Timer for enlargers (CB8301E)

From the time when photographs developed on paper could be enlarged, this circuit was found in a 1960s General Electric documentation.

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Magnetic Alarm (CB16638E)
The sensors in this alarm are reed-switches. In the diagram we have only one, but several can be...
Who is the fast for 4 competitors (CB3859E)
We found this circuit in a Poptronics from 1998. The circuit can be extended to more competitors...
VCO With Operational (CB15466E)
The circuit shown in the figure uses two of the four operational amplifiers found on the LM324...