A simple 555 timer Capacitive sensor switch can be designed using this circuit diagram. In this circuit, rectangular wave is integrated by triple RC network, while IC2, used as a comparator (with a baseline variable), use the integrated voltage changes to connect and disconnect AC relay. To decrease the risk of incorrect switching, with P1 and P2 is made fine and gross adjustment.
With this electronic circuit can monitor temperature in up to four points. Using this temperature monitor circuit can choose if the alarm should be triggered when temperature is increased or decreased. This depends on the resistance R10. If you connect R10 between positive supply conductor and output 6 of IC2 then circuit sound the alarm when the temperature rise over the reference temperature. The reference temperature is set by potentiometer P1. Measured temperature is monitored by NTC resistance R9.
A very simple 555 timer circuit Warning lights for bicycle with automatic disconnection can be designed using this circuit. This 555 timer circuit Warning lights for bicycle circuit will turn off warning lights of bicycle after about 3 minutes.