I have been working on an auxiliray directional lamp to operate with the dirction signal of my 40' box trailer. This lamp is to luminate the "wide turn" sign on the rear of the tailer to warn drivers behind me of my intentions so not to obstruct my path while making the tight U-ture with my trailer. Note this light should not be on for a normal turn. This project started with a series of 12v relays when a member sugested to use PICAXE to control the operation. Smart! This why I'm here.
With that said, this is my delema.
I wish not to re-wire the vehical, but use the existing 12v + wire that feeds the turn signal. By sending two (2) power on impulses as a triger to activate the light, and for the divice to ignor the constant on of the normal sinal (directioal light) operation.
I need to know if the chip can funtion something like this:
1 power on-wait (1 sec)-stop (note: More than 1 second wait time will be a conflict with the signals flasher)
I would agree that the board could have it’s own power such as 3 batteries that may need replacement over time.
My thought is to use the vehicals dirctional directional switch, and not add a new button or wires. By having a small board in a weather resistant box, it maybe abel to fit inside the tail light.
Regarding the on/off impuses. They would be from the existing turn signals wire as a code to trigger the chip to engage a relay to alow the same turn signal wire to power up the lamp. Note that this wire will flash once the flash starts, and so will the LED lamp with the turn signal/tail lamp.
Also in most cases the brake lite will be on…so it too could be used as a costant power source. True that running ligts are manditory at night, and not during the day.
Use your running light power to supply the board power. Add a line from your turn signal line to an input to your preferred microcontroller. Use the turn signal lever as a switch to signal your new sign to light at the proper time and then allow it to shut off after the turn signal stops flashing for a minute or more; however long you think is required.
If you use a PICAXE, you could get away with an 08(m/m2) or whatever the current version is. If you buy a board from Rev-Ed, you just want to make sure the voltage regulator can handle like 12v input. You will need a circuit (transistor?) to drop the 12v signal lead down to 5v for an input pin. And finally, maybe a relay circuit to turn on your sign when you request it to turn on.
Your program would do something like listen on the input line for a high pulse and then a longer than normal delay followed by a constant toggle meaning, hopefully, you have requested the sign to turn on. Once the input line is low, no signal flashing, for your predetermined delay, you turn the sign off and loop back to the top of the program cycling through to wait for the next time it is requested to turn on.
I did agree with all the atomotive electronic designs for automotive componants that protection is a must for spiking wild voltage. The control of the boards power from the running lights will be much more stable with all the lights inline already absorbing the peakes aswell. Good choice! I still will plan for the use of resisters, capasitors to smooth the boards performace as well as a line drop transformer to feed the board.
My learning curve will be the writing of the “listen” code fro the impulse(s) for the chip to shake hands with a relay. I plan to let a 12v mini relay do the heavy lifting on this project. It will handle the power load and the spikes form the lines flasher that is in it.
The first thing what pops in my mind is the cigarette lighter socket. You can just buy one of these Car-to-USB adapters to feed your board with the power for the logic.
To switch the light on only if you are doing a u-turn you could use a hall sensor on your steering wheel and count the revolutions which are less when you just do a normal turn.
