I've got a simple 12v Red Led strip installed in my car, and i currently have it hooked upto a relay which turns it on when you unlock it from the key fob (the same as the interior / courtesy lighting) this was simple to do as everything was on the car already to create the circuit.

I would like to take this one step further and get the angry red LED's to turn on when I am driving angry. So using high revs, or high boost pressure (measuring the map sensor readings)

Would it be possible to use some kind of regulator or switch to control the LED's voltage based on a signal wire (either RPM, or MAP)

So my ideal would be, at 3,300 RPM I would turn on the LED's with 6v, then increasing to the full 12v at 4,000 RPM+ (its a diesel) or similar but measuring boost.

It might be a crazy idea, but I think it would be a fun project. Does anyone have any ideas?

Oh and the LED's are not under the car (fast and furious style) as that is illegal in the UK. They are positioned behind the front grill, so the whole nose of the car behind the grill is illuminated red. Looks really angry.

  • 1
    \$\begingroup\$ In the UK it is illegal to show any red light to the front. This doesn't matter if it's inside the car, outside the car, under the car, on the car, or even within the passenger compartment; if it's red you've broken a pretty fundamental theme of the Road Vehicle Lighting Regulations, 1989. The same applies to showing white to the rear, with the obvious exception of reversing lights. You can have any other colour behind the front grill. However, if the light source can be seen, you're also breaking the law. \$\endgroup\$ Dec 9, 2015 at 13:56
  • \$\begingroup\$ "illegal to show red to the front" ... with good reason, too. However, blue may also raise a slew of unwanted interest... \$\endgroup\$
    – user16324
    Dec 9, 2015 at 14:52
  • \$\begingroup\$ @BrianDrummond If it isn't flashing then there is no issue. No flashing lights, irrespective of the colour, are allowed anywhere on a (non-emergency/recovery/legitimate) vehicle except for orange direction indicators. Of course, if you were using blue lights to impersonate a police car or any other emergency vehicle then that's a different matter. \$\endgroup\$ Dec 9, 2015 at 23:19

1 Answer 1


AFAIK MAP sensors are available in two types - Analog and digital. Analog will give you an output voltage proportional to the pressure applied. Digital will give you a frequency proportional to the pressure. For our convenience (and tons of extra features), let's use a micro-controller (preferably arduino).

Analog MAP sensor: If the voltage is different than 0V-5V then first you need to convert the output signal to 0V - 5V output. Once you got 0-5V range signal, connect it to the analog pin of your arduino. From there, you will be able to get a value proportional to the output signal of MAP sensor.

Digital MAP sensor: If the voltage range is 0-5V, nice otherwise use an opto-coupler to do the logic level conversion. Something like this:


Connect the output to digital pin 2 of arduino. Now you can use interrupt based coding to figure out how many signal pulses you received per second (or per 10 sec). This again will give you a number proportional to the output signal of MAP sensor.

Now you have a number. When the number is high, you need the LEDs to light brighter or maybe blink at a fast pace and when the number is small, the light will glow dim or maybe you can add a slow breathing pattern.

To achieve this, get rid of electro-mechanical relay if you are using one and get a mosfet/power transistor which can handle the current required by your LEDs.

Read something about PWM.

Now all you need to do is to vary the duty cycle on the pin driving the mosfet/transistor. This will give you LED brightness proportional to the MAP signal output.

You can be creative and implement flashing lights, breathing lights or any other effect that you wish. Use RGB LED strip to get even more creative.


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