DIY

CIRCUITS

ANALOG AMP METER CLOCK

Elegant timepiece marks the hours with needle meters. By Gene Scogin

Photography by Gene Scogin

Several years ago I had the idea of making an analog clock that used voltmeter-style needle gauges rather than a standard dial. A few weeks ago I finally made one, using an Arduino board and 3 current meters from a local electronics store. I built it up in stages, starting out with a single meter that displayed just seconds, then adding hour and minute meters, adding buttons and programming to make the time settable, and finally building it into a nice box. Here’s how I did it.

Feeding the Meter The Arduino board has 6 outputs that can drive analog values using pulse width modulation (PWM). This means they simulate output voltages lying in between binary high and low (0V and 5V) by cycling rapidly between the two for varying time ratios; for

example, a 2.5V output would be simulated by being on for exactly half the time. I found that the Arduino’s pulse frequency was fast enough (490Hz) and my meters were slow enough that you could drive them directly from the board’s outputs without the needles vibrating; you don’t need a capacitor to smooth out the signal.

I was only able to find ammeters and not voltmeters, so I needed to put a resistor in series with the meter to limit the current. Ohm’s law states that to get 1mA of current with a voltage of 5V, you need 5,000Ω of resistance. To allow for normal variations in components, I assembled this resistance by putting a 4,750Ω resistor in series with a 0Ω to 500Ω potentiometer. To set the range for each meter, you first zero it with the adjustment screw on the meter itself, then adjust the pot to set its high point.

Make: 165