Since many of our readers will not be familiar with the 50MHz Frequency Meter presented in the October 2003 issue, we are presenting the design in full. No doubt kitset suppliers will bring out the updated version of the kit but many readers will want to update a kit they have already built. This is easy to do because there are only a few circuit and hardware changes and the PC board itself is unchanged.

As far as the circuit is concerned, the major change is in the PIC microcontroller. We have used a PIC16F628A instead of the originally specified PIC16F84P, because we needed a larger memory. Other changes include an LM2940CT-5 low dropout regulator instead of the 78L05, an additional toggle switch on the front panel and the aforementioned internal battery pack. In other respects, the circuit is unchanged.

Frequency meters are used in virtually all areas of electronics and are invaluable for servicing and diagnostics. Among other things, they are ideal for checking the operation of oscillators, counters and signal generators. This unit is auto-ranging and displays the frequency in Hz, kHz or MHz.

This makes it easy to read, as it automatically selects the correct range for any frequency between 0.1Hz and 50MHz and inserts the decimal point in the correct place for each reading.