50 MHz Frequency-meter
The schematic below is that of a 50 MHz frequency-meter with digital display, made after a classic schematic, and uses exclusively TTL and CMOS ICs.
The frequency-meter can be used to directly measure quarz oscillators but it can also be used as logical probe at TTL level by uing the supplementary logical display (it displays “0” for zero logical level, “1” for 1 logical level and does not display anything is the probe is not connected.
The PDF schematic can be downloaded here.
Here you can download the schematic in Eagle format and here the board in the same format (new version using 74LS390).
Here you can download the schematic in Eagle format and here the board in the same format (old version using 74LS90).