As shown in the figure, it is the 555 fish tank water temperature automatic heating control circuit.
The water temperature automatic temperature control circuit comprises a step-down rectifier circuit, a wet control timing control circuit and a thyristor control circuit. When the temperature of the cylinder water is lower than 25 degrees, it is automatically heated and heated for 10 seconds to keep the water temperature at +25~30 degrees. The step-down rectifier circuit is composed of a step-down transformer T, a rectifier diode D1, D2, etc., and a voltage stabilizing circuit is composed of R4 and DW (2CW57), and the voltage of +9V is regulated.
IC1 (555) and RP1, RT, R1, R2, C1, etc. constitute a temperature-controlled single-temperature timing control circuit. RT is a temperature sensitive component that uses a negative temperature coefficient (NTC) glass-sealed thermistor; 555 operates in a monostable mode. Normally (temperature t<25 degrees) 555 is in the reset state, that is, the 3-pin output is low. When the water temperature in the cylinder drops, the resistance of the temperature-sensitive resistor RT in the water becomes larger, and RP1 is adjusted. When t=25 degrees, Make RP1+RT=2R1, when the water temperature is slightly lower than 25 degrees, there is RP1+RT>2R1, so that the trigger level of 555 is lower than the trigger flip level 1/3Vdd (3V), the 555 trigger is set, 3 feet The output is turned to a high potential, LED1 emits light, and the thyristor is triggered to conduct, and the resistance wire RL is energized and heated. The time of RL heating depends on the temporary stability duration of the 555 monostable circuit, that is, td=1.1R2C1.
The graphical parameters are designed for 10 seconds. When the stabilization time is up, the output of 555 turns to low level, LED1 goes out, SCR turns off, RL is powered off, and heating stops. When the water temperature drops to 25 degrees over a period of time, another temporary stabilization and heating process, so that the water is turned back and forth, keeping the water temperature in the cylinder above 25 degrees.
In the selection of components, the temperature sensitive resistor RT should choose the negative temperature coefficient (NTC) resistor, preferably the glass seal structure to prevent leakage, potentiometer RP1 can choose WSW organic solid potentiometer; heater is best used off-the-shelf The special heating device for the aquarium, the power should not be greater than 30W; the thyristor can be used with 1A and thyristor with a withstand voltage of not less than 400V, such as 3CTS1A-D type; the transformer T uses 5VA of the secondary coil center tap (10V). Pressure transformer.
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