555 new digital thermometer circuit diagram

As shown in the figure, the thermometer consists of a digital temperature sensor, a single stable circuit, a counting circuit, a decoding, a driver and an LED digital tube. The temperature measurement range is 0 ~ 50 degrees Celsius, the accuracy is 0.1 degrees Celsius, and the digital display is available. The wiring is simple and intuitive.

The temperature probe adopts SWC digital integrated temperature sensor AD 590 (or similar model). This device integrates a temperature sensing element and an analog-to-digital conversion (A/D), converts the temperature into a digital quantity, and expresses the measured temperature by the number of serial pulses. Each pulse is calibrated to represent a temperature increment of 0.1 degrees Celsius, then 0 to 50 degrees Celsius should correspond to the output of 0 to 500 pulses. Its conversion speed is less than 50ms, the power supply voltage is 12V and plus or minus 2V, and the output pulse frequency is 15kHz.

Based on the temperature measurement principle of the AD 590 temperature sensor, it is not difficult to design the circuit diagram of the thermometer . IC 1 (555), R2, C1, etc. form a monostable circuit, which generates a gate with a timing width of td=1.1R2C1, about 50ms, and adds it to the K pole of SWC and pins 10 and 12 of the counter. IC2 uses a 3-bit BCD code counter. After the output of IC1 is differentiated by C3 and R5, the positive pulse is used as the count clearing pulse of IC2. After a 50ms gate pulse is added to the K pole of the SWC, it starts. The output serial pulse is amplified by VT1 and then added to pin 11 of IC2 for counting. IC3 uses the BCD-seven-segment latch/decoder/driver CD4511 to decode the BCD code sent by IC2 and drive the common cathode seven-segment LED digital tube for dynamic display.

Figure b is the main waveform diagram of IC1 and IC 2.