Darkness Monitor (CB21019E)

Found in Popular Electronics this circuit triggers an SCR and lights an LED when the location of the sensor is dark.

| Clique na imagem para ampliar |

Tunable notch filter (CB7404E)
We found this circuit in an English publication from the 1980s. The circuit uses current...
Telephone Relay (CB15524E)
The circuit shown in the figure can be useful in cases where a common telephone extension is used....
Proximity Switch (CB13489E)
We found this circuit in an American documentation from 1977. The circuit must not be powered by a...