Car voltage meter
My car lacked of voltage meter. Someone might wonder what benefits will voltage meter give?Of course, It'll tell what voltage does battery have. Since It is hooked to ignition switch, It'll tell us voltage right away on startup and how much voltage dips during startup.
Starting motor can take anywhere and even more than 200-400 amps, so dipping of voltage is acceptable during startup. But, what if voltage dips during longer trips?
That, tells most likely of alternator fault; alternator is not supplying enough current to battery to accommodate required load. Other fault apart from low-voltage, is high-voltage. I've encountered alternator fault when battery voltage rose up to 18volts. Obviously this doesn't bode well for 12v system, so I could add more load to make trip possible towards home. With load, voltage dropped around 14v so it was in safe zone.
Digital version
Right, now off to how I made it. Initially, I made 7-segment style voltage meter, but due sunshine, digits were impossible to read, it
Control circuit in digital version was bigger than in analog, since led-display needed control of It's own. I used AtTiny85, mikrocontroller, to control display and read battery voltage via voltage divider, fed to ADC (analog to digital converter). I don't have, nor need, AVR programmer. Instead, I used Arduino as ISP (in circuit programmer)
Analog version
Added benefit along with better visual readability during sunlight, is better UI during quick glace.It really doesn't matter is battery voltage 12 or 12.1. With analog meter, I just look and determine, Ok, It's close to 12.
Of course, I added something extra, and this extra was intelligent backlight, depending on voltage reading. This is accomplished by code, window comparator. I saved some space and few pennies when I used microcontroller to measure voltage and to control backlight leds.
Schematic is simple in analog version:
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