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'Help?'
1999\10\13@011456 by Daniel Nagy

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Ok, i got a question for you all. i've been working around PIC micro's for a little time now, done a Engine immobiliser / Central locking based around a 16F84 with a RF receiver.

Anyways, i'm working on a new little project. Its called a "Electronic Ratio Box" basically its used on Electronic Speedo's within Automobiles.
a simple description on why i require it..

I've got a modified car, where as i've changed the Diff Ratio gears, and for those who have done this, you will notice your speedo is now also incorrect.. also in cases when you change the size of your Wheels. in my case. both. for those who are interested, original Diff gears were 2.77:1, now i'm running 3.45:1 (but i've also got 4.11, 3.25 gears). anyways.. the principle is simple.

the Speedo Sender is a Hall Effect sensor, which is a square wave output, varied depending on the speed.
i need this little circuit too interface between the Sender, and the speedo itself.

Also, i want to work with a PIC12C672, as it has a A/D conversion, where i want to connect a trimpot upto (for adjustability, so i can adjust it depending on tyre size, diff gears. ie 80% faster, or slower)

just say the sender is sending 100 pulses
i require this to send out <so many pulses> in the same time span. i believe you all understand what i mean


the problem is, i'm still fairly new to ASM, and i have no idea how i can do this.. any suggestions?

Sent by YAP P/L at http://www.yap.com.au/

1999\10\13@012654 by Nick Taylor

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Daniel,

Sorry, but I can't help you with your speedo project ... but if
you would limit your text line to 72 characters or less, more
people would read your posts.

Good luck,
- Nick -

Daniel Nagy wrote:
>
> Ok, i got a question for you all. i've been working around PIC micro's for a l
ittle time now, done a Engine immobiliser / Central locking based around a 16F84
with a RF receiver.
>
> Anyways, i'm working on a new little project. Its called a "Electronic Ratio B
ox" basically its used on Electronic Speedo's within Automobiles.
> a simple description on why i require it..
>
> I've got a modified car, where as i've changed the Diff Ratio gears, and for t
hose who have done this, you will notice your speedo is now also incorrect.. als
o in cases when you change the size of your Wheels. in my case. both. for those
who are interested, original Diff gears were 2.77:1, now i'm running 3.45:1 (but
i've also got 4.11, 3.25 gears). anyways.. the principle is simple.
>
> the Speedo Sender is a Hall Effect sensor, which is a square wave output, vari
ed depending on the speed.
> i need this little circuit too interface between the Sender, and the speedo it
self.
>
> Also, i want to work with a PIC12C672, as it has a A/D conversion, where i wan
t to connect a trimpot upto (for adjustability, so i can adjust it depending on
tyre size, diff gears. ie 80% faster, or slower)
>
> just say the sender is sending 100 pulses
> i require this to send out <so many pulses> in the same time span. i believe y
ou all understand what i mean
>
> the problem is, i'm still fairly new to ASM, and i have no idea how i can do t
his.. any suggestions?
>
> Sent by YAP P/L at http://www.yap.com.au/

1999\10\13@020043 by Anne Ogborn

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>just say the sender is sending 100 pulses
>i require this to send out <so many pulses> in the same time span. i
believe you all understand what i mean


inherently, any solution is going to have some jitter in it, or have some
lag,
but you just want to change the instantaneous average rate.

what you need is a reverted loop

   n = (256 * number pulses needed) / (per number in)
   accum = 0
   npulse = n / 256;
   n = n % 256;

   for(;;)
   {
       waitforinputpulse();
       for (i = 0 ; i < npulse ; i++)
           output pulse;
       accum += n;
       if (accum >= 256)
       {
           accum -= 256;
           output pulse;
       }
   }

You may be able to eliminate the for(i=... loop and only
test the 0 and 1 conditions if your ratio never exceeds 2.

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