SDG #08 Symmetricom GPSDO - Noritake VFD Interfacing - Part 2

Part two of the Symmetricom GPSDO project moves from teardown to actual firmware work, with the focus on getting a Noritake CU20025SCPB 2x20 character vacuum fluorescent display talking to a Microchip dsPIC30F3013. The toolchain is MPLAB X paired with an MPLAB Real ICE for in-circuit debugging, which matters here because character display initialisation is one of those tasks where a single mistimed strobe or a missed busy-flag check leaves you staring at a blank panel with no clue why.

The Noritake module is a useful choice for instrument front panels. It uses a broadly HD44780-compatible command set, so existing character LCD experience transfers over, but the VFD gives far better contrast and viewing angle than a typical STN LCD and needs no backlight. Brightness is software controllable, which is worth planning for early if the finished unit will sit on a bench in a dim lab. The trade-off is higher current draw and a display technology that ages, so it is worth considering whether the panel will be lit continuously.

Alongside the display work, the GPSDO’s own PCB gets a closer look to find a practical tap point for the OCXO’s 10MHz output. That is the real prize with surplus telecom timing hardware: a disciplined oscillator locked to GPS makes an excellent house frequency reference for calibrating counters, scopes and signal generators, at a fraction of the cost of a purpose-built lab standard.

The end goal is a front panel showing time of day and date, driven directly by the microcontroller rather than a canned display module, which keeps the door open for status indication and menu features later.