This blog is the sequel of blog “Bluetooth technology”. In the previous blog “Bluetooth Technology” we discussed in detail about the basics of Bluetooth, how communication takes place and how are they classified. In this blog, we will describe in detail about various parameters and options that are available in each while designing a Bluetooth Low Energy (BLE) based IoT device.
Today we find numerous BLE enabled IoT devices emerging in market with typical applications such as wrist wearable in healthcare, Beacons & tags in retail and many more in home automation, industrial, automotives etc. In all these domain applications, most important criteria’s while designing the device are as follows
- Form factor
- Sensor integration
- User interface
- Power supply
In the following sections we will discuss in detail what are all important for selecting a BLE SoC in building a BLE based IoT devices and multiple options that are available to choose from.
BLE SoC is an integrated chip that includes both the Microcontroller and BLE transceiver. They are also named as wireless microcontrollers. The microcontroller part includes the core, flash memory, RAM and peripherals such as GPIO, I2C, SPI, UART, timers, ADC, etc. BLE part includes RF transceiver compatible with BLE specifications (usually v4.0, v4.1 or v4.2). In addition to BLE, some of the SoC also supports IEEE 802.15.4 standard compliance which is a standard that defines the operation of low-rate wireless personal area networks (LR-WPAN). It is the basis for the ZigBee, MiWi, Thread etc.
Following are the selection criteria for BLE SoC,
- Core: Most of the BLE SoC in the market is powered by ARM Cortex core such as Cortex-M0+, Cortex-M3 etc. There are few SoC with 8051 core also. The choice of the core depends on the nature of the application, where M3 will be a better choice for high computational performance, real time applications and M0+ for low cost yet better performance applications.
- Memory: All the SoC will have on-chip SRAM and Flash memory, where the size of the flash memory is of more concern which will be loaded with the application, OTA code and BLE stack. Hence selecting SoC with sufficient flash memory will be advisable. In some cases the application code and BLE stack itself will accommodate the full flash memory and there will be no more memory to support OTA. In such case, there is no other option than going for external EEPROM which adds some cents to dollars in the BoM.
- TX/RX Power: For any BLE based wireless application, range will be an important factor. The power of the transceiver is the main factor deciding the range. The transceiver power will be specified in dBm. More the dBm, better is the range. The range factor will also depend on the type of antenna used in the design and the same will be discussed in the upcoming section.
- Power: Mostimportantof all criteria is the power consumption. Both MCU and RF transceiver power consumption should be taken into account while selecting the SoC. BLE TX/RX and core/peripheral power are the major power consuming sections. During selection of SoC, the most important points to be taken in to account with respect to power consumption is as follows
- Option for controlling the TX/RX power: Power consumption due to TX/RX can be controlled by varying the TX/RX power. Less the TX/RX power, lower is the power consumption but it has considerable impacts on range as well.
- Option for multiple low power operating modes: Low power modes are the operating modes where some of the peripherals, clocks, etc in the MCU are disabled for low power operation. By selecting appropriate low power mode based to the application, the power consumption can be reduced.
- Peripherals: The core section of the BLE SoC includes multiple peripherals such as I2C, SPI, I2S, GPIOs, Timers, UART, ADCs, etc. BLE SoC under consideration should have multiple options to support external interfaces such as sensors, actuators, displays, audio visual indications, etc. For example, a fitness tracker is a BLE based wearable device that requires multiple digital sensors to acquire the real time data from the body such as MEMS sensors like accelerometer, gyroscope, magnetometer etc and such sensors provide digital data that can be acquired by interfacing with the BLE SoC through I2C and SPI. For analog sensor based applications the analog signals from the analog front end circuits can be acquired using the high resolution ADC available in the SoC. Some devices may require audio notifications such as buzzers which can be driven by the PWM signals available in the timers.
- Package: BLE SoC’s are available in SMD packages such as QFN and BGA. Among them QFN package is most common. The soldering process recommended for both packages by the chip vendors will be machine soldering which adds extra assembly costs.
- Operating conditions: The operating grade is a very important during the selection of SoC. The designed must careful in selecting the domain where the device is going to be used such as industrial, automotive, commercial or medical. For example, a commercial grade SoC is not suitable for automotive grade applications.
- Availability of the evaluation platforms, source code and stack ups should be verified which can support rapid product development.
Following are the popular BLE SoC part numbers available in the market from various semiconductor manufacturers,
- Texas Instruments: CC2540, CC2541, CC2640, CC2650
- NXP Semiconductors: KW30Z/31Z, KW40Z/41Z
- Renesas: RL78/G1D
- Nordic: nRF52840, nRF52832, nRF51822, nRF51824, nRF51422
- STMicroelectronics: BlueNRG-1
In addition to the SoC, for a device design that require only BLE connectivity, there are various modules available. These modules will include the SoC with inbuilt chip or PCB antenna. All the necessary peripherals will be brought to the expansion connectors and the power can be fed through the same. The communication with the BLE module will be an I2C/SPI/UART interface. The main advantage of those BLE modules is that, they are fully tested and compliance certified.
Embien Technologies is a leading provider of embedded design services for the Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully executed many projects like based on IoT such as healthcare Wearables, Gateways, and Data Analytics etc. Embien also offers a set of wearable design collections complete with electronics, firmware and Cloud that can be used to shorten product development costs and time significantly.