Gear Indicator – MGZR Rally Car – Version 2

Wow it’s been a long time since I posted here apologies, I’ve just been doing a lot of engineering…..which I will now attempt to write up from scraps of paper and numerous logbooks.

After a successful set up running for a few journeys, counting gears and displaying them correctly, Adam has been having some issues with the gear indicator that I made for him. A quick diagnosis showed that some of the power supply debouncing caps had been rattled loose (rally cars are a harsh environment to engineer for!) which was causing some spurious switch presses to be seen by the msp430. This problem quickly manifested itself by counting gears erroneously.

While we were fixing the issue I decided it would be best to ‘re-invent’ the gear indicator system now that we understood Adams requirements a little better. Firstly we decided to go for a much larger 7 segment display, choosing a 25.4mm model that required a 5V forward voltage (2 series LEDs per segment). This is both bigger and brighter which will help Adam see the display in future events. This added some complication as the msp430 on the board runs a 3V3. To get around this I dug around my electronics collection and found a uln2004a (transistor array from TI), this allowed me to switch the 7 segment easily using the msp430 GPIO. As can be seen in the pictures 2 LDOs are now required but the main design hasn’t changed significantly.


The extra ICs (plus the fact we wanted a more robust solution!) has meant that for V2 I have switched to using breadboard. I should have done this in the first place really but hadn’t appreciated how much space I had to play with behind the dash. Note to self: fully understand requirements before inventing a solution. Hopefully this will mean the indicator will be less susceptible to vibration.

I also found some bugs in the code where I was setting up ports for the LED. These have now been fixed and the latest code has been uploaded below. Hopefully this final design will suit Adam’s needs, I will keep you up to date with his progress.


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