"Wireless sensor nodes can reduce implementation costs by reducing sensor size, simplifying maintenance issues, and extending battery life. In fact, if we focus on the design without battery, we can achieve greater cost-effectiveness.
The best way to design battery free devices is to reduce the average power consumption of wireless sensor systems through technologies such as low-power Bluetooth (ble) for communication and energy acquisition.
Figure 1 shows the architecture of micro wireless sensor. The sensor is created using a microcontroller (MCU) with integrated ble RF, which can operate completely using the power supply provided by the energy acquisition power management integrated circuit (IC).
[figure 1 | the micro wireless sensor is created using a microcontroller (MCU) with integrated ble RF. After optimization, it only operates with the power supply provided by the energy acquisition power management IC. The figure shows the complete wireless sensor - cyalkit-e02 solar powered ble sensor reference design kit (RDK).]
Ble optimization
In order to operate only with the power supply provided by the energy acquisition IC, the sensor must optimize its ble system to reduce power consumption. First, the designer must understand the details of ble subsystem. Next, you need to write firmware code to meet the requirements of each operation / power mode. Then, designers must analyze the actual power consumption to confirm various assumptions to further improve the energy efficiency of the system.
Refer to cypress cyalkit-e02 solar powered ble sensor reference design kit (RDK) for the description of power reduction technology. The RDK includes a cypress PSoC 4 ble and s6ae10xa energy acquisition power management IC (PMIC).
The simple and power free ble design should first configure the ble RF as a beacon in non connectable broadcast mode. Ble beacon is a one-way communication method that broadcasts outward every certain time. It contains some smaller packets (30 bytes), which constitute a broadcast packet and are sent out. If the beacon is found, it can push messages, APP operations and tips in various smart phones or computer applications.
Figure 2 shows the ble link layer format of broadcast channel packet format. Ble link layer has "preamble", "access address", "protocol data unit (PDU)" and "cyclic redundancy code (CRC)". Please note that the following information only applies to the broadcast channel packet format and does not include "data channel packet".
"Preamble" must be set to "10101010b"
"Access address" must be set to "10001110100010011011111010110b (0x8e89bed6)"
"PDU" includes "header" and "payload"
The packet structure of ble beacon belongs to "broadcast data" in "payload".
[figure 2 - ble link layer format of broadcast channel packet format]
[figure 3 | ble beacon packet format]
Table 1 lists the settings.
Table 1: < ble beacon Format >
− Length1 0x02
− AD type1 0x01
− AD data 0x04
− Length2 0x1A
− AD type2 0xFF
− Company ID 0x0131 [Cypress Semiconductor Corporation]
− Device type 0x02
− Length3 0x15
− UUID1 00050001-0000-1000-8000-00805F9B0131 [hex]
− Major2 Your own ID
− Minor3 0x0001
− RSSI4 0xC3 [-61dBm]
− Transmitter power 0 dBm
− Advertise interval 1500 ms
1 this is a 16 byte string used to distinguish a large group of related beacons.
2 this is a 2-byte string used to distinguish group beacons in larger packets.
3 this is a 2-byte string used to identify each beacon.
4 received signal strength indication. Used to determine the distance of the beacon.
The average consumed current can be calculated using voltage and current waveforms to determine the efficiency of ble design. Figure 4 shows the power consumption results of no power optimization design.
[figure 4 | current consumption of ble design without power optimization]
The average current is about 5 mA, and the total power consumption from start to standby is 34.76 MJ. In order to operate with ambient energy, we need to reduce the current consumption.
Low power consumption by optimizing firmware
Reduce the average current consumption of ble design by optimizing the following four functions:
1. Low power start
2. Deep sleep
3. IMO clock setting
4. Commissioning selection
When the system is in low power consumption mode, the watchdog timer (WDT) needs to be used to wake up the system.
Low power start
After power on reset (POR), ble system initializes these components by calling the startup functions of different components. During initialization, low-power operation is realized by performing the following steps:
1. When the 32.768-khz watch crystal oscillator (WCO) is started, turn off the 24 MHz external crystal oscillator (ECO) to reduce power consumption.
After 2.500 MS (WCO startup time), enable WDT to wake up the system.
3. Configure MCU to be in deep sleep mode within 500 ms WCO startup time.
4. After WCO is enabled, restart eco to enable ble subsystem (bless) interface.
5. Place WCO in low power consumption mode and change the low frequency clock (lfclk) source from 32 ‐ kHz internal low speed oscillator (ILO) to WCO.
6. Enable WDT to wake up the system.
7. Put MCU into deep sleep mode.
[figure 5 | low power start waveform]
Deep sleep
The user design shall manage the system clock, system power mode and bless power mode to realize the low-power operation of ble MCU.
