Does anyone know what crystal frequency I would need to get in order to upgrade my speedo to a different scale? I saw on an earlier thread that the 200 MPH speedo uses a 7.3728 MHz crystal. But I doubt I would ever get my lil ol 85GT up to 200 mph. Maybe go to a scale like 140, or 160? Any info would be great!

Thanks,
Robert

Correct me if I am wrong too please, but the yellow arrow points to the crystal, right?

Thanks!
Robert

Sometime back I posted a $10 circuit using a 74LS628 VCO chip that will replace the crystal entirely. You can basically dial up whatever full scale you want.

I used it to make a Canadian 170kph and 140kph speedo read in MPH in my Ciera GT. There is enough range that a 200MPH (although a little pretenious) is possible.

Terry

Thanks for the info Terry, is the 74LS628 VCO chip readily available, and is it easy to install?

Thanks,
Robert

You would have to build a little circuit around it. About 10 parts (resistors and capacitors). The prices I've seen for the LS628 is about $2-3. I wouldn't both unless you are building a non-standard full scale speedo. This method keeps the odo and trip correct.

If you don't care if the trip and odo are wrong, you can rescale the meter itself with a pot.

I would like to keep the odometer and tripmeter accurate, but it sounds like it may be more than I am capable of doing, unless you have, or know of where I can get, some simple instructions with required parts?

What I am doing is installing the white face guage overlay. The guy that builds them can pretty much make what you want, so I was thinking about having him make a 120 or a 140 speedo face, and recalibrating my speedo. If it looks like it is going to be too complicated, I guess I will get the standard 85 MPH overlay, but it is so darn easy to get past 85, I would really like to have one that went higher.

Thanks,
Robert

[This message has been edited by robertjay (edited 11-10-2000).]

Too big, I'll email it to anyone that wants the schematic.

[This message has been edited by terryk (edited 11-13-2000).]