Doubling the pusle count

[mister_e]

Maybe you didn't know it alrady but, i've been a car accessoiries installer (alarm, car starter, radio, gps, etc etc ) for over 12 years and i still do some custom car modification here and there.

Why i asked, is because most cruise control brand have their own application list and hints. Even on some VSS generated cable, some cars may have another source for an optional Cruise control or else. And you was right... i never see any opel/vauxhall here... only few picture here and there over the web.

Anyways, without knowing the exact frequency range, Darrel's example have to work within it's range... no doubt on it!

To interface.. a simple NPN or PNP or simple OP-AMP would do the job pretty well. I don't think 12V amplitude is really needed... maybe 5Volts could work... with a simple resistor in serie.

Hey.. you didn't SIMed it this time ?

[malc-c]

Steve, no I didn't know you had the automotive electrical experience.

I'm off to download some spice application and SIM this... or should I just contact a local PCB house and get them to send me a prototype... afterall if its wrong I'll bin that one and order another

Any chance of a quick schematic on the input.. I was planning on using a small 100mA 5v reg for the PICs supply, and assume that the transistor would be between +5 and gnd (C and E) with the base connected to the sensor ?

[mister_e]

What i suspect to work... is something as simple as...
<img SRC="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1433&stc=1&d=117279195 7">

for the input, a simple resistor in serie will work without problem (1-10k), OR a simple voltage divider.

[Darrel Taylor]

The pulses appear to be 0-12-0 "square" wave, but not 50/50 duty cycle.

I was hoping it would be the easy way (50%).
Oh well, back to the drawing board. I'm re-writing it now.

Should have something later today (that's probably tomorrow for your time period).
<br>

[mister_e]

Darrel... i don't think it will be revealant to be 50% or not... it's all about pulse/miles after all.

In the good ol' time we installed 2 magnetic sensor on the drive shaft as a VSS generator. using that... no way you could have a 50% duty cycle as the magnets where about 1 inch wide.

I should take a car ride here and record the VSS signal to see how clean it is... in case some want to know.

[mister_e]

AAAAAAAAAAAHAHAHAHAHAHHA i knew that one of my OLD cruise control installation manual would be handy one day or another... here's a quote of the revealant part...
<table><tr><td></td><td>

Using a multimeter to measure the frequency
of the VSS pulse. Usually, the PPM
(pulses per mile) of the VSS signal is
known. At 40 km/hr (25 mph) the following
frequencies should be:
2000 PPM : 14 hz
4000 PPM : 28 hz
5000 PPM : 35 hz
8000 PPM : 56 hz

</td><td></td></tr></table>

[Darrel Taylor]

It was easier than I thought, just more of the same stuff.

<table><tr><td>

IdleState CON 0

</td><td>

IdleState CON 1

</td></tr></table>

'****************************************************************
'*  Name    : FREQx2.bas                                        *
'*  Author  : Darrel Taylor                                     *
'*  Date    : 3/1/2007                                          *
'*  Version : 2.0                                               *
'*  Notes   : Doubles the frequency of input pulses,            *
'*          : and maintains the same DutyCycle as the Input.    *
'*          : Range = .1hz to 500 hz  (0-40% DutyCyle)          *
'*          : Target = PIC12F629/675                            *
'****************************************************************
@  __config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_OFF & _CP_OFF
DEFINE  NO_CLRWDT 1

Clear

SpeedPin   VAR GPIO.2                       ; Input from speed sensor
SpeedX2Pin VAR GPIO.4                       ; Output to Speedometer
IdleState  CON 0                            ; State of input when sensor
                                            ;    is not on a "Slot"
NotIdle    CON IdleState ^ 1
LastState  VAR BIT                          ; Last state the Input changed to
LoopCount  VAR byte                         ; Counts the loops of each pulse
LoopCount1 VAR byte
LoopCount2 VAR byte

PulseWidth  VAR byte  BANK0                 ; Counts the loops of output pulse
PulseWidth1 VAR byte  BANK0
PulseWidth2 VAR byte  BANK0

