This alarm siren circuit has a latch. We found it in an article in the January 1975 Radio Electronics magazine. Note the power given by Rx and the speaker. It can be increased by changing Q1.
This circuit controls two relays from a single temperature sensor. The first fires when the...
This integrated amplifier was found in an English magazine that no longer exists, from 1975. The...
In the figure we have the way of obtaining 220 V from two equal 110 V transformers or 230 V from...