TVR being the engineering geniuses that they were fitted a battery to the odometer in my car... Which means once the battery goes flat the car forgets its mileage. Seemingly the battery was last replaced in 2005 so it's not done too badly!

To rectify this you have to dislocate all upper body joints to unbolt the top of the dashboard, remove the speedo/odometer unit, pry it apart and swap the lithium cell....

That I have managed...what I now need to do is wind the odometer forward....

Firstly the back of the unit has three wires. I guess +ve, Gnd and signal

What format is the signal likely to be? 12v pulse? 5v pulse? Short to ground?


I am going to try and build a pulse generator to wind the tacho forward.....although even at 180 miles an hour its going to take 300 hours....

Pretty high tech for a 20 year old car!!


Any folk have any cunning ideas?!







[Edited on 10/4/14 by tegwin]

[Edited on 10/4/14 by tegwin]

Aren't there companies who specialise in "adjusting" odometers?
Presumably they can adjust to your requirements?
Cheers, Pewe10

Ferris Bueller.....great film!

Perhaps you should buy a huge house and garage in US, overlooking a ravine....as you want to ADD miles you should be fine, I think that's where he went wrong!

[Edited on 10/4/14 by McLannahan]

Sure there are companies who can wind it forward for a price.... but I want the locost solution.

It might handle more than 180 mph in which case the time would be halved....


Any thoughts on the signal?

Simple square wave should do just fine. Will probably handle lots more than 180 mph, the needle just won't move that far

Worth a try.... do you recon its a 5V ref on the signal or a 12v?

Start low and see... or measure the signal on the car that you are replicating.

Lot of faff if you ask me.

Just write the current mileage on the clock face along with that date you changed the battery and slap it back together

The really daft thing is that what you are doing is actually illegal! When I needed a speedo replaced, I found out that it was fine to replace it with a new one, but adjusting the new one to match the old mileage is classed as clocking - crazy!

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Originally posted by SteveWalker
The really daft thing is that what you are doing is actually illegal! When I needed a speedo replaced, I found out that it was fine to replace it with a new one, but adjusting the new one to match the old mileage is classed as clocking - crazy!

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Originally posted by nick205
Lot of faff if you ask me.

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Originally posted by tegwinalthough even at 180 miles an hour its going to take 300 hours....

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I don't think that the battery is needed to remember your mileage - it's much more likely to be stored in an EEPROM?

Nope... That'd make too much sense.... The battery keeps the memory on ram... Doh!!

Barking mad!

Quick google brings up this - not sure if it's the same model but one post says that ETB reset the correct mileage during a £25 refurb?

http://www.pistonheads.com/gassing/topic.asp?f=8&t=890931

Aye.. That's the one..... Was rather hoping I could wind it forward myself. Still not sure what signal it's expecting.... Hmmmm. Gnd and 5v seem to do nothing... Tad hesitant to poke 12v in there incase I melt it!

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Originally posted by gremlin1234

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Originally posted by tegwinalthough even at 180 miles an hour its going to take 300 hours....

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in archaic measurements that's approx 360,000 furlongs per fortnight.
just leave it as zero
edit maths...

[Edited on 10/4/14 by gremlin1234]

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Furlongs per fortnight, now that takes me back to my Uni days when it was noted that Kinematic Viscosity can be measures in Acres Per Fortnight, illustrated by the speed at which treacle spreads out on a table top.

Get a multi meter out and measure what you have on what pin on the car. It could well be quite a few pulses per mile.

There is probably some way to program the processor directly but.......

Figured it out..

its a 5V signal.... unfortunately even at the highest frequency the odometer will accept (just over 500mph) it would still take over 4 days to reach the required mileage..


I think I will just leave it at zero...life is too short Need to put the car back together as its supposed to be sunny tomorrow and I have a girl to try and impress

[Edited on 11/4/14 by tegwin]

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Originally posted by tegwin
Figured it out..

its a 5V signal.... unfortunately even at the highest frequency the odometer will accept (just over 500mph) it would still take over 4 days to reach the required mileage..


I think I will just leave it at zero...life is too short Need to put the car back together as its supposed to be sunny tomorrow and I have a girl to try and impress

[Edited on 11/4/14 by tegwin]

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Ok maybe I was optimistic that it had a processor, The HFC4518be is a binary coded decimal counter, and the MAF115 is a Czech build tachometer driver presumably use to convert the pulses to analogue speedo output.


http://katalogy.ic.cz/MAF115.html


Beaten to it

[Edited on 11/4/14 by DW100]

I did wander if it was possible to inject straight into the counter circuit but I don't want to risk breaking the speedo....

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Originally posted by tegwin
I did wander if it was possible to inject straight into the counter circuit but I don't want to risk breaking the speedo....

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Thanks for the comments!! I was trying to make things more complex than they need to be. Once I started looking at the display unit it became apparent that it is quite a simple device.

Used a 1Khz signal to wind forward in about 4 mins



Soldered a temporary wire (yellow/red) onto the signal pad and away we go!



The painted the bezzle, cleaned the glass and reassembled the entire thing


Proper job! Thanks all

[Edited on 11/4/14 by tegwin]

quote:

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Originally posted by tegwin Once I started looking at the display unit it became apparent that it is quite a simple device.

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