This circuit was found in a PE Hobbyst Handbook of 1989. It uses a black light fluorescent of the time. Small fluorescent black light from 1 to 4 W can be used.
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...