Thermostat control circuit made with NE555

This thermostatic controller has the characteristics of wide range of uses, 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 actuator. The circuit is shown in Figure 1. Rt1 and RP1 are the upper limit temperature detection resistors, and Rt2 and RP2 are the lower limit temperature detection resistors. When the temperature drops, when the potential of pin ② is lower than 1/3Vcc, pin ③ outputs high level, J pulls in, LED2 lights up, and heating begins. When the temperature rises and the potential of IC pin ⑥ is higher than 2/3Vcc, pin ③ outputs low level, J is released, disconnects the power supply of the controlled "electric heater" and stops heating. The component selection and production component list is shown in the table below. No. Name Model Quantity Rt1, Rt2 Thermistor 6.8K Negative temperature coefficient 2 RP1, RP2 Trim resistor 15K 2 R3, R4 Resistor 470Ω 2 C Polyester capacitor 0.01 1 LED One green and one red light emitting diode 2 IC Time base integrated circuit NE555 1 J Electromagnetic relay voltage 6V Current reference electric heater 1 When adjusting, the upper limit temperature should be adjusted first, and Rt1 should be placed in the required upper limit temperature environment (monitored with a thermometer). After one minute (Rt1 and the environment have reached thermal equilibrium), adjust Adjust RP1 several times until LED1 just lights up. You can first short-circuit pin ② to the ground to make pin ③ output high level (LED1 lights up), which makes it easier to observe the flipping status. Then adjust the lower limit temperature. The process is the same as above. Adjust RP2 to make red LED2 light up. Repeat the adjustment several times. You can first short-circuit pin ⑥ and power supply Vcc to make pin ③ output low level and observe the circuit flip state. It is best to use a small regulated power supply to power the circuit. With slight modifications, the circuit can be used as an over (high or low) temperature alarm.