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Wanting to put red LEDs in the hood scoop of a truck so it looks as if the engine is "alive." Answered

I have a friend who wants to put red LEDs in the hood scoop of his truck. The truck is a Toyota Tacoma with a stock hood scoop. We want to have the system run so that the more RPM the engine experiences, the brighter the lights shine. There would be a baseline brightness (idling RPM) and a maximum brightness (4000-5000 RPM) Revving the engine would make the lights go from dim to bright and them back to dim when you let off the accelerator. What materials do we need? We don't want to make a flashlight type light with the LEDs but more of a glow. Are there certain LEDs that would be better suited for this sort of application than others? What kind of switch/wiring could we use?

Many thanks



Best Answer 6 years ago

mpilch has the smartest response; adding red to the front of your vehicle is downright dangerous, and if it isn't already outlawed where you are, it should be. Getting in head-on collisions because someone was confused at night and thought your scoop was the tail end of a motorcycle will make you have 'real bad day'.


You need to detect and/or count the frequency of the rpm, this can be done several ways...

then you need to control leds brightness based on that number.

It can be done with an entirely analog circuit, with all fancy logic design, but thats a lot of work. I would personally use an arduino or other microcontroller to do the lot.
The first part, finding the rpm there are 2 easy ways; 1: connect to the odb port (easy connector to source/make/fake) and literally ask the car computer what the rpm is. Other option is to work exactly like an aftermarket tachometer - clamp a wire around one of the ignition wires (to act as an inductor) and detect the current flowing through that (with appropriate safety circuitry - zener diode to knock down any high voltage pulses that would damage your uC).
Set up some code to count the rpm...

then scale that number to a pwm output to control the leds. Alternately, use an led controller and give instructions to the controller how to adjust the brightness based on your rpm. Something like the ShiftBright modules would be great for this...but you only need red.

I would suggest you find a red light that "blinks in time to music" and use your engine noise to trigger the intensity. That eliminates a lot of the problems you'd run into trying to interface with the tach or MAF sensor or whatnot... It would probably also be battery powered.

I'm assuming this is purely aesthetic anyway, so it's not like you need a direct RPM=brightness relationship to measure or anything.

If you want to build something on the same vane: http://electroschematics.com/2903/sound-controlled-lights/

Check you local laws. Some states/counties have laws against such lights. I've known people who have been ticketed for impersonating an officer because of those blue LED lights people use to put on there windshield sprayers. A friend of mine got pulled over for having a set of red Knight Rider style lights in the grill of his car. So have your friend check the laws. There may be restrictions on the kind of lights you can add and/or the color you can use.