Found in American documentation from the 1980s, this circuit has a diode feedback. At the exit we have an indicator LED. The LM3900 is a transconductance operational amplifier.
This circuit uses a FET and a BJT to give a x300 gain for the input signal. So a 50 mV signal at...
This one-transistor alarm can be used with much more sensors than the two shown by the figure....
June 2017 - The new TE Connectivity FSJMI series of illuminated tactiles switches is now available in Mouser...