This circuit was found in the October 1989 issue of Radio Electronics magazine. It drives an auxiliary relay with the call signal for a possible louder bell.
August 2016 - Mouser Electronics is offering the development kit board Joule ™ 570x with expansion from...
In the figure we have a configuration that allows to test NPN transistors and with the addition of a...
This circuit was designed to work with the previous one in triggering a relay by the sounds picked up...