15 May 2008

Modification - the gauges

I've had everything out of my car for a few months. Now that I'm getting more time and energy to work on it I have to start somewhere. A problem I had with the car was the dysfunctional instrument cluster. Its a full detail cluster: speed, tach, temperature, fuel, and a full compliment of lights. But the first converters only hooked up the basic lights and the speedometer. That left 3 out of 4 of the gauges just sitting there. I want to use the gauges in some useful way. First off is to figure out where the wires are and what type of gauges they are. I probed and traced and probed and found very little. I found the temperature wire in the motor bay, but the fuel wire eludes me, and the tach wire is nowhere to be found.

I decided to tackle the tachometer first. I ran a wire from the cluster connector behind the dash out to the motor bay. Then using a signal generator I found I need 2 pulses per revolution to drive the gauge. Now I need to think of something to generate the pulses. After thinking and researching I decide to use the tail shaft on the motor (which is used to drive the A/C compressor via a pulley and belt). What if I put two magnets on the back side of the pulley and a hall-effect sensor or reed switch? Sounds good, so I chuck up the pulley in my 8x14 lathe and prep it for magnets. Then I take some scrap plastic and make mounts to protect the magnets and provide more area for adhesive. Add in two powerful magnets and you have a recipe for success right? I tested it with a reed switch and it worked pretty well! I need to make a bracket to attach the sensor still. I am still figuring out the sensor portion. I had a reed switch, but I broke it.

I'd like to make a drive circuit for the temperature gauge so I can monitor the controller or motor temperature (not sure which one yet). Thats still a future project. Similarly I'd like the fuel gauge to show a relative power remaining, but thats a complicated issue for later.

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