136: Sunday 18th April 2010

I mounted the fuel gauge circuit on the back of the cluster, but the gauge did not work. I tried all sorts of different configurations and the problem was due to the gauge mode of operation where it measures a low resistance to ground from the fuel sender originally, so the voltages were arbitrary. In order to make this work I needed a PNP power transistor configure as emitter follower from the output of the circuit. Then disaster struck, I was taking the gauge from the cluster and I dropped it and broke the needle shaft. There was no way to repair it, so I needed a new plan.
I thought about just getting another cluster, but decided to use the fascia and mount 10 LEDs around the edge to make it a curved bar graph display. That will look much cooler too and be easy to read. I will have 4 red LEDs at the bottom end, then 3 yellow and 3 green. I went to my local electronics shop and bought an LM3914 bar graph display driver, but they did not have the LEDs I wanted. I have ordered them on-line and now have to wait for them to arrive. I already had an LED bar graph matrix of 10 LEDs in a rectangle mount, so I built the circuit on a prototype board and tested it. That worked o.k. so I then made it up on some strip board and mounted it in the box that I had for the old circuit. I have threaded this through the centre console and calibrated it to show the right number of LEDs for the state of charge. I have a 1000 micro-Farad capacitor on the 120V supply that keeps the voltage when the throttle is pressed, and recharges when the throttle is released. The level does drop off when driving, but it comes back instantly when the throttle is released, so this is just a quirk that I will have to get used to. Anyway the temporary set-up is now in use and working well, so when the LEDs arrive I can work on mounting this all in the cluster. It is difficult to make out the LEDs in the photo, but they are there in the white rectangle in the black box hanging out of the centre console in the photo below. All 10 LEDs are "on"as I had just charged up the batteries and the display on the programmer is reading 132.3 volts. I have temporarily mounted the programmer unit on my Tom-Tom bracket on the air vents as it was getting in the way down by the gear lever. Fortunately it flips up so I can still adjust the volume on my stereo.

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