When it comes to searching for, or even sorting, the various quartz crystals at one’s disposal, it sometimes turns out that their markings are partially erased or even non-existent. The compact crystal tester described in this article can’t compete with more complex and expensive professional instruments, but it can be useful to check the correct functionality of an unknown quartz, displaying its frequency onto an eight-digit readout. With this crystal tester design, I wanted to create a simple yet sufficiently accurate device for my lab, mostly using standard components available in the drawers. There are of course other projects of this kind, but not with an 8-digit frequency display, as my prototype features in Figure 1. Figure 1: The eight-digit display prototype of the Crystal Tester at work, while testing a 30-MHz quartz. Crystal Tester Operating Principle As visible in the schematic of Figure 2, all the electronics revolve around a PIC16F876A micr...