Found in an old Popular Electronics, this circuit warns when a remote lighting system is not working. The circuit uses an LDR as a sensor and the components used are quite common today.
This General Electric circuit is from the 80's. The PUTs used in this meter are not common...
This circuit uses a transistor as noise source and a 741 IC as amplifier, sourcing a high...
In the figure we have a practical circuit for a 50 kHz bandwidth amplifier using a photo diode as...