I've got an idea but I don't know what I would need?

Projects General Guidance
1

So I want to build a programmable flasher relay for my 97' BMW 328is. There are 2 things I want it to be able to do. The first is I would like to switch all of my turn signals to LED bulbs which they do not make a correct flasher relay for this already. The second reason is I'd like to add the "One Touch Turn Signal" feature like a modern BMW has for switching lanes (basically you click the lever half way and let go and the signal blinks 3 times)

I would like this to be integrated inside of a gutted factory style relay housing, it's a double height relay so it should have plenty of room. I would like to build it robust enough to handle both halogen and LED bulbs. It will probably need to be able to handle up to 15 amps. Seems that if I had 2 small relays controlled by some programmable device with several inputs that this would not be too difficult.

6 inputs:

12V constant
Ground
Left Signal
Right Signal
Hazard
Crash Module (turns hazards on if airbags are deployed)

2 Outputs:

Left Side
Right Side

Each side outputs to 4 lights, 2 are the main "high amp" signal bulbs and 2 are small bulbs that would probably draw less then half an amp combined in the instrument cluster and a side marker. Realistically each side should draw less then 5 amps but the main fuse for the system is a 15 amp fuse (granted that's because if you have the hazards on it will turn all of them on at once).

I don't believe this is a very complicated project and probably a very easy thing to program for a newbie like myself. I believe I could likely use an Arduino Micro for this rather easily? I just don't really know what's best to convert the outputs from something like the Micro to a high amp circuit. A typical relay will likely be too large but I don't know much about Solid State Relays.

Any and all help will be greatly appreciated!

2

@silvers4sarefaster

Welcome to the forum.

You may get a few members to suggest ideas to help you out ... you are going to need to spec some external relays or power FETs for the switching of the high currents for the lights.

But, in general, the forum does not generally become involved with automobile/motorcycle safety devices of which I believe your blinkers would be considered. The reason is simply that modification from factory (or authorized resale devices) could invalidate your liability insurance or could leave you with a significant liability in the event of an accident - say, you engaged your left-turn signal to pull into traffic but the Arduino reboots.

Designing for automotive, airplanes (excepting experimental), and potentially home HVAC is often classified as unauthorized modification to 'approved' construction. Burn your home down, sink your boat, or crash your car due to the installation of a home-brew add-on or replacement device would be regrettable and doubly so if human life was lost.

Many members will choose to disregard the issues and assume the responsibility, but at least you need to be aware of the (potential) consequences of your actions.

Good luck,

Ray

3

DOT regulations are written as such that the builder of the device must design it to meet the regulations but there is no certification process. So if my build meets the regulations as many aftermarket LED relays do then it is technically DOT legal. I would rather use a chip that cannot reboot and is just a simple programmed chip, I just don't know what that would be? It only needs to be programmed to flash a minimum of 3 times with a left or right input and if constant input is received and it flashes more then 3 times it immediately shuts off. I'm sure there is a very simple chip that can be programmed to do this.