This circuit that generates signals between 1.5 and 2 kHz was found in a documentation from the 90's. The capacitor C1 can be changed to obtain other frequencies.
We can implement this filter with more modern equivalent operational amplifiers, since the LM110 is...
This stethoscope or amplifier for hearing aid using a crystal headset and microphone was found in a...
The normal use of a 4520 as a divide-by-16 counter is shown in Figure bellow. In the normal...