise right, then it's not a
> > software problem.
> >
> > <undocumented absolute mode code ignored and
> > snipped>
> >
> >
> >
>*****************************************************************
> > Embed Inc, embedded system specialists in Littleton
> > Massachusetts
> > (978) 742-9014, http://www.embedinc.com
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu
>
>
>__________________________________
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>SBC Yahoo! DSL - Now only $29.95 per month!
>http://sbc.yahoo.com
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> I'm certainly no expert, but it looks like a classic
> capacitor discharge issue to me.  If you have a cap
> on this output, it will take time for it to
> discharge causing the slow decay in voltage instead
> of a nice sharp corner.  I can't see your circuit
> but do you have a cap connected across the pin you
> measured with the scope?
> >
> > From: Joel Middleton <RemoveMEchopsuey1973EraseMEEraseMEYAHOO.COM>
> > Date: 2003/06/15 Sun AM 01:21:50 EDT
> > To: RemoveMEPICLISTspam_OUTKILLspamMITVMA.MIT.EDU
> > Subject: [PIC]: Servo Pulse Problem
> >
> > I believe I am having a problem with the pulse I
> am
> > sending to a servo connected directly to portb pin
> 3.
> > I have tmr0 set to overflow ever .0001 seconds.
> The
> > variable 'count' is incremented each time tmr0
> > overflows when count reaches 200 it is reset to 0.
> > When count is equal to zero I set portb pin 3 and
> when
> > count equals pw1 I clear the pin. I believe this
> > should give me a 1ms pulse every 20ms. This was
> not
> > working like I thought and I wanted to take a look
> at
> > the pulse so I downloaded one of those
> ocilloscopes
> > that runs through a sound card as I did not have
> > access to a real one. Well I found out that I am
> not
> > getting a nice square wave. The rising edge looks
> fine
> > but the falling edge is a slope. Can anyone tell
> me
> > how to correct this? I have included my code and
> also
> > attached an image I captured from the occiloscope.
> > Thanks.
> >
> >
> > LIST R=DEC
> >
> > INCLUDE "p16f84a.inc"
> >
> > CBLOCK 0x0C
> > _w
> > _status
> > _pclath
> > _fsr
> > count
> > pw1
> > ENDC
> >
> > __CONFIG _CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON
> >
> > push    macro
> >         movwf   _w                      ;Save
> registers
> >         movf    STATUS, w
> >         movwf   _status
> >         movf    PCLATH, w
> >         movwf   _pclath
> >         clrf    PCLATH
> >         endm
> >
> > pull    macro
> >         swapf   _pclath, w
> >         movwf   PCLATH
> >         movf    _status, w      ;Restore registers
> >         movwf   STATUS
> >         swapf   _w, f
> >         swapf   _w, w
> >         endm
> >
> > PAGE
> >
> >         org             0
> >         nop
> >
> >         goto    Main
> >
> >         org             4
> ;Interrupt
> >
> >         push
> >
> > Timer0
> >         btfss   INTCON, T0IF
> >                 goto    Iend
> >         movlw   165
> >         movwf   TMR0
> >         bcf             INTCON, T0IF
> >         incf    count
> >         movlw   200
> >         subwf   count, W
> >         btfss   STATUS, Z
> >                 goto    Step1
> >         movlw   0
> >         movwf   count
> > Step1
> >         movlw   0
> >         subwf   count, 0
> >         btfsc   STATUS, Z
> >                 bsf             PORTB, 3
> >         movf    pw1, W
> >         subwf   count, 0
> >         btfsc   STATUS, Z
> >                 bcf             PORTB, 3
> > Iend
> >
> >         pull
> >
> >         retfie
> >
> > Main
> >
> >         bsf             INTCON, GIE
> >         bsf             INTCON, T0IE
> >
> >         bsf     STATUS, RP0
> >         bcf             OPTION_REG, T0CS
> >         bsf             OPTION_REG, PSA
> >     bcf         STATUS,RP0          ; RAM PAGE 0
> >
> >         movlw   156
> >         movwf   TMR0
> >
> >         clrf    PORTB
> >
> >         bsf     STATUS, RP0
> >         bcf     TRISA ^ 0x080, 1
> >         bcf     TRISA ^ 0x080, 2
> >         clrf    TRISB
> >         bcf     STATUS, RP0
> >
> >         clrf    PORTA
> >         clrf    PORTB
> >         clrf    count
> >
> >         movlw   10
> >         movwf   pw1
> >
> > Loop
> >         nop
> > goto    Loop
> > end
> >
> >
> > __________________________________
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> >
> >
>
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>
>
>

