Hi!

I'm new to this site and, for the most part, to circuitry and electronics. I have a vague understanding - I know about wattages, voltage, resistance, current and how these interact in a fundamental sense - and have some ideas as to how I want to go about this project, but there are a looooooot of things I don't know.

To start off let me tell you what I'm doing.

I want to retrofit my cars taillights with LED arrays, most likely attached to some sort of flexible breadboard type thing (don't know what it is, but I've seen it. It is like a silicone wafer with perforations for through-hole components) inside the current taillight fixture/casing. Now, I found some suitable LED's at 3.2V and 20 mA, and I am currently estimating 100 per light (total of 200). The taillights will be parallel circuits composed of multiple two-LED series, I have calculated resistance to be 300 ohms at 1/4 W. The entire thing will likely plug straight into the car's current infrastructure which would mean I am running 12V (with typical variance of a car battery being 12-15 right?).

The running lights and brake lights are to be passive which brings me to my first concern: I Don't Know About Them Rectifiers.

I know I can use rectifiers to switch between two *circuits* (same circuit different resistance: brake lights at 300 ohms, running lights at maybe 500-600 for half the current?), but I don't know what else rectifiers do in a circuit. Do they consume wattage? (there must be some thermal waste...) Do they affect resistance? (it is, after all, another object in the electrical path)

Once I have of course sorted that out, the next step would be to create an array of LED's for my turn signal that animates when I activate the handle by the steering wheel. That will be a completely different discussion of Arduino programming, but this brings us to my second concern: Is My Understanding of Logistics Sound?

If I tap onto the wire going to the turn signal, do you think it would be a straight current with the light bulb flashing, or is it already flashing coming out of the computer? (This is a 1997 Infiniti if it changes the understanding of how the lights work). My idea was to simply use that wire as an input for the Arduino, and trigger the animation for the turn signal.

I know this is a really thick forum post, especially for an AAC virgin, but I hope somebody - or some people - can help me out.

 

Soooo, how long does it take for people to reply on the forums? Orrrr is AAC dead?

 

OH! I get it. The internet doesn't like to read.

TL;DR
I need to safely use 12.7-14.5V DC as an analog input on an Arduino which only takes 3-5V. Help?

 

It's a little hazy as to what all your questions are.
State them in reasonably short sentences and I'll take a shot at them.

To drop a high voltage to a lower voltage for the Arduino input, you can just uses a resistive divider consisting of two resistors in series.
For example a 32kΩ resistor in series with a 10kΩ resistor to ground will drop 12.7V to about 3V.
A 10μF at the junction to ground will help filter any transient voltages from the Arduino input.

Standard diodes/rectifiers drop about 0.7V when conducting and will dissipate about 0.7V times the current through them.
Schottky diodes are a little more efficient and drop about 0.4-0.5V.

 

That actually answers my questions(both), Thank you!

 

Regarding your (third?) question about the turn signals, they are usually powered by a relay - i.e. you get a 12V current for a second, then no current for a second, then 12V again.. etc.
You might have to trigger your Arduino to animate on the first 12V signal and then keep a track of subsequent pulses to detect when the turn signal is finished/aborted/switched to the other direction. Bit more complicated than I thought when I started this reply!!

Good luck!

 

Ah okay, that makes sense. Is there a way you can think of to trick the relay to supply a steady current?

 

Ah okay, that makes sense. Is there a way you can think of to trick the relay to supply a steady current?

You would need to bypass the flasher module to access the "input" signal to it and use that to feed/read on your arduino..

 

Cool, that sounds very do-able

 

You would need to bypass the flasher module to access the "input" signal to it and use that to feed/read on your arduino..

That signal may be the same for both right and left signals.

If so you will need the left and right signal voltages that come from the turn signal switch on the steering wheel column.

 

That signal may be the same for both right and left signals.

If so you will need the left and right signal voltages that come from the turn signal switch on the steering wheel column.

Yes.. sure could be..
Having the wiring diagram for that vehicle would be beneficial for them to see whats being switched and how/why,etc..

 

What year, Make and Trim is the car, I might be able to give a Diagram for the cars lighting If the OP don't have one.