This circuit is from American documentation from the 1980s. The transistors are general purpose types and the relay can be 6 or 12 V depending on the supply voltage.
This circuit was discovered in an English publication in 1979. The circuit can still be assembled with...
This circuit is the digital indicator for the previous circuit and can be used with similar...
This circuit tests crystals up to a few megahertz with ease. The circuit is from a 1977...