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Turn signals on my motorcycle....

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frog

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Ok, I just got some new flushmount LED turn signals for my bike. The stock ones have running lights and turn signals (three wires). Now, the new signals only have positive and ground.

Now most people just use the turn signal and ground wires and leave it at that. I'd like to have both working.

There is a product out there called the magic blinker that will work...
https://www.customled.com/PRODUCTS/MAGIC_BLINKER/magic_blinker.htm

but I'd like to make one. It's been a while since I took transistor theory, but would a p-channel mosfet work? Using the turn signal as the gate and the running light wire as the source?
 
N-channel MOSFET (NMOS) is cheaper, more efficient, and common place than a PMOS. Using this requires that you attach the NMOS in series with the light such that the NMOS is closer to ground than the light (with the light being on the "drain" side of the NMOS). Should it be required that the NMOS be closer to +V than the light, then you should use PMOS instead (with the light being on the "source" side of the PMOS).

In either case, just make sure you that it's source-drain voltage is high enough to operate in saturation and that it's gate-source voltage is high enough to activate the transistor. You'll need something like a timer to sequence the gate voltage so the light blinks on and off.

I don't know much about the semiconductor timeline or when you took transistor theory, but NMOS has overtaken PMOS as the most common and preferred MOSFET (except in complimentary IC design), should it be the case that PMOS was preferred when you took your courses.

An alternative, depending on how much current your LEDs consume (probably too much: an IC-based LED controller
**broken link removed**
You probably won't go this way because this particular chip works through a serial protocal, and the bike voltage is probably too high.
 
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Yeah i just figured pmos because if you were to tread the flasher signal as a square wave... when its off, the running light is running and when its on, the running lights are off, hence, creating a flasher effect using the running light source....

if that makes sense
 
?

You mean so that you don't have to build a separate mechanism for the flasher and can combine it with the proper activation for the running lights? Whatever works for you ;).

Running lights...those would be the lights normally on when driving? I have no idea how wiring works in a motorcycle (or a car for that matter).

Efficiency of the NMOS vs PMOS isnt too big in this case. Its just some lights, not giant motors or anything. The "square wave" is already generated by the bike? If so, that definately makes things super easy for you. Good luck!
 
There is a "cheap & dirty" way to do this, given two conditions. If your running lights are on all the time, and you have an electronic flasher ( requires no load to flash ) you can do it with a small SPDT relay.

All you do is connect the lamp to the common of the relay, connect the running light wire to the normally closed contact, and connect one side of the coil to the signal light wire. The other side of the coil goes to ground. What will happen is the running lights are powered, and when you turn on the signal light, the relay operates, turning out the light.

If you want to go one step further, you could put 2 suitable diodes in series with the normally closed connection, and connect the normally open to the lamp. This will dim the lamp for running lights, and give full bright for signal.
 
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