Lighting controlled by engine's RPMs

[dragwindsor]

Hey guys, new here.

I have this idea to put red LED lighting in the engine area of my Honda sportbike, but not in the normal fashion.

I'm trying to figure out if it's possible to hook the lighting up to the bike, or engine, in such a way, that when I'm idling, the lighting is barely on, and as I increase RPMs they would get equally brighter.

Kind of like the old bicycle lights that contacted the tire, the faster you went, the brighter they were.

If anyone can help me out, I'd really appreciate it.

Thanks

 

[kingofwylietx]

AFAIK - Modern tachs use pulses to determine engine speed, much like speedometers. The trick would be to find a circuit that could take the pulse input and give a proportional voltage output. I would think that by disecting a second tachometer, you may be able to get it to work (using the output voltage from it to power the led's & coupling onto the factory signal wire for input). However, I have no idea how much of a load it could handle......or if it would even work.

 

[CPF Dude]

I can think of a few ways to do this...
(1) Get an F-to-V converter which converts freq to voltage (these were used on older analog tachs), then manipulate the output voltage/current to increase LED brightness. ISTR a chip called LM2907 or LM2917 from my past life that was used for this, and the datasheets had fairly complete circuits.
(2) Use a microcontroller or microprocessor to count the frequency and output a varying voltage or PWM output (better IMO). The tricky part here will be getting a clean measurable signal from the ignition coil.

Depending on what your level of electronics expertise/comfort is, you may not want to to either of those, so ...
(3) Get an analog tach and hack it to get the analog output from the coil driver.
(4) Get a digital tach with a bargraph and wire a resistor to each bargraph LED and other ends together, so that as more segments come on it adds more current to the output, which would go to your LEDs.

(5) Thinking out loud here, I haven't tried this, but wondering that since you don't need a linear voltage or current output, then perhaps a simple very low-Q high-pass filter could serve as a basic f-to-v converter.

 

[Rock Ranger]

A F-V converter would be the best way to accomplish this.

Here is a link to a F to V converter datasheet:

http://cache.national.com/ds/LM/LM2907.pdf

Study some of the circuits shown on the sheet. They will give you some ideas on how to wire your circuit.

 

[2000mc]

sorry about being a naysayer but... isnt the point of the lighting for showing off? if you're actually riding at high rpm, you're probably going too fast for anyone to notice. if you're idling around and revving the engine time to time, it would likely be to short of time for anyone to notice.

aside from just having it on all the time... you might be able to strobe it directly off a coil.