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May 4, 2011
Tutorial - Building a Digital Speedometer
about 5 years ago
I like this project, I’ve been thinking of doing something like this for a motorcycle because the original speedometer is getting a bit clunky.
But there’s one thing I would do different and that would be to use the factory speedometer, and output your speed to that.
This of course requires another project, but one which I have been looking into. If this car is like most, it will have an air-core movement driving the speedometer needle. To make it easier to figure out, I would cut all the wiring to this movement and wire-in an all new circuit using something like a CS4192 air-core driver chip (onsemi.com). This takes a serial input and calculates the correct polarity and voltage to send to the two coils in the meter movement.
What I have built so far is based on the CS8190, which uses an analog input to drive an air-core movement over 300 degrees. This is being used with an LC-1 air/fuel ratio controller. So I have a gauge that shows the A/F ratio using a nice 6 inch needle which used to be a tachometer from a Ford. It just happened to work out that a 5 volt signal put the needle almost exactly at the 270 degree position, so it ‘looks’ right. Then I printed a new gauge face on acid-free matte photo paper. I had to make a traditional light to show the gauge face at night because the factory approach illuminates the face from behind, but the needle is still lit-up the same way as originally.
What I want to do is use the digital output on the LS-1, to get better accuracy. So I’m trying to learn how to use digital signals. Not there yet…
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