[MilesPerTank]

I took some measurements on the currents with a current probe and scope.

brightness zero 37mA
brightness one 55mA
brightness two 73mA
brightness three 90mA

I can see that base pin is being PWM'd at 500Hz. Peak current is 90mA for all but brightness zero (no base current pulses). Above I just wrote out the mean currents.

So at full brightness you're looking at :
*65 C/W for junction to air unheatsinked 7805 TO220 package

(( Vin - Vdiode - 5V ) * 90mA ) * 65C/W = rise over ambient

Plugging in Vin =14V, Vdiode = 0.7V you get 48.55C. Max junction is 125C. As long as you're under (125C-49C =) 76C / 166F ambient you will be Ok.




I also hooked up a function generator for a variable pulse width square wave to make sure the pulse is being detected properly. What is your idea behind the IC or rpm variable? I fed it a 10Hz signal and the IC was 20. 50Hz the IC was 100. Etc....