A Frequency Counter

From July 1999 to September 1999 I constructed and documented a frequency
counter of the year 1999. I've taken a picture of this device:

The Frequency Counter from the year 1999.

You can connect a microphone to the front of the frequency counter. There is also a terminal
at the rear part of the device, if you want to measure an electric signal. At first step this signal is
connected to the little black box that is on the frequency counter. The circuit of the little box is
a signal divider. Of course the output of signal devider is connected to the frequency counter.

Some data
Frequency range:  1-39,999 Hz
Peak value of input signal:  5 mV
Input resistance of microphone terminal:  10 kohms
Input resistance of rear terminal:  100 ohms
Main supply:  AC 230 V, 50 Hz, 33 VA

When you're fetching a video for the first time, there's some loading time and
the screen is black.

Video: Measuring 50 Hz   1 min., 23.1 MB
Video: Measuring 440 Hz   30 s, 15.1 MB
Video: Measuring 1 kHz   20 s, 9.0 MB

My Device Story