> ATTACHMENT part 2 image/pjpeg name=pulse.jpg

> At 10:12 AM 6/15/2003 -0700, Joel Middleton wrote:
>
> >I found this schematic on the web and this is my
> exact
> >circuit except the servo signal is connected to pin
> 3
> >on portb. Also I have all the unused pins connected
> to
> >ground. Anyone see anything wrong with the circuit?
>
> A couple potential problems. (pun)
>
> Running a servo motor from your logic supply is a
> bad idea.
> The motor has relatively large stall current
> demands, and produces a lot of noise. These both
> have the potential to reset or crash the micro.
>
> Try providing a separate supply for the servo motor,
> like four AA cells.
> Keep the ground tied between the supplies though as
> that provides the reference for the pulse.
>
> Also, I've found that I need a series resistor of
> 100 ohms to 1k between the micro and the servo's
> pulse input. I've never investigated why, but I've
> had a few chips blown (Atmel AVRs) when I didn't
> have that series resistor.
>
> It's never a real good idea to take uP I/O pins
> directly into the real world.
>
> --
> http://www.piclist.com hint: To leave the PICList
> .....piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

> I'm certainly no expert, but it looks like a classic capacitor discharge
> issue to me.  If you have a cap on this output, it will take time for it to
> discharge causing the slow decay in voltage instead of a nice sharp corner.
>  I can't see your circuit but do you have a cap connected across the pin
> you measured with the scope?
>
> > From: Joel Middleton <.....chopsuey1973RemoveMEYAHOO.COM>
> > Date: 2003/06/15 Sun AM 01:21:50 EDT
> > To: RemoveMEPICLISTspamBeGoneMITVMA.MIT.EDU
> > Subject: [PIC]: Servo Pulse Problem
> >
> > I believe I am having a problem with the pulse I am
> > sending to a servo connected directly to portb pin 3.
> > I have tmr0 set to overflow ever .0001 seconds. The
> > variable 'count' is incremented each time tmr0
> > overflows when count reaches 200 it is reset to 0.
> > When count is equal to zero I set portb pin 3 and when
> > count equals pw1 I clear the pin. I believe this
> > should give me a 1ms pulse every 20ms. This was not
> > working like I thought and I wanted to take a look at
> > the pulse so I downloaded one of those ocilloscopes
> > that runs through a sound card as I did not have
> > access to a real one. Well I found out that I am not
> > getting a nice square wave. The rising edge looks fine
> > but the falling edge is a slope. Can anyone tell me
> > how to correct this? I have included my code and also
> > attached an image I captured from the occiloscope.
> > Thanks.
> >
> >
> > LIST R=DEC
> >
> > INCLUDE "p16f84a.inc"
> >
> > CBLOCK 0x0C
> > _w
> > _status
> > _pclath
> > _fsr
> > count
> > pw1
> > ENDC
> >
> > __CONFIG _CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON
> >
> > push    macro
> >         movwf   _w                      ;Save registers
> >         movf    STATUS, w
> >         movwf   _status
> >         movf    PCLATH, w
> >         movwf   _pclath
> >         clrf    PCLATH
> >         endm
> >
> > pull    macro
> >         swapf   _pclath, w
> >         movwf   PCLATH
> >         movf    _status, w      ;Restore registers
> >         movwf   STATUS
> >         swapf   _w, f
> >         swapf   _w, w
> >         endm
> >
> > PAGE
> >
> >         org             0
> >         nop
> >
> >         goto    Main
> >
