This simple three-LED sensor uses an NTC at the input. The circuit is based on an uncommon integrated component today. We found it in documentation from the 80s.
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...