This wired intercom circuit was found in an English publication from the 80's. The integrated circuit can be replaced by an equivalent, just like the transistor which is a general-purpose type.
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...