Water temperature informing circuit based on 556 chip

Memory chip

As shown, the circuit consists of 556. The left part of the IC (1/2556) and the R1, R3, RP1 and thermistor probes form a one-shot. The thermistor is RT=3KΩ, with a negative temperature coefficient. When boiling water (about 100°C), the resistance is about 240Ω, and at 50°C, it is about 950Ω. If a certain temperature is preset, such as boiling water 100 ° C, RP1 is adjusted to 50 Ω, then VA = RT / (RP1 + R1 + RT) < 1/3, that is, when the trigger terminal 6 potential is lower than 1/3 VDD, trigger The device is set, the high level of the 5 pin output is added to the reset end of the right half 1/2556 (oscillator), then the start-up, f=1.44/(R4+2R5)C4, the oscillation frequency is about 1000Hz, telling the water Has been opened.