This circuit identifies the polarity of DC signals and if the signal is AC. The circuit is from 1969 US EDN documentation. Operational may be equivalent.
Found in the American 73 magazine for radio amateurs, this circuit can test common quartz...
This circuit for the automatic activation of a small lamp (or high brightness LED) was found in...
This circuit provides a 5 V negative output with a maximum current of 1 A. The circuit is from the...