Doubling the pusle count

[malc-c]

o.k. ONCE again

which car model, brand, year?

Probably not going to mean much to you.

Make and Model: Vauxhall Corsa
Year: ? no idea - will ask him.

All I had to go on was:

My wife Jenny has a Vauxhall Corsa that had just a cable driven speedo. I've gotten hold of an insrtumanet cluster that has tacho and speedo, but the speedo isn't cable, it's electrical. The tach works fine, but the rotary encoder I've picked up (which is supposed to be the right one) is giving only half the number of pulses required by the speedo, i.e. the speedo is reading half the actual speed.
The question I have is....."Is there a simple way to double the number of pulses to the speedo...like a frequency doubling circuit" ??

I believe the unit I have works optically...disc with 10 light dark changes per rev. The easy answer would be to put a disc in the unit with twice the number of segments, but it's not able to be disassembled easily.

[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>