This Meter Clock uses a DS1307 RTC and Trinket Microcontroller to show the current time in style. The meters are PWMed into position directly from a few pins of the Trinket. The meters are ammeters that have had their scale replaced by Hour and Minute scales. You can see the scale adjustment calculated below, another alternative would be to do it in code as I did with the Multimeter Clock.Â
“For a 5 volt Trinket and 50 microamp meters, for full scale deflection we need a series resistor on each meter to keep the current less than or equal to the maximum current the meter can handle. Using Ohm’s law, R = V / I = 5 / .00005 = 100,000 ohms (100 K). You will need two of these resistors, preferably 5% or better tolerance. These are commonly available from electronics suppliers. If you want precision in calibrating the meter, you may want to substitute each resistor with a 100K potentiometer with a series resistor, perhaps 10 to 47 K. This allows for tuning the resistance. When I designed the project, the 100K resistors gave accurate enough time without needing potentiometers.”
