This telecommunications circuit was found in a National Semiconductor publication from the 90s. It is intended to convert the voltage from 48 V of telephone lines to 5 V with currents up to 1 A.
The sensors in this alarm are reed-switches. In the diagram we have only one, but several can be...
We found this circuit in a Poptronics from 1998. The circuit can be extended to more competitors...
The circuit shown in the figure uses two of the four operational amplifiers found on the LM324...