Build Your Own Tuning Fork Clock!
Kris Slyka has created an ATtiny4313-powered tuning fork clock to replace the mechanical timepiece on his desk.
Inspired by Wilco Lunenburg's Tuning Fork Clock, Kris Slyka made a similar device with some hardware upgrades. The motivation to build the tuning fork clock was to replace the loud mechanical clock on the desk.
For those unfamiliar with the concept, a tuning fork clock counts the cycle of the tuning fork to keep time. The original clock by Wilco used an "optical sensor to measure the vibrations of the fork and an electromagnet to keep it going." However, Slyka wanted to find a more efficient and symmetrical way to do this.
The idea was to use the inductors for driving and sensing coils. Since the tuning fork does not have its own magnetic field, the clock employs a neodymium magnet to generate an external field. For this to work, the designed circuit amplifies the output of the sense coil and minimizes the harmonics.
"This circuit is surprisingly effective and can sustain the oscillation of the fork down to less than three volts while drawing around 1mA," Slyka notes. "When running at 5V, like in the finished clock, it's also sensitive enough to be self-starting, eliminating the need to tap the fork to get the clock going."
The digital section of the clock has an ATtiny4313 MCU and a 74HC595 shift register. "The ATtiny4313 uses one of its timers to count the oscillations of the tuning fork and handles serial I/O and a push-button rotary encoder for user input. The 74HC595 is used to shift out the data to be displayed on the five multiplexed seven-segment displays," Slyka adds.
The firmware is written in C language that can set the time and fine tuning of the clock speed. For more details on the firmware, it's all open source via GitHub. You can now develop your own tuning circuit as Slyka has provided all the circuit diagrams and PCB files.