Tropical fish tank water temperature automatic controller circuit diagram explanation_Air control circuit diagram explanation

　　The automatic water temperature controller for tropical fish tanks uses a negative temperature coefficient thermistor as a temperature sensing probe to automatically heat the fish tank through heating gas. The transient time of this circuit is small, which is beneficial to the accuracy of temperature control, and is suitable for fish tanks of various sizes.

　　Circuit working principle: After rectification by diodes VD2~VD5 and filtering by capacitor C2, a voltage of about 12V is provided to the control part of the circuit. The 555 time base circuit is connected as a monostable trigger, and the transient state is 11s. Assume the control temperature is 25°C, adjust the potentiometer RP so that RP+Rt=2R1, and Rt is the thermistor with a negative temperature coefficient. When the temperature is lower than 25°C, the Rt resistance increases, pin 2 of the 555 time base circuit is low level, then pin 3 changes from low level output to high level output, relay K conducts, and the contact absorbs Close, the heating tube begins to heat until the temperature returns to 25°C, the Rt resistance becomes smaller, pin 2 of the 555 time base circuit is at high level, pin 3 outputs low level, relay K loses power, and the contact is disconnected , heating stops.

　　Selection of components: IC uses NE555, μA555, SL555 and other time base integrated circuits; VD1 uses IN4148 silicon switching diodes; LEDs use ordinary light-emitting diodes; VD2~VD5 uses IN4001 silicon rectifier diodes; Rt uses 470ΩMF51 at room temperature Type negative temperature coefficient thermistor; RP uses WSW organic solid trimmer potentiometer; R1 and R2 use RXT-1/8W carbon film resistor; C1 and C3 use CD11-16V electrolytic capacitor; C2 uses CT1 ceramic dielectric Capacitor; K selects JZC-22F small medium power electromagnetic relay with working voltage of 12V.

　　Production and debugging method: The temperature sensing probe is connected to the thermistor Rt with plastic wires, and then the welding point and Rt are sealed together with epoxy resin glue, so that it is not afraid of water erosion. As long as the circuit is correct during the production process, this circuit is easy to implement. If the component performance is good, it can be used without debugging after installation.

　　Working principle of the circuit: This circuit is mainly composed of the sound-generating integrated circuit KD~9561 and the switching integrated circuit TWH8778. When working, the KD-9561 outputs the alarm signal, which is processed and amplified by the TWH8778 high-current switching integrated circuit to push the speaker to emit a loud alarm. Voice. The IC uses KD-9561 sound IC, or you can choose KD-9562 sound IC, and wire it according to the requirements to make it sound the alarm signal. IC2 uses the TWH8778 switching circuit. When the power supply voltage is 12V, the speaker BL should choose a speaker of 8Ω and above 3W or a special horn-type speaker. The resistance of the current limiting resistor R1 is 300Ω~510Ω. D2 uses a 3V voltage regulator tube. D1 is the circuit For protection diode, 1N4001 can be selected. After the circuit installation is completed, as long as the wiring is correct, it can generally be used normally without debugging.