The circuit is small regulatorof temperature, us warns for the increase of temperature. The control of temperature becomes from the thermistor TH1, that is negative factor. His resistance is altered between in the 10K in temperature 25° C and roughly in the 1K in their 94° C. The trimmer TR1 regulates the precise temperature in which the Q1-2, connected as darlington, conduct, making him relay K1 close also the buzzer BZ, sound. The alarm is activated when the temperature becomes bigger than predetermining. The thermistor it should he is placed far from the remainder circuit, in order that this is not in danger from the temperature.
The supply of circuit becomes from battery 9V, but if he is placed in constant place, then we can him supply with one power supply . In the contacts of relay we can connect what load we want, as a lamb, other circuit k.a. Also can is added a LED, if we want to have also optical clue of excitation. The regulation becomes sinking him thermistor TH1, in water which we know the temperature of (the contacts should are well insulate so that do not have short-circuit) and regulating him trimmer, until excited the circuit. The cable that we connect the circuit with the TH1, should be plate.
R1= 820 ohm D1= 5.6V 0.5W Zener K1= 6V 200 ohm Relay
R2-3= 1Kohm D2-3= 1N4148 BZ1= Buzzer
C1= 220uF 16V Q1-2= BC550C S1= 1x2 Switch
TR1= 2.2Kohm Trimmer TH1= Thermistor 10Kohm at 25° C BATT= Battery 9V or external supply