Speed pulse convertor

Projects General Guidance
1

Hi everyone.

I have fitted a 1998 bentley engine into a 1960 bentley and i want to keep all the instruments as orginal.

The problem i have is that the speed output of the gearbox computer is a much faster square wave than what the original speedo needs so when the gearbox is doing 30mph the speedo is reading 110mph.

I was wondering how i could use a arduino to read the speed pulse coming from the gearbox and convert it into a slower pulse that the orginal speedo will work with.

Thank you

2

Hi, Great project..

Two levels of issues:

  • What is the voltage level and pulse width of the signal from the gearbox?
  • What is the NEEDED voltage level and pulse width for the Speedo?

Probably the answer is "The Same" ??

So you need three things;

  • Condition the signal from the gearbox for Arduino
  • Create an acceptable Arduino output signal for the Speedo
  • Write a little code that counts input pulse and decides on output pulses.

Do you have access to an oscilloscope to look at the existing signsla? Documentation that discusses it.

We only get our hands on Bentleys this side of the pond if we are Valet Parkers :slight_smile:

3

You can probably use [u]pulseIn()[/u] to read the speed, [u]map()[/u] to scale the frequency, and if it's in the right range [u]tone()[/u] could generate the new-slower pulses.

The advantage of tone() is that it runs continuously in the background so it simplifies the timing.

4

I think the output of the gearbox is 5v signal.

The signal for the speedo is 12v so i know i will need so circuit to change 5v of arduino to 12v.

I do have an oscilloscope so i can measure the signal and post my results.

5

I've worked on '30s Rollers and Bentleys- and wonderful things they are ...

especially....

NO ELECTRONICS!!

regards

Allan

6

Ive also worked on 30s bentleys and yes the electronics in them is basic but after working on bentleys from the 1920s up to modern day electronics makes them alot more fun