set your clock to perfect time

The black box is a device that clock collectors and clock repair people can use to measure the beat of mechanical clocks and watches. The display shows the beat (left and right side), the number of beats averaged, and the average beat to a precision of one hundred millionth of a second. A microcomputer in the circuit allows the timing measurement to be calibrated by one-second pulses from a GPS signal to an accuracy of better than 100 nanoseconds. I had not used software for circuit layout before, so I needed some help at first using the PCB123 tools, especially for the dense wiring around the surface mounted microcomputer. After making a couple calls to Sunstone customer service, though, I found using the PCB123 design software as much fun as a video game! The precision placement in PCB123 allowed me to place drill holes not only for mounting the display, but also for using the pc board as a drill template for cutting out the display window and for locating the holes for the switches and jacks in the control panel. The hardest part was soldering in the microcomputer by hand. All 48 pins had to be lined up on the pc board and each pin had to be solidly connected without bridging to the other pins. Even though I had to clean off and resolder the pins several times to get it right, none of the pads on the Sunstone pc board came off or showed any signs of being disturbed. I added some test points for the microcomputer so that I can use this project to test other ideas using the display before laying out a new circuit. My thanks to Sunstone for providing the free PCB123 tool for garage workbench circuit designers like myself and for the fast delivery on low-priced, high quality pc boards!

- Shared November 21, 2012