This simple indicator circuit was found in a documentation from the 90s. Trimpots can have values between 2k and 10k, a series resistor is recommended to limit the current to the minimum setting.
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...