This is what my ardPET does. It’s a precision event timer implemented on an Arduino. Several advantages over a picPET and a few disadvantages, but:
- runs on Nano, Uno, Leonardo, microPro and Mega2560
- Programmed in C using the Arduino-IDE, source code here
- serial interface on USB
- 2 to 4 PETS available per chip
- other functionality can be added – the PET function can be a sub-part of a larger project.
Like picPET, accuracy and precision depend only on the quality of the resonator, several options available. In the example below I cut the nasty ceramic resonator off the board and wired a 20MHz TCXO instead. It provides twice the resolution of a 10MHz picPET. (Thanks again to the forum friend who sent me the TCXO!)
A bog-standard Leonardo gives reasonable results because it’s resonator is a quartz crystal, if that’s “good enough”.

The main advantage of ardPET is it can be extended. Though I recommend it highly, picPET is only a Precision Event Timer, with limitations such as no USB! My experimental clock, based on a Nano, implements two PETs. One measures the actual frequency of the Arduino’s oscillator relative to a GPS second, AND uses the second PET to measure a pendulum’s period relative to the Arduino’s GPS calibrated resonator. The Nano also detects beam break AND impulses the pendulum AND displays date-time AND reads temperature, pressure and humidity AND logs everything to a PC. A Mega2560 can support up to 4 PETs. Main disadvantages are Arduino modules being more expensive than picPET, and the owner has to operate the IDE. Of course picPET costs rise if a pic-programmer has to be bought, perhaps £20, and that has a learning curve too. Also, picPET requires a 10MHz oscillator, so some additional electronics needed – not difficult.
Dave