NE555 Temperature Controller

The constant temperature controller has the characteristics of wide application, high precision, low cost and easy installation and adjustment.

Working Principle
The thermostat controller consists of thermistors Rt1, Rt2, NE555 time base circuit, temperature range adjustment resistors RP1, RP2 and control actuators. The circuit is shown in Figure 1 (click here to download the schematic diagram). Rt1 and RP1 are upper limit temperature detection resistors, and Rt2 and RP2 are lower limit temperature detection resistors. When the temperature drops, when the potential of pin ② is lower than 1/3VCC, pin ③ outputs a high level, J is attracted, 1ED2 lights up, and heating begins. When the temperature rises and the potential of pin ⑥ of IC is higher than 2/3Vcc, pin ③ outputs a low level, J is released, and the power supply of the controlled "electric heater" is disconnected, and heating stops.

       
Component selection and production
component list are shown in the table below.
 

       
When adjusting, the upper limit temperature should be adjusted first, and Rt1 should be placed in the required upper limit temperature environment (monitored by a thermometer). After one minute (Rt1 reaches thermal equilibrium with the environment), adjust RP1 until 1ED1 just glows, and adjust it repeatedly several times. You can first short-circuit pin ② with the ground to make pin ③ output a high level (1ED1 is bright), so that it is easy to observe the flip state. Then adjust the lower limit temperature. The process is the same as above. Adjust RP2 to make red 1ED2 light up, and adjust it repeatedly several times. You can first short-circuit pin ⑥ with the power supply Vcc to make pin ③ output a low level and observe the circuit flip state.
The circuit is best powered by a small voltage-stabilized power supply (you can choose one in the power supply technology column of this site according to your actual situation).
This circuit can be used as an over (high or low) temperature alarm with a slight modification.