Originally Posted by craftycoder
I am familiar with the idea of constant current. I guess I just fundamentally disagree with the common knowledge. The definition of a constant current is a constant voltage through a constant resistance. Therefore, using a resistor to limit the current is no more inefficient than using a constant current supply as the resistor doesn't use extra current, it just limits it which is all the active constant current circuit is doing.
All true if the "constant current supply" is not using PWM. The bucks use PWM ... if you are using that too to get your "constant current" then the efficiency should be similar.
Some systems for LEDs don't bother with a true constant current, they use the LED and light persistence to do the filtering on the PWM signal... leads to better efficiency.
A note on the horns...
On page 1 you said something like "One horn button - initial operation to the normal horn, after 1 second to the loud horn." Sorry but if someone wants the loud horn they want it now... not after any delay. In any emergency situation you want help NOW.
PS your definition .. well what happens if the resistance is not constant? EG a common light globe. Think about your Thévenin's and Norton's Theorems ! I stay away from definitions in most forums, they confuse rather than help?
There are some EMI regs that you may have to meet... FCC? Or some other gov agency.