Svein
Vetti
Today, there are many applications
that require accurate and continuous temperature sensing to protect a product or
improve system performance. Temperature sensors now have the ability to deliver
accurate measurements wirelessly and in real-time thanks to advancements in
connectivity technology. In many applications, the ability to monitor and control a
system from a remote location is a key requirement. By combining long-range Sub-1
GHz networking with Bluetooth? low energy (2.4 GHz) connectivity opens up a
world of possibilities for temperature measurement. Here we will discuss how the use
of these technologies together can enhance systems where temperature measurement is
critical.
Some Example Applications - Cold Chain Management and Home Automation
Temperature sensing is used in many applications and below we will look at two examples:
- Cold chain management
- Home automation
Cold Chain Management
Cold chain
management is deployed to monitor and track products that are sensitive to
temperature. A typical example is fresh food being shipped from a farmer and tracked
all the way to the supermarket. The temperature of pallets or individual boxes is
monitored to ensure the quality of the produce. While monitoring solutions exist
today, the combination of Sub-1 GHz and Bluetooth low energy in a single device plus
a high quality temperature sensor enables new functionality. For example, the
long-range, Sub 1 GHz network enables coverage of a large area like a storage
facility and the Bluetooth connectivity enables an operator (truck driver, shop
assistant) to communicate directly with the pallet/box using a smartphone to check
if the product has been kept at the right temperature for the duration of its
journey. These technologies also allow a smartphone to be used as an Internet
gateway in places where a Sub 1 GHz network cannot be implemented – for example
during the truck transport. In this case the truck driver’s smartphone could be the
gateway without any intervention from the driver apart from running a smartphone app
in the background. This would allow remote systems to continue monitoring the
temperature of cargo.
Home Automation
Localized
temperature control is important for maintaining a pleasant indoor climate. By
wirelessly connecting sensors with ventilation/cooling/heating, it is also possible
to optimize comfort while at the same time making sure energy consumption is kept at
a minimum. Many home automation systems use Sub-1 GHz technology today for its long
range and low power consumption. In these solutions, temperature sensing is used in
heating, air-condition and ventilation systems (windows/blinds). At the same time,
Bluetooth connectivity allows users to access to the information via smartphones and
tablets. Using a single device for both connection methods, such as the SimpleLink? dual-band CC1350 wireless microcontroller
(MCU), allows for simple, cost-effective systems to be developed.
Building a Dual-band, Temperature Monitoring System
TI’s SimpleLink dual-band CC1350 wireless MCU is a new wireless system-on-chip
solution (SoC) that offers both the long range RF connectivity of the Sub-1 GHz frequency band, in addition to the simple connectivity of Bluetooth? low energy (2.4 GHz). The small size of the CC1350 solution and its low power
consumption make it ideal for building the systems described earlier. In addition, its interfaces allow for adding a temperature sensor directly without additional circuitry.
Figure 1 shows a block diagram of the CC1350 wireless MCU. For a digital
sensor like TMP18x (±0.3 degrees) single wire temperature sensor for in temperature
controlled vehicles, or TMP112 (±0.5 degrees), and TMP114 (±0.3 degrees) from TI, a
digital interface like the I2C or the SMBus? can be used for sensor
configuration and collecting temperature data. Assuming that the I2C is
used, there are two main ways of connecting the CC1350 wireless MCU to the
temperature sensor:
- Using the I2C interface that is directly controller by the ARM? Cortex?-M3 application processor. The I2C module has a dedicated driver library function that is integrated as a part of the TI RTOS (real-time operating system). The I2C software routine used to handle the sensor can be found here
on ti.com. This
can be used as an example to handle other I2C temperature sensors as well.
- Using the sensor controller on board the CC1350 device. The sensor controller has its own configuration tool called the Sensor Controller Studio that contains sample code for the I2C interface. To access this
code, download the Sensor Controller Studio and click on the I2C example on the front page.
Using the sensor controller will give the lowest current consumption. However, in most use cases, the temperature sensor is read out very infrequently (interval of ten seconds or more) – in these cases the difference with respect to average
current consumption is negligible between the ARM Cortex-M3 and the sensor controller. A temperature read of every 10s can easily be designed to consume less than 1μA in total current consumption – including the stand-by (32kHz) sleep
current consumption.
Connecting an Analog Temperature Sensor to a Dual-band Wireless MCU
Analog temperature sensors such as the LMT70 can be read by using the 12-bit
analog-to-digital converter (ADC) inside the CC1350 device. As for digital sensors, a user has a choice of using the TI RTOS that includes an ADC software driver run by the ARM Cortex-M3, or using the sensor controller. Examples of how to read out analog sensors can be found in the Sensor Controller Studio.
Figure 1 Block Diagram of the SimpleLink Dual-band CC1350 Wireless MCU