For the purpose to be used with QRP transceivers I have developed some frequency counters with different types of displays (from simple 8 LED display to 2 x 8 character LCD), but the f-counter described on this page I have found to be the most useful. The requirements I wanted to fulfil with this design, were:

After careful study of different types of solutions I have found out as the most appropriate solution to build the f-counter around a PIC16C71 microcontroller, mainly because of it's easy programming, low cost and on-board A/D converter.

The f-counter is built on two PCBs, one serves as a motherboard and the other as a display unit. To achieve small dimensions mostly SMT components are used.

As a display I have implemented two different solutions. First I tried the miniature Siemens DL340M four digit 7-segment LED unit with 2,5 mm digits (looks like LED displays, which have been used in calculators some 20 years ago, but is more up-todate). The advantage of it is simple PCB required and the drawback it's price (ca. 15 US$). So I developed also a display PCB for four HDN1077O (also Siemens) low currant 7-segment LED displays with 7 mm digits, which are also brighter at the same power consumption and have much bigger digits, although they occupy approximately the same space on PCB as DL340. As a display driver serves Motorola's MC14499P and to store the frequency offset a 93C46 EEPROM.