Based on the Linear Technology LTC2054, this -48 V circuit was found in a 2005 manual. The circuit is powered with 5 V and can be used as a shield.
This circuit was found in a 1980s US publication. It indicates when the phone is off-hook by...
This Radio Electronics circuit, in an 80's edition, decodes the 67 kHz signal used at the time to...
We found this circuit in an old American documentation. The table gives the values of the...