I'm looking at starting my first project with arduino and figured I'd come here for guidance. Been a lurker for a while. I'm starting a sequential turn signal project, and figured I would run it by you gurus. I have a decent understanding on the electronics side (enough for this I think anyways) and I can solder pretty well, the coding is gonna be a learning experience. It's going to take the input "pulse" from the turn signal and turn it into a sequential signal with 7 sections of 4 led's. They run at 2.5v and 70ma each. I was looking at the mini since it is small enough to fit in the mirror housing. I'm planning on a small 5v reg to help keep the board cooler, and then a chip to step the output back up to 5v to the led's. My question is since I'm assuming (please correct me if I'm wrong) I will have to have a constant 5v to the arduino, would this hurt the board? It's gotta be able to be used when he car is off for lock/unlock and hazards. I'm just worried about it having power 24/7 and I live in az. Summers are brutal here. Any input would be awesome
Gonna use an LM78L05 to reg down to 5V and a ULN2803A to jump the outputs to 12v for the led's
You might want to just use an inexpensive 5V smartphone/tablet chargers used in cars instead of re-inventing the wheel.
Use the 5V for your entire project.
You're going to have to control transistors, or a shift register with high current outputs (TPIC6C595)
to sink 70mA thru the LEDs; a promini (or any '328P) can't handle that much current on an IO pin. The 4 LEDs can be wired in series if you have a 10-12V source of power.
TPIC6C595 is rated to 125C. I have some boards made up that like a Promini with Atmega328p-15AZ, which is also rated to 125C. Regular promini uses a part only rated to 85C.
Be sure that when you take the "pulse from the turn signal" you protect the input to the Arduino - I think what you are looking at is a +12v when the "pulse" (I assume you are leaving the existing blinker and using the output from that to trigger your circuit) happens. The Aruino can only handle a maximum of 5v on it's inputs and car electrical systems are notoriously noisy. I would recommend an RC network from the existing turn signal and a zener diode to clamp - say 47K resistor, 1 ufd capacitor to ground and a 4.7v zener as a clamp across the capacitor. The RC network takes the noise off the input and the zener clamps the input at less than 5v to protect the Arduino inputs.
I'm glad I asked you guys. I knew it was gonna be trickier than I thought. Oh well. More of a challenge, right? Trying to keep it as compact as possible so I can put it in the space inside the mirror, but I could find a way to run a few wires into the mirror on top of the power if I needed to
And just to clarify, it will be 7 groups of 4 led's that are in series. Probably use a 33 ohm resistor which would put me down to 60.6. Don't need full brightness, since originally the turn signal is illuminated by 3 led's, and I will be using 28. And as far as getting the 12v to the led's, wouldn't the ULN2803A work?