Re: Tachometer black box for magnetos, Attn byacey, lark2004 (DONE?!?)
So... I slapped together a PC board of this circuit and installed it in a plastic waterproof box with sealed strain reliefs for the wires. Works just fine, although I wish my tach drew a little less current, 80ma. without the dial lamp on; might have to rig up a charging system for my motor now. I added a .1mfd bypass cap for the opamp power supply rail.<br /><br /> I checked the calibration by hooking a full wave battery charger to the input where the points usually connect and ground. This provides a 120 Hz. signal that equates to 3600 RPM. My tach has a small adjustment pot for calibration that needed just a slight tweaking.
