Temperature measurement circuit

It is suitable for occasions with humidity restrictions. When the humidity exceeds the specified value, it will light up and alarm.
(1) Working principle The circuit structure is as shown in the figure, which is composed of humidity resistor R and 555 time base integrated circuit. When the humidity rises,
the resistance of the humidity-sensitive resistor R decreases, the AC voltage on the resistor increases, and
the DC voltage generated on the potentiometer RP after rectification by VD2 increases
. When the humidity rises above the limit value, the voltage of the trigger terminal ② and the threshold terminal ⑥ of the 555 time base circuit rises to 1/3 of the power supply voltage (i.e. V ratio/3), and its output terminal ③ output becomes Low level , the light-emitting diode LED lights up and alarms. At this time, dehumidification should be carried out. When the humidity is lower than a certain value, the resistance of R increases, and the voltage on Ri decreases. When the voltage of pins ② and ⑥ of the 555 time base circuit is lower than 1/6 of the battery voltage (i.e. Vcc/6), the output terminal ③The output of pin 3 becomes high level and the LED goes out. The external resistor R3 of the control terminal @ pin of the 555 time base circuit can change the input level threshold of the 555 , and reduce the voltage of the ⑤ pin to about 1/3 of its power supply voltage (i.e. v【.,/3). The DC power supply voltage of the 555 time base circuit is transformed from the mains through a transformer, VD1 is semi-rectified, and the capacitor C. Filtering and voltage stabilizing tube vs. provide voltage stabilization to about 7V.     (2) Component selection: 5G15 55, NE555, I.M555, etc. can be used for  the 555 time base circuit ; the humidity sensitive resistor can be plastic-encapsulated MS01-A or MS01-B (chip); the voltage regulator can be 2CW1 or 2CW12. The regulated voltage is required to be 7V, and the LED must use a transformer such as BT401 or other electric bell transformer. Requirement 2: The secondary side output is 6~10V and the current is more than 50rnA. If you make your own, you can use a 15mm thick GEl-12 silicon steel core. The primary side Use 4>0.08mm high-strength enameled wire to wind 5500 turns, and the secondary side to use @0.20mm enameled wire to wind 240-250 turns. Dip in varnish and dry.     (3) Installation and debugging: Purchase a printed circuit board, install the components, check the correctness based on the circuit schematic diagram, and then solder the welding surface. During debugging, when the relative humidity of the humidity-sensitive resistor R changes from 30% to 90%, its resistance will change from several thousand ohms to hundreds of ohms. When the humidity is at the upper limit, ten minutes after turning on the machine, adjust the potentiometer RP to the point where the resistance to the ground is maximum. At this time, the light-emitting diode LElD should light up to indicate, and then slowly adjust the center point downward until the The light-emitting diode I.ED just goes out, and the upper limit of the alarm humidity is set.     For the convenience of testing, the probe can be made into a probe form and then connected to the box of the alarm circuit with wires.