We found this circuit in December 1986, Radio Electronics magazine. It uses 3 inverters and has the frequency determined by the crystal. The power supply is 5 V.
We can use this circuit to connect low impedance microphones and even small speakers used as a...
This alarm circuit is from a 1987 publication, however the components used are still modern. The...
In the figure we have the way to implement a comparator for voltages of opposite polarities. The...