twin doorbell - with one push-button

with one push-button The present circuit is particularly useful where two families share one house, and where therefore two doorbells are a godsend, but where for one reason or another two push- buttons cannot be fitted. The only solution is then to operate the two bells with one push-button. When the button, Si, is pressed briefly, bell 1 sounds, and when it is pressed for a longer time, bell 2 will ring. Pressing the button triggers sequently the Q output, goes high. The Q output (pin 13) is applied to one of the inputs of AND gate Ni. The other input of N1 receives a high signal from IC4 (pin 3) and this lasts longer than the Q output of IC2. The output of N1 is then logic 1 which causes T2 to turn on and this results in triac Tril firing: bell 1 then rings. When the button, Si, is pressed for a longer time, it is still closed at the trailing edge of the output of IC1. Consequently, the D input of IC2 is low, and the Q output is high. This output is applied to one of the in- pu...