The Multimeter Clock consists of three multimeters, the first meter displays hours, the second displays minutes and the last displays seconds. A 16F628A PIC microcontroller keeps track of time and outputs a calculated current to each meter to display the current time.
The user enters the time by pressing three time adjust buttons. The first button increments the hours, the second button increments the minutes and the third button resets the seconds. Once the time has been entered the microcontroller will keep track of time from there. An interrupt fires every 10th of a second to increment a 10th second counter. Another routine checks to see if we have at least one full second of time, if we do the current time is incremented by a second.
The microcontroller has a separate output for each of the three meters. The meters are all in 0.5 DCmA mode, the negative lead of each meter is grounded and the positive leads are connected to a microcontroller output via a current limiting resistor. The resistor in this case is a 4.7K however this can be adjusted depending on the meter current scale available. Keep in mind that the PIC can deliver a maximum of 25mA to each meter so a meter with a lowest setting above 25mA would not work without additional circuitry.