led air conditioning

Hey guys, I'm looking for some help with a LED project I'm doing on my car. Heres my plan: I'm going to install red and blue LEDs inside the air conditioning vents in my car. Then I want to wire the LEDs to the air conditioning temperature dial in my dash so that as I change the temperature from cold to hot, the LEDs will fade from blue to red to display the temperature I have selected. Basically, as the dial turns from left to right, the blue led will fade to nothing, and the opposite for the red LED. If anyone knows how to do this, or knows where else I should go looking for answers to this, I'd really appreciate it. Thanks in advance -Jacob

Most likely your temperature selection dial is mechanical which means you will have a very hard time interfacing with it. It would be "cool" if you include a thermistor that actually measured the temperature of the air either in the car or coming out of the vent and adjusted the LEDs accordingly!Kevin Pierson

I thought about that, but I decided that would be annoying on really cold days or really hot days where the led"s might display a color based on the car air temp instead of what temp the air conditioning is set on. Is there no way to just use the dial to interface with a controller made for led's so that as it turns, it turns the color selection/fader on the LED interface? sorry if I'm being unclear

Again, not knowing what kind of car you are working with makes it hard to say what may or may not work.Kevin Pierson

Right, sorry. It's a '02 Hyundai Elantra GLS. If you think that the themistor would work well, I'll take your word for it and give that a shot but I've never worked with those so I'd need some help figuring out how to get it to fade between blue and red based on the temp

http://www.superbrightleds.com/pdfs/LDK-8A.pdf Could this somehow link to the dial on my temperature control?

Anything can be done with enough time and money. That is probably a fairly simple unit - a potentiometer connected to an Analog to Digital Converter pin on a microcontroller that controls a PWM output pin. It could be possible to replace the pot with a thermister and go that route. It would also be possible to replace the pot with a sensor of some sort that is connected to your dial. I can't say I know exactly what the dial in your car looks like. You will just need something to convert the position of the dial in to a 0-5vdc analog signal.Kevin Pierson

this is a picture I found online. does that help?

You should be able to use 2 thermisters - subtract the "ambient" outside temp from the room temp thermister (rectified if used for for heating). Then set for the desired "difference" in temp. Not ideal, but (maybe?) one step better than just measuring the temp. Then again, aren't most conditioned cabins usually in the 20°C to 25°C range, maybe 20°C-30°C? (ie, ranging near official room temperature = 25°C/75°F.) Ideal might be a mapped system using a PIC/AXE - that depends on whether the thermister "difference" principle works. Maybe use LM35 temp sensors (voltage proportional to Centigrade) for later displays (eg, a voltmeter or screen displays temp).