Suggested by a Popular Electronics from the 90s, this circuit triggers an external load, relay or recorder, when the telephone line receives a call, thus enabling its recording.
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...