Step 2: Building the Clock Circuit
Since the clock controller is built onto a perf board you have lots of flexibility on layout. Construct the circuit according to the schematic diagram. The PIC Microcontroller will need to be programmed with the Multimeter Clock firmware using a PIC chip programmer. When powered up the blue LED will give you a visual indication that things are working, during the power up phase the LED will light steady and as soon as the clock is running it will flash on for one second and off for one second.
The firmware was written in PICBasic Pro so you will need that language if you wish to make changes to the existing functionality. There is still about 20% of the 2K PIC code space still available so there is lots of space for some hacking.
The meter faces of the multimeters will need to be updated to show time scales. I used a program called MeterBasic by Tonne Software. To make a new meter face all you need to do is enter the measurements of the meter face, the name for the meter and scale information. In the end you have a perfect matching scale for your meter. You can download the Hour, Minute and Second faces that I created for this clock here.
Here are the parts you will need.
1 X Pre-programmed 16F628 chip.
1 X 18 pin Chip Socket
1 X 2X3 inch perfboard Circuit Board
1 X 2 position Terminal Block
5X 1N4401 Diode
1 X 100uF 12V Filter Capacitor
1 X 47uF 5V Filter Capacitor
1 X .01uF 5V Decouple Capacitor
2 X 22 pF Crystal Oscillator Capacitor
1 X LM7805 5V Regulator
1 X 20 mHz Crystal Oscillator
4 X 4.7K Ohm Resistor
1 X 1K Ohm Resistors
3 X Tactile Button
2 X 0.1 inch pin header (2 position)
2 X 0.1 inch shorting jumper
1 X Blue LED
1 X 9 to 12 Volts DC Power Supply
3 X Analog type Multimeters, preferably with a 0.5mA setting