Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
I made a digital tachometer for my car, which you can see **broken link removed**
A digital speedometer is a bit more complicated and will require you to be able to program a chip. have the start of plans for one, but I've never bothered to try it out so it might not work. Who knows. You can email me for the details on that if you want to give it a try. Personally, I'd just buy one already made like Dakota makes.
All your other gauges are really just voltmeters, calibrated for the output they expect to see. For those some small variations of your favorite voltemeter will cover all of them.[/url]
Unfortunately that is where you're going to have to be creative and know something about your car too. It *should* work on any car, but fitting it will probably require modification if it isn't a modern, fuel injected, 4-cylinder model. Even if it is, there will probably be things that need to be tweaked. You'll really want your factory service manual for the electrical diagrams. Without that I would have never succeded.
The input signal on my car comes from a diagnostic connector under the hood. If you have a connector for a tachometer used when tuning up the car then that's where this goes. The difference in my schematic for Miatas is that in the early models the signal was positive, while in the later models it was negative. That's where you see the year note in that diagram.
The PDF for the LM2917 has great examples that you can use, as well as a formula to determine some of the resistor/cap values depending on how many cylinders your car has. Below is a copy/paste that somone else used to illustrate:
Vout can be found by using the formula:
Vout = Vcc * R1 * C1 * Fin
Where Vcc is the supply, Fin is the frequency input.
It is a good idea to make R1 a variable resistor. On making the circuit you may find that the output of the chip isn't quite right, twiddling the value of R1 helps to get the right output.
If you choose values of Vcc=8, R1=40K, C1=47nF and Fin=266 then the output is 4 Volts.
Therefore if the output is linear then we have 1V for every 2000rpm.
Basically, if you have a 4 cylinder model then you can just copy my setup, but if you have a 3, 5, 6 or 8 cylinder model then you'll have to use that formula to determine the correct values.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
