This 4-tube counter was found in Radio Electronics magazine from December 1959. The circuit uses a coil as a sensor to detect the passage of metallic parts or magnets.
We found this circuit in a 1982 documentation. An intercom to be good must be sensitive and have...
With an optical coupler and a power transistor, which can be the BD135, it is possible to control...
The Variable Frequency Oscillator (VFO) shown in the figure can generate signals in a frequency range...