TMP117 Driver 'Lite' - Example

Purpose of this example is to demonstrate the use of the TMP117 driver 'Lite' in a (multi-)sensor application.

The TMP117 driver is a compact, powerful, light-weight and power-efficient software library for the Texas Instruments TMP117 high-accuracy, low-power, digital temperature sensor with I²C interface.

The TMP117 Driver 'Lite' provides basic functionality for temperature measurements at minimum power consumption. TMP117 Lite is inspired by Nils Minor's TMP117-Arduino.

TMP117 'Lite' Features

• Uses shutdown mode to minimize power consumption (250nA)
• Supports Power-On Reset configuration, eliminating MCU/I²C initialization overhead;
• Interrupt-driven sensor data handling through Data Ready callback;
• Provides 16-bit actual, lowest and highest temperature data with a resolution of 7.8125 m°C per increment
• Temperature data available after a One-Shot conversion:
  • Actual temperature
  • Lowest / Highest temperature(s), when changed
• Capturing lowest 'ever' and highest 'ever' temperatures in the device's EEPROM
• Error feedback after EEPROM write failure

Example Program

The example uses delay loops instead of (HW) timers and sleep mode. Using timers and sleep mode are highly recommended to take advantage of the low-power capabilities of TMP117 Lite.

Hardware used for this example:

• BlueDot TMP117 sensor board (comes with on-board 4.7k pullups on all signal pins)
• SODAQ SFF dev board (SAMD21G18 MCU with ARM M0+)

Signal wiring between BlueDot and SODAQ board:

• BlueDot TMP117 I2C <==> SODAQ SDA/SCL
• BlueDot TMP117 Alert ---> SODAQ A11

Initialization

Two initialization functions are available:

  <sensor>.initSetup(
                TMP117_mod mode,
                TMP117_avg averaging,
                const bool save_min_max_in_eeprom,
                uint8_t sensor_id
                )

  <sensor>.init(
                const bool save_min_max_in_eeprom,
                uint8_t sensor_id
                )

function / parameter	description
initSetup()	perform SW setup of TMP117 using mode and averaging values
init()	use Power-Up Reset configuration stored in EEPROM, no CPU/I2C overhead
mode	recommended mode: TMP117::shutdown
averaging	recommended value: TMP117::avg8
save_min_max_in_eeprom	(setting for <sensor>.readSensor())
	0: do not update lowest/highest temperatures in EEPROM
	1: update lowest/highest temperatures in EEPROM, when changed > 0.047°C
sensor_id	assign id to sensor (0-31)

Power-On Reset Programming

The TMP117 has the ability to store a Power-Up Reset (POR) setting in its EEPROM. This POR value is loaded into the configuration register during the TMP117 power-up cycle and does not require initialization by software.
To program a POR configuration, initialize TMP117 with the desired setting and store this in EEPROM:

  // Set TMP117 to shutdown-and-avg8 mode, do not write lo/hi temperature to EEPROM, sensor ID = 0
  <sensor>.initSetup(TMP117::shutdown, TMP117::avg8, 0, 0)

  // write TMP117 configuration to EEPROM, reset lo/hi EEPROM registers to factory values
  // returns true on failure, false if ok
  <sensor>.initPowerUpSettings()                  

When done, change this to:

  // use POR initialization only (mode/averaging are ignored), no EEPROM updates of lo/hi temperature, sensor ID = 0
  <sensor>.init(0, 0)

POR programming using the Example program:

1. In tmp117_example.cpp, make sure setupDone is set to false and build, load and run tmp117_example
2. Program prints out the lowest/highest temperature values before they are reset and stops after programming the EEPROM ("... Program ends here...").
3. Change the value of setupDone to true and build, load and run the example again. The TMP117 uses the stored POR configuration setting - no SW initialization required.

Capturing Lowest/Highest Temperatures

Driver initialization:

  <sensor>.init(1, 0) // enable writing lowest/highest temperature to EEPROM
  //            |  |
  //            |  +-- sensor ID
  //            +-- enable write lo/hi temp to EEPROM

The driver keeps track of the lowest and highest temperatures. It also stores these values in TMP117 EEPROM when save_min_max_in_eeprom is 1 and values have changed at least 0.047°C (to limit the number of EEPROM writes). This feature can be used to capture the lowest and highest temperatures over a longer measurement period without requiring any external data logging.

Before enabeling EEPROM writes, make sure the lowest/highest EEPROM values are reset to their factory values.
A reset is done by <sensor>.initPowerUpSettings() (above). After a reset, make sure no temperature readings are taken until the device is at the intended measurement location, to avoid incorrect lowest/highest values being stored in EEPROM.