LastPulseWidth  VAR byte                    ; saved width of last pulse
LastPulseWidth1 VAR byte                    ;    so it can duplicate it
LastPulseWidth2 VAR byte

CycleWidth  VAR byte  BANK0                 ; Counts the loops of output cycle
CycleWidth1 VAR byte  BANK0
CycleWidth2 VAR byte  BANK0

OutPulseCount VAR BIT


CMCON = 7
'ANSEL = 0    ; for 12F675

SpeedX2Pin = IdleState
OUTPUT SpeedX2Pin

Main:
    LoopCount = LoopCount + 1               ; 24-bit counter
    If LoopCount = 0 Then
        LoopCount1 = LoopCount1 + 1         
        if LoopCount1 = 0 then
            LoopCount2 = LoopCount2 + 1
        endif
    endif
    IF SpeedPin <> LastState then           ; If Input State Changed?
        LastState = SpeedPin
        
        if LastState = NotIdle then         ; Start of Input Pulse
            CycleWidth  = LoopCount
            CycleWidth1 = LoopCount1
            CycleWidth2 = LoopCount2
            ASM
                bcf   STATUS,C              ; CycleWidth = LoopCount / 2
                rrf   _CycleWidth2, F       ; Output Cycle is half of Input
                rrf   _CycleWidth1, F
                rrf   _CycleWidth, F
            ENDASM
            LoopCount  = 0                  ; reset LoopCount
            LoopCount1 = 0
            LoopCount2 = 0
        else                                ; End of Input Pulse
            PulseWidth  = LoopCount
            PulseWidth1 = LoopCount1
            PulseWidth2 = LoopCount2
            ASM
                bcf   STATUS,C              ; PulseWidth = PulseWidth / 2
                rrf   _PulseWidth2, F       ; Output Pulse is half of Input
                rrf   _PulseWidth1, F
                rrf   _PulseWidth, F
            ENDASM
            LastPulseWidth = PulseWidth
            LastPulseWidth1 = PulseWidth1
            LastPulseWidth2 = PulseWidth2
            SpeedX2Pin = NotIdle            ; start First Output Pulse
            OutPulseCount = 0
        endif
    else
        if SpeedX2Pin = NotIdle then
            if PulseWidth = 0 then          ; countdown output time (24bit)
                if PulseWidth1 = 0 then
                    if PulseWidth2 = 0 then
                        SpeedX2Pin = IdleState ; end of pulse, 
                    else                       ; wait for next transition
                        PulseWidth2 = PulseWidth2 - 1
                        PulseWidth1 = 255
                        PulseWidth  = 255
                    endif
                else
                    PulseWidth1 = PulseWidth1 - 1
                    PulseWidth  = 255
                endif
            else
                PulseWidth = PulseWidth - 1
            endif
        else
          @ NOP                             ; Keep the loop symmetrical
          @ NOP
          @ NOP
          @ NOP
          @ NOP
        endif
        
        if OutPulseCount = 0 then
            if CycleWidth = 0 then          ; countdown to Midpoint of cycle
                if CycleWidth1 = 0 then
                    if CycleWidth2 = 0 then
                        SpeedX2Pin = NotIdle ; Start second pulse
                        OutPulseCount = 1
                        PulseWidth  = LastPulseWidth
                        PulseWidth1 = LastPulseWidth1
                        PulseWidth2 = LastPulseWidth2
                    else
                        CycleWidth2 = CycleWidth2 - 1
                        CycleWidth1 = 255
                        CycleWidth  = 255
                    endif
                else
                    CycleWidth1 = CycleWidth1 - 1
                    CycleWidth  = 255
                endif
            else
                CycleWidth = CycleWidth - 1
            endif
        else
          @ NOP                             ; Keep the loop symmetrical
          @ NOP
          @ NOP
          @ NOP
        endif
    endif
goto Main
end

HTH,