This circuit is from a 1964 Electronic Design. The sensor is an LDR and the transistors are general-purpose types. The circuit triggers when the light that falls on the sensor is cut off.
This circuit was found in an old publication from the 1970s. Despite using germanium transistors, it can...
The frequency of this oscillator depends on the coil and capacitors C1 and C2. For 1 MHz L1 is...
Found in an Elektor from the 90s, this circuit triggers a Sonalert-type buzzer when the sensor is...