This is my gps display for the car- currently it uses a 16F628 running at 12MHz.
Update April 2016. Due to numerous h/d failures over the years, the source code for this project no longer exists, so with due apologies, custom changes are no longer possible.
Click here for the track layout, here for the component overlay,
here for the hex file for a 12 Mhz crystal and here for the hex file for a 10 Mhz crystal
The board is designed to solder directly to the connector on the rear of the display, but it is no problem to connect via a short cable if required. The contrast pot can be board-mounted or front panel, whatever suits, value is not critical, anywhere betwen 1 and 50k.
The board accepts standard NMEA data at 4800 baud, 8 bits, and no parity, so most gps's with a NMEA data output should drive it. The only problem would be if the data is inverted, in which case a simple single transistor inverter will cure the problem.
NOTE THAT THE NMEA DATA MUST BE AT TTL VOLTAGE LEVELS, RS232 VOLTAGES WILL KILL THE 16F628!!
Futurlec have the 4x20 displays in at a good price, likewise the 16F628.
A few interesting .pdf files I have come across to do with time & frequency
Fundamentals of Time and Frequency.pdf
Introduction to time and frequency metrology.pdf
Residual PM Noise Evaluation of Radio Frequency Mixers.pdf