Ble’s layered protocol stack can efficiently transmit a small amount of data with low power consumption, making it the preferred wireless protocol for battery powered applications, such as low-power sensor network interface that needs to extract and process data regularly. This paper will focus on how to effectively use ble to maintain low-power wireless operation in sensor applications with infrequent data changes.
At present, the world is entering an Internet of things (IOT) era in which various systems need to collect and exchange data. Ble plays an important role in the Internet of things in which sensors are connected wirelessly to form a network and realize data exchange between devices. The host device can be a smartphone that can monitor and control all network nodes. Such Internet of things (IOT) applications include daily activity tracking and home automation functions, such as efficient residential lighting, temperature and humidity monitoring and control, remote control of consumer electronic devices, etc.
If the sensor is battery powered, the power consumption is limited and must last for a long time, ble will be the best connection choice. For example, a low-power sensor for measuring temperature and humidity, whose parameters change slowly, can be connected to a ble integrated processor that can process and transmit data to the host device. The operational frequency of ble subsystem is not high, such as once every 100 milliseconds, and it is in low power consumption mode at other times. Ble devices such as cypress PSoC 4 ble can provide multi-user configurable power consumption mode, so as to optimize the operation of ble subsystem (bless) independent of processor working mode. It enables developers to reduce power consumption and make the service life of a single battery reach several years.
The five system power modes are active, sleep, deep sleep, sleep and stop modes. The three bliss power consumption modes are active, sleep and deep sleep. Bless mode is always enabled in deep sleep mode with a system power of 1.3 μ a. Ble subsystem can send and receive data in bless active mode. It can remain idle and remain connected in bless sleep mode and deep sleep mode. These power consumption modes are independent of the power consumption mode of the system, so developers can flexibly select the most efficient configuration for the system and bless respectively. On this basis, we can build a complete system with very low current demand and usually powered by button battery.
Sensors can be roughly divided into analog and digital. Typical analog sensors include sensors for monitoring smoke, gas, ambient light, personnel sensing, etc. Digital sensors include sensors that monitor temperature, humidity, pressure, acceleration, etc. When ble subsystem is integrated with application processor, sensors can be connected in many different ways. For example, an analog sensor may be fed to a SAR ADC with a voltage output at the front end. Digital sensors do not require analog conversion, so they can collect data through any communication interface (such as I2C, SPI or single line interface).
The integrated timer, counter, pulse width modulator and universal digital module (UDB) can be used to implement custom logic to further process sensor data. Finally, the processed or received digital data can be sent through the ble interface and monitored by the mobile phone with built-in ble function or any other client device. With the continuous change of resource availability and cost, different series of ble integrated processors (such as PSoC 4 ble) can be selected to adapt to various applications.
Wireless sensor networks are usually used as mesh networks and hub networks. The hub network includes all sensors that can be placed in the same location. Each sensor needs to be connected to a single ble peripheral (server) to process data and send it to the ble central device (client). Mesh network adopts a topology that can locate sensors remotely. Each node in the grid needs to be connected to ble peripherals (servers), and all these peripherals can be connected to ble central devices (clients).
The flexibility and rich resources of the built-in ble processor enable the sensor to connect to a single ble device. PSoC creator is an IDE for developing applications around the PSoC architecture. The figure shows the analog and digital sensor interfaces and ble subsystem. This configuration shows a typical industrial data monitoring system for sensing smoke, light intensity, temperature, humidity and pressure. Each component in the configuration has an associated application programming interface (API) that developers can access as needed. Each component also has a data table related to it, which describes the available configurations of the component.
Ble components are configured as slave devices in their gap layer. This allows any ble device (such as a ble mobile phone) to scan the device and be connected by the ble mobile phone when the ble slave device contains its name broadcast. In addition, in its GATT layer, ble devices are configured as GATT servers with custom profiles. The low power feature of ble is enabled in this component as discussed below. A single service called “sensor service” has five different features for collecting data from each sensor. Each feature has a notification function that can send sensor data as a notification.