This temperature control was found in General Electric documentation from the 90's. The circuit uses a 10k ohm NTC sensor as a sensor. The triac must be in accordance with the controlled load.
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...