8-Digit Frequency Meter

24 TEST AND MEASUREMENT 8-DIGIT FREQUENCY METER by T. Giffard A state-of-the-art frequency meter module is presented that has an 8-digit, 7-segment LED indication, a resolution of 10 Hz, and accepts input frequencies of up to 3.5 MHz. Its presetting facility makes this simple-to-build module ideal for incorporation in a radio receiver. The module is based on two ICM7217IPL CMOS presettable up /down counters. Two of these chips are cascaded to obtain an 8- digit read-out on common- anode 7-segment LED displays. The counter"s presetting facility makes it eminently suitable for use as a fre- quency read-out in recei- vers, since the intermediate frequency (e.g., 455 kHz or 9 MHz, can be programmed as an offset. In this manner, the output frequency of the local oscillator (L.O.) may be measured by the counter module, when driven by a suitable prescaler. Depend- ing on whether the L.O. fre- quency is lower or higher than the received frequency, the IF offset is divided by the prescale ...