Agricultural temperature control circuit

The 220v alternating current is transformed, rectified and filtered to obtain a 40V direct current voltage. Part of this voltage is sent to the detection
circuit, and the other part is separated into voltages of 12V, 16V, 28V, etc., which are used as
the power supply voltages of integrated circuits such as NE555, TDA2040, M51209, and HA17902 respectively.
    (1) Temperature control circuit In this circuit, the relationship between the thermistor RT (the resistance value RT of the thermistor at a certain temperature, material constant B, and absolute
temperature T is B=2.3[TIT2(T2- T1)log(Rlm/RRn)] is placed at the four corners, center or next to the door of the greenhouse. When the outside temperature
changes beyond the specified range, the RT resistance changes and the circuit operates to achieve temperature control.
    (2) Temperature measurement Circuit In the temperature detection circuit 1, the voltages taken from Ri05 are introduced into the comparators ICl-1 and ICl-2 respectively, and
compared with the standard voltage. In ICl-1, the reference voltage U=25.8V. When the temperature is lower than 30°C , ICl-1 outputs low level . When the temperature rises above 30℃
, then U-.->25.8v, Icl-l jumps and outputs high level. In ICl-2, the reference voltage U+ = 20V. When the temperature is higher than 15℃,
the comparator ICl-2 outputs a low level. When the temperature drops below 15℃, U-<20V, ICl-2 jumps and outputs a high level.
    Temperature detection The working principle of circuit 2 is the same as above, and the standard voltage value is shown in Figure 8-26.
    In the cooking and ventilation circuit, if the temperature is within the range of 20-25°C, the circuit will not work; when the temperature is lower or higher than When this specified value is reached
, the circuit operates. Adjusting RP501 can roughly adjust the heating jump temperature. The heating device can be a wall-mounted electric blanket or an electric stove, and the ventilation device can
be a ventilation fan.
    (3) Temperature alarm circuit The temperature alarm circuit is mainly composed of or It consists of three parts: gate circuit, oscillation circuit 2 and power amplifier circuit. Its working
principle is as follows: R40], R4.2, VD401, R403, R4.t, VD402, etc. form an OR gate circuit. VD403 stabilizes the voltage output by the OR gate. voltage.
When the temperature exceeds 30°C or is lower than 150°C, the temperature detection circuit outputs a jump signal to the OR gate circuit, and outputs a 12V voltage at point A.
This voltage charges G.z through RP401, ruler |.s, When the potential rises to 2/3 of Vc., the integrated block is reset, and pin ③ outputs low level. At the same time, the internal
discharge tube is connected to pin ①. The capacitor CioZ discharges to pin ⑦ through R406, and VC402 drops. When %.. drops. When it reaches 1/3 of vcr, pin ③ outputs
a high level, the discharge tube is cut off, and the discharge ends. Then it starts charging and discharging, forming an oscillation. The time required for discharge (low level) is 0. 7R406
C402. Required for charging The time (high level) is O+7(R406 +RRP401)C402. The period To．7(2R406_r-RRP4.1)A02. The ◎ pin outputs the high-level
duty cycle, which determines the tone of the speaker. TDA2040 has sufficient integrated power Amplifier. R412 and R411 constitute AC negative feedback, and C4 is the output
capacitor.