Found in an Electronics Now from the 90s, this circuit appears elsewhere in this section and website. The diodes are for general use and the basic frequency is given by C.
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...