F-Logger: A frequency recorder


F-Logger is a frequency recorder. Its primary goal is to easily check the drift of a VFO over a long duration.
It is a variation of the well published PIC 16F84 frequency counters on the web like the "Weeder 50 MHz frequency counter", e.g. the variation made by Peter Cousins which you can find here. The display part was removed and every 1 or 10 seconds the measured frequency is send over a serial interface as comma separated values. The data can be captured with any terminal program, stored in a .CSV file, and displayed with a spreadsheet program. The serial interface runs at 9600 Baud, 1 stopbit, no parity.



The circuit is kept as simple as possible, a 16F629 is used to do the actual measurement. Although this counter is capable of counting up to 50 MHz, due to the 24 bit counter and 1 second gate time the maximum frequency is 16 MHz although this is can be easily modified. The RS232 signal conditioning is done via T1, any small signal PNP transistor will do. The RF signal is amplified with T1, use any fast RF transistor. Note that the R5/R6 ratio depends on the Hfe of the transistor (voltage feedback) so some fiddling may be required to set the proper offset. For sample selection the easeast way is to connect P1 to VCC via an 10k resistor and a switch to ground.



2005-10-24 - Initial breadboard experiments.
2005-10-25 - Completed


Frequency Logger assembler source
HEX file for 4 MHz crystal

questions or remarks can be mailed to PE1GRL