Infrared detector (CB7814E)

This circuit was found in a Popular Electronics of the 90s. The operational amplifier admits equivalent and the phototransistor can be of any type.

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Digital control with relays (CB23773E)
With the coded activation of the relays, it is possible to control which of the 16 outputs...
Programmable Current Shield (CB19955E)
The integrated circuit used in this application is not very common. Transistors and resistors...
Mains Voltage Indicator (CB11532E)
This simple circuit makes use of neon lamps to indicate the voltage of a power grid. The lamps are...