> I've got a variable frequency signal (200hz to 4khz) whose frequency I
want
> to increase by 30% (5v signal).  IE if the input frequency is 1000hz, I
> want to output 1300hz.  Is there an easy method of doing this?  I've heard
> of PLL, but don't have a clue how to build them, so if there's an easier
> option that would be great.
>
> Gary



It depends on what you need to do with the signal.

If the resulting output signal can have significant jitter, and unequal size
cycles then this job can easily be done with a single component: an 8-pin
PIC. If you need to keep a 'square wave' output then it gets a little
trickier, but can still be done in a small PIC.

Just to give you an idea of how you could do it if jitter and output cycle
size don't matter:

; =====================
; The main loop. Each iteration of this loop processes ten
; cycles of the input signal (in the copypulse routine). Three of
; those cycles are doubled by calling the outpulse routine
; to send an extra pulse in the low portion of the input
; pulse.

mainloop:
    call    copypulse
    call    copypulse
    call    copypulse
    call    outpulse
    call    copypulse
    call    copypulse
    call    copypulse
    call    outpulse
    call    copypulse
    call    copypulse
    call    copypulse
    call    outpulse
    call    copypulse
    goto    mainloop

; ===== copy an input pulse to the output pin ======

copypulse:

; look for the rising edge

waithi:
    btfss    INPUT
    goto    waithi
    btfss    INPUT
    goto    waithi

; we just saw a rising edge, copy it to the output

    bsf    OUTPUT

; wait for the input to go low again

waitlo:
    btfsc   INPUT        ; wait for input to be low
    goto    waitlo
    btfsc    INPUT       ; check twice to protect against glitches
    goto    waitlo

; we just saw a falling edge, copy it to the output

    bcf    OUTPUT
    retlw 0

; ===== output an extra pulse =====
;
; At 4Hz (the maximum input frequency) the low level during
; which we have to output our extra pulse lasts for 1/8000
; of a second. We have to fit a low-high-low into that time
; to fit our pulse in. To allow for input jitter and modest
; overfrequency we'll set the time for the first low and high
; to about 1/32000 of a second

outpulse:
; output low for 1/32000 of a second
    call    delay            ; delay 1/32000
; output high for the next 1/32000
    bsf    OUTPUT
    call    delay
; output low until the next pulse
    bcf    OUTPUT
    retlw    0

Bob Ammerman
RAm Systems

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