Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the Sonalert type with included oscillator.
This circuit was obtained from ancient documentation using transistors of the time. The circuit...
I found this circuit in an old Argentine publication from 1973. The components are no longer...
This ammeter measures currents in 5 ranges from 50 uA to 0.5 A using a 40 uA instrument, which can be...