During the ble event interval, it is recommended to achieve deep sleep by performing the following steps:
1. Turn off eco to reduce power consumption.
After 2.1.5s (ble event interval), enable WDT to wake up the system.
3. Put MCU into deep sleep mode.
After 4.1.5s, restart eco to enable ble subsystem (bless) interface.
5. Send ble broadcast data.
6. Repeat from step 1.
[figure 6 | deep sleep waveform]
IMO clock setting
The 3-MHz to 48 MHz internal main oscillator (IMO) is the main internal clock source. The default frequency of IMO is 48 MHz, which can be adjusted in steps of 1 MHz in the range of 3 MHz to 48 MHz. Under the default calibration setting, the tolerance between IMO and RDK in this example is ± 2%. Figure 7 shows an example of the total power consumption after changing the IMO frequency.
[figure 7 | IMO DC specification and example total power consumption]
Debugging selection
The serial line debug (SWD) pin is used for runtime firmware debugging in the development phase. Configuring the SWD pin to debug mode increases current consumption. Therefore, these pins should be switched to general input output (GPIO) mode at the final version so that they can still be used for device programming when the chip is reset.
We can use voltage and current waveforms to calculate the average consumption current of ble design to confirm the optimization degree of design. Figure 8 shows the power consumption results of the power optimization design.
[figure 8 | current consumption of power optimized ble design]
The average current is about 1.5 µ a, and the total power consumption from start to standby is 0.106 MJ.
Run with energy acquisition technology
At this average current and total power consumption level, it is necessary to confirm that the system can operate with energy acquisition technology. Figure 9 shows a block diagram of the energy acquisition system. The system adopts s6ae10xa energy harvesting (EH) PMIC series, and can run all day with cyalkit-e04, s6ae102a, s6ae103a evk and cy8ckit-042-ble ble pioneer kit.
[figure 9 | block diagram of energy acquisition system]
The block diagram in Figure 10 shows the energy acquisition process of PSoC 4 ble based on s6ae102a and s6ae103apsoc circuit boards.
WAVE1 shows the ble operation based on solar energy, and WAVE2 shows the ble current consumption during transmission. The PMIC first stores solar energy into a 300 on vstore1 (vst1)- μ F on ceramic capacitor. When vst1 reaches vvouth, energy is sent to MCU for ble operation.
[figure 10 | simple energy acquisition]
However, this simple energy acquisition process cannot run continuously for a whole day without backup capacitors (for example, during periods without light).
The block diagram and waveform in FIG. 11 show the hybrid energy storage control function. The energy used to operate the system is stored in vst1, and the remaining energy is used to charge vstore2 (vst2). When there is no ambient light, vst2 can continuously provide energy for the system.
[figure 11 | mixed energy storage control function]
The waveform in FIG. 12 shows the charging curve when energy is stored in vstore2. S6ae10xa stores energy in vstore1 (small capacitor) and vstore2 (large capacitor). The energy stored in vstore1 is used for system operation, and the remaining energy is used for charging the sub energy storage device of vstore2 (vst2). Vstore2 continuously provides energy to the system, so the system can continue to operate for a period of time even without ambient light.
[Fig. 12 waveform for storing excess energy]
The block diagram in Figure 13 shows the hybrid power input control mode. WAVE1 shows how the PMIC controls two power sources (solar and battery). PMIC drives the system in different scenarios by converting the two power supplies. Ambient light is usually continuous, but there may be no continuous light in some places. PMIC can automatically switch the two power supplies and continue to supply power without light.
[figure 13 | hybrid power input control]
S6ae10xa automatically changes the power supply according to the voltage of vstore1. If the voltage of vsotre1 reaches vvoutl, it will be powered from Vbat power supply to continue power supply without ambient light.
The following are examples of how to implement different applications.
[Figure 14 | compact solar wireless sensor that needs to run all day]
[figure 15 | compact solar door sensor requiring short-time / frequent operation]
[figure 16 | solar passive infrared sensor]
Original link: https://www.eeboard.com/news/taiyangneng-5/
Search aiban.com and pay more attention. You can master the latest development board, intelligent hardware, open source hardware, activities and other information every day. Recommend attention!
[wechat scanning can be followed directly]
Technology knew:
With the support of 15 development platforms, a thousand sets of free board lineups and a 10000 yuan cash award waiting for you, the Qunying solicitation order of 2017 MAOZe electronic intelligent manufacturing innovation competition has begun. Do you dare to accept the order?
Why is ZTE inferior to Huawei in mobile phone business? Because a good hand has already been played badly!
Because we can see through the development of smart speakers in the next few years, an intelligent speech recognition development kit will break the blood of giants!
Qualcomm connects Huawei Qilin 970: who can't build Ai unit modules into the chip
China's new supercomputing completely bid farewell to imported CPUs, and domestic chips ft-2000 series have been enough to compete with foreign countries“
Our other product:
