Tropical fish tank water temperature automatic controller circuit diagram

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℃, 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 is turned on, and the contact is closed , 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, the contacts are disconnected, and heating stop.

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 470Ω MF51 type negative temperature at normal temperature Coefficient thermistor; RP uses WSW organic solid trimmer potentiometer; R1 and R2 use RXT-1/8W carbon film resistors; C1 and C3 use CD11-16V electrolytic capacitors; C2 uses CT1 ceramic capacitors; K chooses JZC-22F small medium power electromagnetic relay with working voltage of 12V.