I would like to make a small hobby project to implement in my car. However, I would like to ask here as I do not have much experience with electronics.
Let's suppose that I have a switch which should turn on or off the daytime running lights (DRL) of the vehicle. These are separately installed and are consuming ~0,8 A from the battery (14,4 V when charged).
I would like to achieve the following effect (we assume that the ignition is turned on):
- when I close the switch and the engine is not running, the DRLs are off;
- when I close the switch and the engine is running, the DRLs are gradually turned on (fade-in for about 5 seconds (configurable));
- when I open the switch or the engine stops running, the DRLs are gradually turned off (fade-out for about 5 seconds (configurable)).
To me, it should be something like this:
I think the schematic can get information whether the engine is running via:
- a voltage comparator - preferable, as it should be simple enough. If the car battery voltage V1 is above a certain (configurable) threshold, e.g., 13,3 V, then turn the rest of the schematic on;
- an inductive tachometer - shall be a bit harder and comprehensive to install.
Perhaps a time delay relay may also be used, but would not be very suitable as it wouldn't detect the engine stopping.
As possible solutions for the fade-in/fade-out effect, I though of a BJT with a RC (integrating) circuit to set the time constant. Nevertheless, perhaps the losses would be lower if a (MOS)FET is used because of the ~10W LEDs. I also read that a 555 in monostable mode would be suitable.
It is important that the transistor is positioned "high-side", i.e., it opens or closes the 12 V supply to the DRLs. Their negative pole is connected to ground (chassis) and the positive is currently fed through the simple on-off switch SW1.
Preferably, the solution should be as simple and inexpensive as possible, i.e., no Arduinos or microcontrollers if feasible :)
Thank you in advance!