Thread: Help designing gps speedo

I found the numbers I jotted down at 3 different speeds (they're pretty low as I had the car on jackstands and things were a little hairy freewheeling like that)

5 mph - 12.5 hz - 2.5 acv
8 mph - 18 hz - 3.61 acv
26/27 mph - 58hz 9.3-4 acv

so it looks like both frequency and amplitude changed with speed. not sure if the progression stays linear at high speeds but hope it helps.


and tach signal is 9v DC square voltage signal, if that helps too

Thank you so much wildmane, exactly what I needed to know.

I will head to a general electronics store today, and pick up some resistors and caps. Current prototype in my head:
-Arduino Uno PWM->Low pass filter (sine wave)->High pass filter (remove offset from sine wave)

Aruduino Duo would simplify this project, it has a real analogue output. That would cut down on components needed, so I ordered one. But I will start with a proof of concept before simplifying.

Good looking out, mane!

Np bros. Hope it works out.

I did it! I got the needle moving!

First I wanted to learn more about the scope. I tried out a chebyshef lp-filter,

That worked perfectly, and you can really see how glitchy the resolution is with this cheap scope.

I then gave up with the complicated true sine wave, and just wanted to test what happens when you hook up a highpass filter to an regular PWM output:


Would you look at that, small negative voltage peaks! I tried to input this crappy looking signal into the cluster, and to my surprise it worked!

Now I need to make a program that sweeps the cluster, will post a video when I'm done.

Things are looking good! Thanks again wildmane!

Here's a quick video

Haha dang, that's cool as shit. Nice work... crazy looking output on that high pass filter.

The hard part is done - GPS integration should go fairly smoothly on the arduino!

Cool stuff. We are getting ready to do the same thing with the VET auto transmission since it doesn't have a speed drive when you remove the AWD box. We won't be using GPS, just translating another sensor for the speed drive.

Nice work.

Awesome stuff Carlos!