mcp9808 v0.1.0

MCP9808 high-accuracy I2C temperature sensor.

Application scenarios

• Board or enclosure temperature.
• A calibrated replacement for an NTC.
• Thermal logging near a power stage.

Contract

uint8_t mcp9808_init(mcp9808_t *device, mcp9808_port_t port, uint8_t i2c_address);
uint8_t mcp9808_read(mcp9808_t *device, int32_t *milli_celsius);

• init sets +-0.0625 degrees C resolution and continuous conversion.
• read returns millidegrees Celsius.
• Returns 1 on success, 0 on a bus error.

Parameters

• I2C address 0x18..0x1F.
• Resolution 0.0625 degrees C.
• The alert output is not exposed; use the threshold registers in an adapter.

Memory and timing

• 4 bytes; one 2-byte read.
• A conversion takes about 250 ms at the highest resolution.

Integration

mcp9808_t sensor;
mcp9808_init(&sensor, board_i2c_port(), 0x18);
int32_t temperature;
mcp9808_read(&sensor, &temperature);

Adapters

• The adapter issues a register write followed by a repeated-start read.
• Reference: LibDriver mcp9808 (MIT) and the Microchip MCP9808 datasheet.
• This implementation is original.

When not to use

• A remote probe several meters away; use a digital remote sensor.
• A fast control loop; the conversion time is too long.

Verification

make test covers positive, negative, and fractional temperatures.

void *context;
uint8_t (*write)(void *context, uint8_t address, uint8_t reg,
const uint8_t *data, uint16_t length);
uint8_t (*read)(void *context, uint8_t address, uint8_t reg,
uint8_t *data, uint16_t length);

mcp9808_port_t port;
uint8_t i2c_address;