> >         org             4                       ;Interrupt
> >
> >         push
> >
> > Timer0
> >         btfss   INTCON, T0IF
> >                 goto    Iend
> >         movlw   165
> >         movwf   TMR0
> >         bcf             INTCON, T0IF
> >         incf    count
> >         movlw   200
> >         subwf   count, W
> >         btfss   STATUS, Z
> >                 goto    Step1
> >         movlw   0
> >         movwf   count
> > Step1
> >         movlw   0
> >         subwf   count, 0
> >         btfsc   STATUS, Z
> >                 bsf             PORTB, 3
> >         movf    pw1, W
> >         subwf   count, 0
> >         btfsc   STATUS, Z
> >                 bcf             PORTB, 3
> > Iend
> >
> >         pull
> >
> >         retfie
> >
> > Main
> >
> >         bsf             INTCON, GIE
> >         bsf             INTCON, T0IE
> >
> >         bsf     STATUS, RP0
> >         bcf             OPTION_REG, T0CS
> >         bsf             OPTION_REG, PSA
> >     bcf         STATUS,RP0          ; RAM PAGE 0
> >
> >         movlw   156
> >         movwf   TMR0
> >
> >         clrf    PORTB
> >
> >         bsf     STATUS, RP0
> >         bcf     TRISA ^ 0x080, 1
> >         bcf     TRISA ^ 0x080, 2
> >         clrf    TRISB
> >         bcf     STATUS, RP0
> >
> >         clrf    PORTA
> >         clrf    PORTB
> >         clrf    count
> >
> >         movlw   10
> >         movwf   pw1
> >
> > Loop
> >         nop
> > goto    Loop
> > end
> >
> >
> > __________________________________
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> > SBC Yahoo! DSL - Now only $29.95 per month!
> > http://sbc.yahoo.com
> >
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> > spamBeGonepiclist-unsubscribe-request@spam@spam_OUTmitvma.mit.edu

> Yes I do not have a flyback diode. I am not sure how
> to implement this with a servo, are they any examples
> on the web that I can look at?
>
> --- Olin Lathrop <olin_piclistEraseMEEMBEDINC.COM> wrote:
> > > Well I found out that I am not
> > > getting a nice square wave. The rising edge looks
> >
> > fine
> >
> > > but the falling edge is a slope.
> >
> > This depends on the external circuit.  Something
> > must be sourcing lots of
> > current (almost certainly above spec) when the PIC
> > tries to lower the pin,
> > or the low side driver is blown.  Did you forget a
> > flyback diode?
> >
> > If the timing is otherwise right, then it's not a
> > software problem.
> >
> > <undocumented absolute mode code ignored and
> > snipped>
>
> *****************************************************************
>
> > Embed Inc, embedded system specialists in Littleton
> > Massachusetts
> > (978) 742-9014, http://www.embedinc.com
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > RemoveMEpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu
>
> __________________________________
> Do you Yahoo!?
> SBC Yahoo! DSL - Now only $29.95 per month!
> http://sbc.yahoo.com

> I just duplicated your set up with a 16F628, Futaba
> 9101 servo and 4 AA
> batteries as a power supply.
> The wave form was nice and square on a Tektronix
> 475A scope.
>
> The servo locked up nice & tight indicating all is
> working...
>
> Be certain that
>    Black is ground
>    Red is Vcc (center lead)
>    White is signal
>
> John Ferrell
> 6241 Phillippi Rd
> Julian NC 27283
> Phone: (336)685-9606
> johnferrellspamBeGoneearthlink.net
> Dixie Competition Products
> NSRCA 479 AMA 4190  W8CCW
> "My Competition is Not My Enemy"
>