Gear Postion Indicator

Thread Starter


Joined Aug 5, 2007
Hi All. first post
I am a newby to this game. I am after using a 7 segment LED to indicated the gears.
My car has a cable controlled gear lever, as I change gear the cable moves in length.
What I am after is a way of taking the output from 7 reed switches in a row to along side the base of the gear lever with a magnet connected to the cable itself, so as i change gear the magnet moves and so operating a different reed switch.
This would require eight wires one connected to all seven reed switches (the positive lead) on one side and the other seven going back to the control unit.
the control unit it self is what I am after.
This would consist of the 7 seg led and the led driver, each reed swicth would give a different input to the driver cct perhaps an arrangement of gate that would give the output to the led driver so it would indicate the gear that I am in.
Using the standard form on a 7 seg led the 1st gear would turn on the segments "b & c"
the 2nd gear would turn on the segments "a,b,g,e, & d"
3rd would be "a,bc,d, & g"
4th would be "f,b,g & c"
5th would be "a,f,g,c & d"
Neutral would be "a,b,c,d,e & f"
reverse would be "a,g & d"

I know its alot to ask but can some kind soul please help.


Joined Aug 4, 2007
Nothing as complicated as a bcd driver is required.

Simply connect the wire coming from each switch to the anodes of a group of diodes with the cathode of each diode connected to the appropriate segment connection on the LED via a current limiting resistor. Sometimes people use only one resistor in the common cathode (or anode) connection but the segment brightness then varies depending on how many segments are lit and may be uneven between segments if the forward voltage drops of the segments are slightly different and resistors aren't expensive.

Actually I would tend to wire the circuit the opposite way to minimise the amount of live (12V +ve presuming your vehicle battery has -ve connected to chassis) wiring running around. I.e. I would connect the common side of the switches to ground (chassis) the switch wires would then be switched negatives, if the insulation on a wire failed it would simply turn on unwanted segments and cause a weird display rather than blowing fuses.

In this latter case you would simply require a common anode rather than a common cathode LED. Anode connected to a fused +ve, then a resistor from each cathode followed by the diode matrix (anodes towards the display and cathodes towards the switches) and then through the switches to chassis.