This article introduces a digital temperature sensor SD5075 with I2C communication interface to achieve temperature measurement. The software and hardware design scheme is described. The temperature resolution of the temperature measuring device is 0.1 °C, and the typical temperature error is less than ±0.5 °C in the range of -40 °C to +100 °C.

Measuring temperature with a traditional mercury or alcohol thermometer not only measures long time, inconvenient readings, but also has a single function, which cannot meet the requirements of people in the digital age. This paper presents a new design scheme for digital temperature measurement circuits. A company has developed a high-precision digital temperature sensor chip SD5075, which is compatible with ADT75/LM75A/TMP75, and has lower price, higher precision and better substitutability. This article will focus on this.

[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:

The SD5075 sets the hysteresis threshold register and the overtemperature 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. The actual ambient temperature is lower than the hysteresis threshold register to cancel the alarm signal. The Alarm output has two selectable operating modes: Alarm Comparator Mode and Alarm Interrupt Mode. The Alarm output can be selected to be active high or low. For detailed operation procedures, refer to the SD5075 single-bus digital temperature sensor specification on the SDIC official website.

Introduction to SD5075:

SD5075 is a high-accuracy temperature sensor chip with high-precision temperature measurement ADC. The typical error is less than ±0.5°C in the range of -40°C to +100°C, and the typical error is less than ± in the range of -55°C to +125°C. 1.0 ° C. The two-wire I2C/SMBus interface makes it easy to establish communication with other devices. Set the address lines of A2 ~ A0 to support 8 chip parallel bus connections.

Typical application block diagram of SD5075:

SD5075 typical application block diagram

The chip can be selected in three working modes: continuous temperature measurement mode, single temperature measurement mode, and shutdown mode. Flexible choice and configuration based on speed or power consumption requirements.

SD5075 features:

1, 12-digit temperature reading with a resolution of 0.0625 °C.

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

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

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

5. Optional continuous temperature measurement mode or single temperature measurement mode.

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

7, working voltage range: 2.7V ~ 5.5V.

8, the pin is compatible with ADT75/LM75A/TMP75.

SDA: two-wire communication data line

SCL: two-wire communication clock line

ALARM: for temperature alarm or SMBus Alert

GND: ground

A2-A0: Address selection signal

VDD: power supply

Single chip microcomputer

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

Display, buttons and power

It adopts 5-digit digital tube display, retains 1 decimal place, and the output mode adopts dynamic scanning mode. The 5 I/O ports of the single-chip microcomputer are selected as the bit line of the digital tube and 8 I/O ports as the segment lines of the digital tube;

Use the S0 button to switch between Celsius and Fahrenheit.

Power is supplied by external power supply (5~12V does not need to add current limiting resistor, add 470R/3W current limiting resistor when it is greater than 12V), and the HT7533 is stepped down to 3.3V to supply power to each module of the system.

【software design】

The process of the microcontroller program is referred to the following figure:

MCU program flow


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

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