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Old 06-22-2010, 04:25 PM   #9
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Join Date: Oct 2009
Location: UK
Posts: 1,030
My Ride: 1999 328i
Originally Posted by Nachos23 View Post
l I'll check a couple of Trans specs to make sure it'll sink the required current (not sure what that is yet; will measure); it'll be based on visual appearance of the LEDs during day and night operation.
Any old transistor will be ample. BC327 or something. The junction on that will be able to sink up to 0.625W or 800mA. The LED's in the knob look like 20-50mA jobs. No problem at all for a common PNP. You may even be able to get a multi-device single part and have less of a rats-nest in there.

Originally Posted by Nachos23 View Post
Might install variable resistor initially so I can play with voltages...
I'd say a max of ~5V is a good idea. They will look much brighter in the car at night than on the workbench, and will last longer.
Originally Posted by Nachos23 View Post
Your design is great, but it actually has to interface the e46 shift selector to operate the lights in the DCT shifter (so not quite where you placed the circuit
From your first post, I understood there was a unique ground connection made for each position of the gear lever, and that is shown in the diagram as the switches marked PRND. As each switch is closed as you move the gear lever, it grounds that individual transitor base, turning on the 5V to the knob for the LED of your choice.

All the others are pulled up to 5V by the 10K resistor pull up, turning them off. This is because just (5V-0.6V)=4.4V on the base will light the knob LED. Although you say the line floats to 7V, so you may not need the 10K, as touched on in post 4.

Last edited by Arty; 06-22-2010 at 04:31 PM.
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