Panel Meter Clock

I love the look of the old fashioned Box Simpson Meters. Have a look at this project that turns three meters into a functional clock! If that wasn’t enough it even synchronizes its time using NTP.

 "Each meter driver is a single opamp used to sum two signals, scale them and output the result to the meter. One signal is a voltage set between -12V and +12V (actually less because of the resistors on the high and low side of the adjustment potentiometer), and the other signal is an integrated voltage of one of the PWM outputs of the Arduino board. By loading a value between 0 and 255 in the Arduino’s PWM register for that channel, you output a DC voltage between 0V and 5V. The opamp sums these two voltages together and presents the voltage to the analog panel meter.

Using three PWM outputs from a microcontroller isn’t the ‘normal’ way to do a multichannel sample and hold. Normally, it would be built with a single sample and hold circuit, multiplexed with a computer controlled analog switch (like a 4066) to the proper meter. This way you would only need one PWM channel and two digital bits to control up to 4 meters, but since I was committing an entire Arduino to this project, it was just easier to build 3 sample and hold circuits using a single quad opamp, and a few passive components."