Introduction to high-precision and low-cost temperature measurement solutions

　　This article introduces a digital temperature sensor SD5075 with an I2C communication interface to achieve temperature measurement function. The software and hardware design schemes are described. The temperature resolution of the temperature measurement device is 0.1℃, and the typical error of the temperature measurement accuracy in the range of -40℃~+100℃ is less than ±0.5℃.

　　Measuring temperature with traditional mercury or alcohol thermometers not only takes a long time to measure, is inconvenient to read, and has a single function, which can no longer meet people's requirements in the digital age. This article proposes a design scheme for a new digital temperature measurement circuit. Hangzhou Jinghua Microelectronics Co., Ltd. has recently developed a high-precision digital temperature sensor chip SD5075, which is compatible with ADT75/LM75A/TMP75, has a lower price, higher accuracy, and good substitutability. This article will focus on it.

　　System composition:

　　The whole system consists of digital temperature sensor, single chip microcomputer, display, button and power supply. The circuit design is shown in the figure below:

　　

　　Circuit Diagram

　　SD5075 can set the hysteresis threshold register and the over-temperature threshold register. If the actual test environment temperature is higher than the set over-temperature threshold register, the alarm signal is output through the open-drain pin ALARM. If the actual environment temperature is lower than the hysteresis threshold register, the alarm signal is released. There are two optional working modes for the Alarm output: Alarm comparator mode and Alarm interrupt mode. The Alarm output can be selected to be high level or low level valid. For detailed operation procedures, please refer to the SD5075 single-bus digital temperature sensor specification on the SDIC official website.

　　SD5075 Introduction:

　　SD5075 is a high-accuracy temperature sensor chip with a high-precision temperature measurement ADC. The typical error is less than ±0.5℃ in the range of -40℃~ +100℃, and the typical error is less than ±1.0℃ in the range of -55℃~ +125℃. It is very convenient to establish communication with other devices through the two-wire I2C/SMBus interface. Setting the address lines A2 ~ A0 can support 8 chips in parallel bus connection.

　　This chip has three optional working modes: continuous temperature measurement mode, single temperature measurement mode, and shutdown mode. It can be flexibly selected and configured according to the requirements of speed or power consumption.

　　SD5075 Features:

　　1. 12-bit digital temperature reading with a resolution of 0.0625°C.

　　2. The maximum error is ±0.8℃ in the range of -40℃～+100℃, and the maximum error is ±1.5℃ in the range of -55℃～+125℃.

　　3. 2-wire communication interface, compatible with I2C/SMBUS protocol.

　　4. Provide over-temperature alarm function, and can set over-temperature threshold and hysteresis recovery threshold.

　　5. Continuous temperature measurement mode or single temperature measurement mode can be selected.

　　6. Low power consumption: The typical operating current is only 170uA during continuous temperature measurement, and the operating current in shutdown mode is less than 1uA.

　　7. Operating voltage range: 2.7V～5.5V.

　　8. Pin compatible with ADT75/LM75A/TMP75.

　　SD5075 pin description:

　　

　　Figure SD5075 pin diagram

　　SDA: two-wire communication data line

　　SCL: Two-wire communication clock line

　　ALARM: used for temperature alarm or SMBus Alert

　　GND: Ground

　　A2-A0: Address selection signal

　　VDD: Power supply

　　Microcontroller

　　The MCU model used is SD8102, which is also developed by Hangzhou Jinghua Microelectronics. It has 16k Bytes OTP space, 256 Bytes SRAM, 19 programmable I/O ports, 3 16-bit timers/counters, and a built-in 2M RC oscillator. This MCU can also be replaced by an ordinary 51 MCU or PIC MCU.

　　Display, buttons and power

　　It uses a 5-digit digital tube display, retains 1 decimal place, and uses dynamic scanning as the output mode. The 5 I/O ports of the microcontroller are selected as the bit lines of the digital tube and the 8 I/O ports are selected as the segment lines of the digital tube.

　　Press the S0 button to switch between Celsius and Fahrenheit.

　　An external power supply is used for power supply (no current limiting resistor is required for 5-12V, and a 470R/3W current limiting resistor is added when the voltage is greater than 12V), and the voltage is stepped down to 3.3 V by the HT7533 to power each module of the system.

　　software design

　　The microcontroller program flow is shown in the figure below:

　　

　　Program flow chart

　　Conclusion:

　　The SD5075 temperature measurement chip used in this temperature measurement solution has the advantages of low power consumption, high temperature measurement accuracy and low price, which is very suitable for ordinary temperature measurement occasions. It is also compatible with temperature measurement chips such as ADT75/LM75A/TMP75.