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gear indicator wiring HELP

boothybunch

Mar 23, 2011
1
Joined
Mar 23, 2011
Messages
1
Hello out there,

I am new to the forum and have a problem my head can't get round.

I have just dropped a K75 bmw motorcycle engine into a reliant fox car. Double the horsepower, double the fun biggrin.gif

anyway, The bike engine has a gear position switch on the gearbox which uses 4 wires.
yellow / black, Yellow / blue, Yellow / white and a common black earth. Combination of the wires shows which gear your in. I am looking to install a standard numerical display on the dashboard to show the gear, but I can't get my head round (probably down to still wiring the engine electrics)

The numerical display that I have chosen is already Pre-wired with the colours below. the display has a single wire for power then has numerous wires that when earthed show the number or N for neutral.

this is the list I have got for the wires. Bike wires on the left, indicator on the right

Yellow/Black and Yellow/White grounded = 1st gear - Brown & Yellow: 1st Gear

Yellow/Blue and Yellow/White grounded = 2nd gear - Black & Green: 2nd Gear

Yellow/White grounded = 3rd gear - Green & Blue: 3rd Gear

Yellow/Blue and Yellow/Black grounded = 4th gear - Yellow & Blue: 4th Gear

Yellow/Black grounded = 5th gear - Brown & Red: 5th Gear

Yellow/Blue, Yellow/Black and Yellow/White all grounded neutral - Green


Any ideas how to do this and give my head a rest??? Do you think I need to make a PCB, microcontroller to sort this or can it be accomplished with relays?

Thanks in advance
 

Laplace

Apr 4, 2010
1,252
Joined
Apr 4, 2010
Messages
1,252
What you need is a 3-input/6-output decoder where the six outputs will drive six relays or transistor switches that will ground the six inputs to the display device. The 3 inputs will interface to the 3 transmission outputs and be inverted as necessary. The decoder can be implemented with dual and triple input CMOS logic gates, and should be done with about a half dozen chips.

To design the decoder, you will need to work backwards from the display device. Create a 6x6 matrix showing wire color vs. display state (N,1,2,3,4,5). Then for each display state place an 'x' for each wire that must be grounded for that state. Now draw a 3-input Karnaugh map for each display wire color. The 3 inputs will be the 3 output wire colors from the transmission. Each display output state will correspond to a particular combination of these 3 inputs. Now transpose each 'x' for each color in the 6x6 matrix to its proper place in the Karnaugh map for that color. Finally, translate each Karnaugh map into the logic gates to drive each display wire. The logic design process is tedious but simple.
 
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