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Changing led colors using pressure switch. Answered

OK just to be up front i have no idea on how to do this so i would need the full story. i do know how to read schematics and can solder and most of the basic stuff. what i am looking to do is install led lights under my hood of my car in each of the snorkels that receive air from the outside. basically you can see down the snorkels to the engine. i want to install the leds so that when driving around under a no boost condition the lights would be green then when the engine get 5 psi of boost they turn yellow and then 8+ psi the glow red but with the higher the boost the brighter it gets so lets say at 10 psi the intensity gets brighter. like i had said i really have no idea how to even start this or what parts i am going to need. i can give you what ever info you might  like i know i will be supplying approx 13.2 volts as system is running but it is in a vehicle so the alternator does fluctuate depending on need of system.
if this doesn't sound fees-able please let me know and i can scrap the whole idea. it just sounded like a cool idea thank you



so if i understand this correct then maybe a MAP sensor would be the best way to go as it has a power ground and a sensor output in voltage do you think that is the right way to go? what would this all hook to? for programing?

You may be able to buy a second sensor and hack the signal like you were thinking.

Assuming the Signal could max out at 13.5 (ish) volts you will need a Voltage Divider to reduce the Signal voltage down to your logic level voltage (5v?)

Then use an Arduino to read the voltage level of the signal. You can use this signal to move between the different colors.

No boost = Blue, Lower boost like light Acceleration will fade to green. Then as the boost builds fade from green to Amber, finally to Red.

Like Iceng said, you have to learn to program first, or find a friend who can. Also should be noted this is *Definitely Illegal*....

So add a On / Off switch and be careful not to use it on the street...

Least not while anyone is watching anyway >.>

this is exactly what i am trying to do and believe me i know it is illegal i only intend to use it at local dragstrip. i do believe that the max out put of sensor wire is only 5v but i would need to recheck that. is the programing hard to figure out? any how to's? i figure maybe since i can program the vehicle maybe i can attempt this? what ardunio would i need? i really do appreciate all the help and hope my explainations are good enough to your questions

Well if your lucky there may be a sticker on it that will tell you, otherwise you will have to measure it while you're doing the run.


I'd start with a "Uno R3," on the Products page. or you may be able to find a local supplier. Also check out the Learning tab for a massive amount of documentation and guides. Instructables here is also a great place to search around.

Just break the project down into 3 steps, 1) Devise a way to read the sensor output. 2) Learn to program the Uno to use the Signal to blend the colors. 3) Use some 12V Led strips inside your scoop to light it up.

Btw I think it may be easier to Program if you stick to Green fading over to Red. Start 100% green / 0% Red, And as the Signal voltage rises you can use that to Adjust the Color mix.

Signal = 0V, Green = 100% and Red = 0%

Signal = 1.25V, Green = 75% and Red = 25%

Signal = 2.5V, Green = 50% and Red = 50%

Signal = 3.75V, Green = 25% and Red = 75%

Signal = 5V, Green = 0% and Red = 100%

There are ways to blend the color smoothly, but something basic like this will get it built. You can reprogram it later after you learn some more about how to use the code !

i didn't even see this answer. this appears to be the ticket. i will be looking more into this. Thank you so very much i really appreciate all the answers

Hey, No problem !

be sure to post a pic or two when you get something going :P

The MAP (Manifold Pressure) sensors I looked are a bit more then an analog voltage proportional pressure.

Depending on car they can be a SQ wave frequency proportional to pressure.

This is what i was able to find on the MAP sensor as it is a 2 bar MAP does this help any at all

The MAP sensor responds to changes in the intake manifold pressure. The PCM
supplies a 5-volt reference and a ground for the MAP sensor. The MAP sensor
provides a signal to the PCM relative to the pressure changes in the manifold.
With the key ON, and with the engine not running, the MAP sensor signal voltage
to the PCM varies between 1.5 volts and 2.5 volts. With the engine running, the
MAP sensor voltage to the PCM varies from less than 2 volts at idle, or a low
manifold absolute pressure and a high vacuum, to more than 4 volts at wide-open
throttle, or a high manifold absolute pressure and a low vacuum. The PCM
monitors the MAP signals for voltage outside the normal range of the MAP sensor.
If the PCM detects a MAP signal voltage that is excessively high, DTC P0108 will

Map voltage output is actually a pulsed waveform.


this is from the gm sensor i planned on using. 2000 Pontiac Grand Prix GTP 3.8 super charged 3.8l. i was not able to find a output wave form like you did for the ford maybe this will help looked to be pretty linear but i am not sure

Manifold Pressure
(relative sea level / absolute)2 Bar
MAP Output14.31psi / 29.01psi4.90V14.00psi / 28.70psi4.84V13.00psi / 27.70psi4.67V12.00psi / 26.70psi4.50V11.00psi / 25.70psi4.33V10.00psi / 24.70psi4.16V9.00psi / 23.70psi3.99V8.00psi / 22.70psi3.82V6.00psi / 20.70psi3.47V4.00psi / 18.70psi3.13V2.00psi / 16.70psi2.79V0.00psi / 14.70psi2.45V5.00inHg / 12.24psi2.03V10.00inHg / 9.78psi1.61V15.00inHg / 7.33psi1.19V20.00inHg / 4.87psi0.77V25.00inHg / 2.41psi0.35V29.10inHg / 0.40psi0.02V

You never said what temperature the inlet tubes get to ?

Or make of car ?

i am sorry it is a 1970 Cutlass Supreme with a 2004 LS motor swap and a twin scre blower on top of it. tipacally the inlet temps are 10 degrees coolor than what ever ambient temp is

It sould be possible to map the sensor data to a PWM signal.
So the higher the the sensor data the higher the PWM signal in terms of output.
That would take care of the brightness under pressure.
The color change can be done the same way, use two different maps, one for the lower values switching one color, the other for the high values and next color.
Biggest problem is to find a suitable sensor as otherwise you would need to do all the programming yourself.
Some sensors are designed for Arduino and come with the right libraries making all a bit easier.
Of course fully analog is possible too but very complex.

Maybe a LED power indicator could be modded?
If you can link the sensor data to a voltage signal the LED would show the levels accordingly.
Use a transistor instead of the single LED on the panel to drive your LED's.
Brightness can be done this way too by simply using multiple of the LED outputs with different resistors for your LED's.
Example: First LED is on and the transistor switches your LED to a dim state.
Next LED goes on and the corresponding transistor voltage is added to the LED output.
Might need a few LED status display and transistors but should work on a low tech level.


3 years ago

It is feasible depending on how hot your air intake nozzles get.

A pressure sensor that is compatible with a small microprocessor that will be on your side of the firewall, can be found. I suspect programming is going to be your major learn curve.

The LED color can be one RGB or three each of Green, Yellow, and Red.