Simple artificial intelligence temperature control circuit design

　　This paper introduces a temperature control circuit with simple artificial intelligence. When using this circuit for temperature control, you only need to turn the switch to position 2, set the control temperature, and use the temperature value displayed by the 3.5-digit digital display to accurately control the temperature, making the temperature control operation very convenient. LM35 is an integrated temperature sensor with calibrated internal circuit. Its output voltage is proportional to the Celsius temperature, with good linearity, high sensitivity and moderate accuracy. Its output sensitivity is 10.0MV/℃ and its accuracy is 0.5℃. Its measurement range is -55-150℃. The self-heating effect is low at static temperature. The working voltage is wide and can work normally within the supply voltage range of 4-20V. It consumes very little power and the working current is generally less than 60uA. The output impedance is low, which is 0.1Ω at 1MA load. According to the output characteristics of LM35, when the temperature changes between 0-150℃, the voltage corresponding to its output end is 0-150V. This voltage is divided by potentiometer W3 and sent to the detection signal input end of the 3.5-digit digital display head. When the voltage input at the input end is 150V, the displayed value is 150.0 by adjusting the potentiometer. After adjustment, the value displayed on the digital display head is the measured temperature value.

　　The temperature control selection can be realized through potentiometer W2. By adjusting W2, the voltage of the middle head can be changed within the range of 0-1.65V, and the corresponding control temperature range is 0-165℃, which can fully meet the general heating needs. When switch K is turned to position 2, the voltage of the middle head of potentiometer W2 is sent to the input end of the digital display head after passing through the voltage follower A to display the control temperature value. Adjust the potentiometer W2, and the value displayed by the digital display head will change accordingly. The displayed temperature value is the control temperature value. Potentiometer W1 is a pre-control temperature adjustment, and its voltage adjustment range is 0-0.27V, corresponding to an adjustable temperature range of 0-27℃. After this potentiometer is adjusted, the voltage of its middle head and the voltage of the middle head of potentiometer W2 are respectively sent to the inverting and non-inverting input ends of the comparison amplifier B, and the voltage at the output end of B is the difference between the two input voltages. This voltage corresponds to the difference between the two set temperature values. For example, adjusting W1 to 0.10V corresponds to a temperature of 10℃; adjusting W to 0.80V corresponds to a temperature of 80℃. The output voltage of B is 0.70V, indicating a temperature of 70°C. This voltage is sent to the voltage comparator C for voltage comparison with the voltage output by the integrated temperature sensor.

　　When the voltage output by LM35 is less than the output voltage of B, C outputs high voltage, and thyristor T1 is always turned on due to the bias current. AC 220V is directly applied to both ends of the electric heating element for high-power rapid heating. When the voltage output by LM35 is greater than the output voltage of B but less than the output voltage of A, it indicates that the actual temperature is close to the control temperature, C outputs low voltage, thyristor T1 is in the cut-off state due to no bias current, the voltage comparator D outputs high level, thyristor T2 is still in the on state, and AC 220V needs to be applied to both ends of the electric heating element through diode D2 for low-power slow heating (the heating power at this time is only 25% of the original). When the actual temperature rises above 80℃, the output voltage of LM35 is greater than 0.80V, the voltage comparator D outputs low level, thyristor T2 is also cut off, and the electric heating element is powered off.