This circuit digitally counts input pulses. The circuit from a November 1970 Radio Electronics uses unijunction programmable transistors. Note the counted pulse duration.
Found in an Electronics Now from the 90s, this circuit with the 555 generates a signal with 50%...
Frequencies from 1 to 10 MHz can be obtained with a small adjustment of the variable in a narrow...
This is a multi-component tester with visual indication by LED and polarity selection in the test....