Suggested by a Popular Electronics from the 90s, this circuit triggers an external load, relay or recorder, when the telephone line receives a call, thus enabling its recording.
This circuit is the transmitter for the previous project and also for what will come next. It is a...
In the figure we have an interesting configuration that allows, from a double T filter, to change...
This alarm circuit was found in a 1989 Poptronics, but all the components used are common, as the...