The odometer problem

[100SRV]

I had to replace the speedometer on my "sanity project" vehicle because the odometer / trip meter on the VDO speedometer had become very intermittent. This is apparantly a common problem with this poart. I bought a replacement "Racetech" part which had the bonus of being able to set the odometer to a specific value.

Ideal: I added the mileage from the VDO speedometer to the mileage from the mechanical one which the VDO replaced to get the "current" reading.

BUT

I made a mistake and discovered after setting the value (a one-time only feature) that I shold have deducted about 45000 miles because I didn't zero the mechanical speedometer when I'd rebuilt the donor into the "sanity project".

Here is the challenge:
The speedometer manufacturer can reset the odometer to a specified value for a fee, I think this is in the region of £80 + carriage. They "break" it open and reprogram it.

I could do it myself by any of the following methods but the objective is to do it (relatively simply) and cheaper than the cost of sending it back.

So far I have, in decreasing order of Heath-Robinsonness:
Build a rig with a spare sensor, power up the speedometer and use a motor- revolve a wheel with suitable targets until I get the value I need.
Use a square wave generator to do similar to the above
Both those options will need the speedometer to be monitored so aren't ideal an open to mistakes.

Alternatively I could use something like a Siemens Logo with a predetermined counter to drive an output to get the value I want "automatically" but I've deleted all the old programming code for this I used to have and a starter kit is around £300 so thats out of my target cost.

What other cost-effective things could I use?
Is there an I/O board I could use with a PC where the PC runs a program in a similar manner to a PLC?

Open to suggestions!

[wibble cb]

Jack it up and put it reverse

[eliot]

Arduino with a counter loop to the desired value?

[Mercdriver]

Are you from Car clockers R us?

[100SRV]

eliot said:

Arduino with a counter loop to the desired value?

Good shout, know nothing about them - is this sort of thing suitable?
"Arduino K000007 Starter Kit Including Uno Board"

[eliot]

You need to understand what type of signal the odo is expecting - Arduino will only drive 5v signal, so may need a transistor if it expects 12v.

the code is simple, chatgpt will write something for you or I can help - I’m not far from you.

I don’t quite understand why you want to increase the mileage when you said you needed to remove 45k miles from it though

[100SRV]

eliot said:

You need to understand what type of signal the odo is expecting - Arduino will only drive 5v signal, so may need a transistor if it expects 12v.

the code is simple, chatgpt will write something for you or I can help - I’m not far from you.

I don’t quite understand why you want to increase the mileage when you said you needed to remove 45k miles from it though

Odometer only increments so I'd need to count to roll over back to zero plus the actual mileage the vehicle has done.

[100SRV]

Doing some rough sums I'm not sure whether the speedometer could be clocked fast enough to do this job in reasonable time. I make the target count as follows:
1,000,000-145,000=855,000 which gets the odometer to read all zeroes
Target is about 97,000 so I'd need to add 952,000 miles which at a steady 150mph is 6346ish hours or 264 days...

Or is my maths wrong?