JEDEC JC 42.4 compliant Temperature Sensor

Overview

This sample application periodically (0.5 Hz) measures the ambient temperature. The result is written to the console.

If triggered measurements are enabled the sample initializes and maintains a ±2° C window around the current temperature. When the temperature moves outside the window an alert is given, and the window is moved to center on the new temperature.

Requirements

The sample requires a JEDEC JC 42.4 compliant temperature sensor. The sample is configured to use the MCP9808 sensor.

The MCP9808 digital temperature sensor converts temperatures between -20° C and +100° C to a digital word with ±0.5° C (max.) accuracy. It is I2C compatible and supports up to 16 devices on the bus.

Wiring

The MCP9808, which is a JEDEC JC 42.4 compliant temperature sensor, is available in a discrete component form but it is much easier to use it mounted on a breakout board. We used the Adafruit MCP9808 Sensor breakout board.

Building and Running

After providing a devicetree overlay that specifies the sensor I2C bus and alert GPIO, build this sample app using:

# From the root of the zephyr repository
west build -b particle_xenon samples/sensor/jc42
west flash

Sample Output

Note that in the capture below output from the trigger callback and the main thread are interleaved.

*** Booting Zephyr OS build zephyr-v2.1.0-537-gbbdeaa1ae5bb  ***
Alert on temp outside [24500, 25500] milli-Celsius
Trtrigger fired 1, temp 15.9375 C
iggAlert on temp outside [15437, 16437] milli-Celsius
er set got 0
0:00:00.017: 15.9375 C
0:00:02.020: 16 C
0:00:04.022: 16.125 C
0:00:06.024: 16.1875 C
trigger fired 2, temp 16.3125 C
Alert on temp outside [15812, 16812] milli-Celsius
0:00:08.027: 16.3125 C
0:00:10.029: 16.375 C
0:00:12.032: 16.5 C
0:00:14.034: 16.5625 C
0:00:16.037: 16.5625 C
0:00:18.039: 16.625 C
0:00:20.042: 16.6875 C
trigger fired 3, temp 16.8125 C
Alert on temp outside [16312, 17312] milli-Celsius
0:00:22.044: 16.8125 C
0:00:24.047: 16.875 C