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TMP102 Temperature Sensor

Location

devices

Type

Implementation

Background

The Tmp102 utilizes I2C for communication and is capable of measuring temperatures ranging between -40˚C and +125˚C. A maximum of four sensors can be used simultaneously. The device’s serial bus address is configurable by connecting the address pin to one of four available connections.

The data-sheet for the device can be found here.

Overview

Communication with the device uses typical I2C. Temperature data is obtained in degrees Celsius and data bytes are transmitted with the most significant bytes first.

Detailed Design

API

namespace sjsu
{
class Tmp102 final : public TemperatureSensor
{
 public:
  struct DeviceAddress
  {
   public:
    static constexpr uint8_t kGround      = 0b100'1000;
    static constexpr uint8_t kVoltageHigh = 0b100'1001;
    static constexpr uint8_t kSda         = 0b100'1010;
    static constexpr uint8_t kScl         = 0b100'1011;
  };

  struct RegisterAddress
  {
   public:
    static constexpr uint8_t kTemperature   = 0x00;
    static constexpr uint8_t kConfiguration = 0x01;
  };

  static constexpr uint8_t kOneShotShutdownMode = 0x81;
  static constexpr std::chrono::milliseconds kConversionTimeout = 30ms;

  explicit constexpr Tmp102(
      sjsu::I2c & i2c,
      uint8_t device_address = sjsu::Tmp102::DeviceAddress::kGround);
  Status Initialize() const override;
  Status GetTemperature(
      units::temperature::celsius_t * temperature) const override;

 private:
  void OneShotShutdown() const;

  const sjsu::I2c & i2c_;
  const uint8_t kDeviceAddress;
};
}  // namespace sjsu

Device Address Configuration

The device address can be configured by connecting the address pin, A0, to either GND, V+, SDA, or SCL. This allows up to four Tmp102 devices to be used simultaneously.

Device Address A0 Pin Connection
0b100'1000 Ground
0b100'1001 V+
0b100'1010 SDA
0b100'1011 SCL

Table 1. List of available device addresses.

Initialization

explicit constexpr Tmp102(
    sjsu::I2c & i2c,
    uint8_t device_address = sjsu::Tmp102::DeviceAddress::kGround);
Constructs the driver object 
Status Initialize() const override
Initializes the I2c peripheral and returns the initialization status.

Obtaining Temperature Readings

The device is configured for one-shot shutdown mode when taking temperature readings to conserve power. That is, the device will take the temperature reading once and then shutdown until another reading is requested. Each reading requires a typical conversion time of 26µs.

static constexpr uint8_t kOneShotShutdownMode = 0x81;

void OneShotShutdown() const;
Writes the one-shot shutdown command to the configuration register to read the temperature once and then shutdown the device. The temperature reading can then be obtained from the temperature register.

Status GetTemperature(
    units::temperature::celsius_t * temperature) const override;
Returns the temperature reading in degrees Celsius.

Caveats

N/A

Future Advancements

N/A

Testing Plan

Unit Testing Scheme

An I2c driver shall be mocked and injected to the driver.

The following functions will be tested: - Initialize() - Should return Status::kSuccess. - GetTemperature() - The call count of the I2c method Transaction() should be exactly 2.

Demonstration Project

A demonstration project using the LPC17xx platform can be found here.