This circuit doubles the frequency of a rectangular signal applied to its input. The circuit has a 30 kHz input to obtain 60 kHz signals. We found it in a 1964 Electronic Design.
This Philips commercial circuit is from the 90's documentation. The integrated circuit must be...
We found this circuit in the September 1971 issue of Radio Electronics magazine. The sensor is an...
This circuit is from a Hands-On Electronics from 1987, but it can still be easily assembled, as...