Formula Car Gear Circuit

VT Shift Circuit ConnectionsMy brother is senior at Virginia Tech and is a memeber of the VT Formula SAE team which designs and builds vehicles for national competitions.  This week he told me the driver was having a difficult time managing the car and knowing what gear they were in.  One of the team members suggested a shift monitor that could read an analog signal from the engine and display the current gear.

There is a poteniometer attached to the transmission that outputs voltages in different gears.  Since the transmission voltage ranges are not uniform between gears I used a ATMega8 microcontroller with onboard analog to digital converter to read the voltages and determine the proper range.  Here are the ranges (btw, there is no gear 1)

Gear 1 – Display 0 – 4.88v to 5.00v
Neutral – Display 0 – 4.40v to 4.88v
Gear 2 – Display 2 – 3.80v to 4.40v
Gear 3 – Display 3 – 2.00v to 3.80v
Gear 4 – Display 4 – 1.00v to 2.00v
Gear 5 – Display 5 – 0.26v to 1.00v
Gear 6 – Display 6 – 0.00v to 0.26v

The dash on the car has very limited space so I separated the 7-seg from the control circuit.  Seperating the 7-seg the control circuit can be in a box away from the driver and the small display mounted on the dash.

Here are a few photos of the setup

And also a demo video of how the system works

For those interewsted in the code, here is a link to a ZIP of everything.  This code compiles on linux using gcc-avr and can be downloaded to an ATMega8 using a Dragon AVR USB programmer on Ubuntu if you have avrdude installed.  Also, here is a schematic of the final circuit.

1 Comment

  • By JamesD, June 11, 2009 @ 4:02 am

    Thanks for the useful info. It’s so interesting

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