This circuit is one of many that the reader can find in this section for testing crystals. The circuit uses an indicator LED. Transistor Q1 determines the maximum crystal frequency that can be tested.
Found in a 90s nHands On Electronics, this circuit triggers a relay that shuts off the load when...
We found this circuit in an American 1980s documentation. The operational ones used are not common...
Found in a Popular Electronics from the 90s, this shield is activated by a 20 mA current. The...