I am doing a tacho-meter of a single 12V power supply, it is meant for a car engine. However in real life the power supply from an real vehicle fluctuates between 10-14V. In this situation it is clear that some form of power supply regulation is needed. I am currently considering a Zener diode (zener regulation); but if so the breakdown voltage (or the zener value) has to be lower than 10V, which does not meet the 12V supply requirement. Are there any more suitable power supply regulation that can deal with the fluctuation? Say, make 10V to 12V and make 14V to 12V? Hope you understand my questions! Thanks all!