This one-transistor alarm can be used with much more sensors than the two shown by the figure. Poser supply must be 2 V at least higher than the relay coil voltage to compensate voltage fall in the SCR.
This one-transistor alarm can be used with much more sensors than the two shown by the figure. Poser supply must be 2 V at least higher than the relay coil voltage to compensate voltage fall in the SCR.
