How to minimize the power consumption of LoRa terminals? Reducing energy consumption has become an important issue for battery-powered products. The RNDU470T can reduce sleep energy consumption to the extreme, but how he achieved it, we will explain in detail.
Energy consumption is a major problem for battery-powered products. Once the power is exhausted, the device will “strike†and in some cases electrical energy means the life of the electronic product. In the Internet of Things era, more and more battery-powered devices will be connected via wireless communication, reducing energy consumption once again on the engineer's desktop—solving it.
The RMI terminal (referred to as the terminal) RNDU470T not only has the advantage of ultra-long-distance transmission of 5km in an open environment, but also reduces the sleep energy consumption to the extreme (0.4uA, with an RTC of 1.4uA). How did we do it? Next, decrypt step by step.
hardware design1. Use low power devices
The terminal MCU selects STM8L151C8T6, which belongs to ultra-low power consumption, 400nA without RTC sleep, and 1.4uA with RTC sleep. The MCU has a large RAM (4KB) and its own EEPROM (2KB), without the need to expand external storage devices, to reduce power consumption and cost in one step.
The terminal radio chip uses SX1278. In sleep mode, the power consumption of the chip is as low as negligible.
2. Let the RF module sleep as quickly as possible
The SX1278 is part of the LoRaTM spread-spectrum modulation technique, and its long-range advantage benefits from the modulation gain, not by increasing the transmit power (which would consume more power). The current consumption of the RF chip is as follows: sleep "0.2uA, idle = 1.6mA, receive = 12mA, transmit (maximum power) = 120mA.
The terminal MCU controls the SX1278 through the "interrupt + timer timeout" mode. Once the radio completes transmission or reception, it immediately enters sleep mode.
3. Understand the working mode and power consumption of the MCU
To reduce the power consumption of the MCU, first turn on the peripherals as little as possible, and then let them sleep as much as possible. Let's take a look at the power consumption of the STM8L151C8T6 in different operating modes.
The above low-power operation mode is a bit more for developers, especially the STM8L processor. We need general guidelines, and Table 2 below is the experience from practice.
4. Statically configure the MCU pin
Even if both the MCU and the RF enter sleep mode, they will “sneak†consume power if the MCU pins are not set. Take the STM8L151C8T6 as an example. It has a total of 48 pins. It needs to be classified by Excel first, as shown in the following example:
Generally speaking, the pins can be divided into five categories. You can use the "Metro Color Difference" method to design the following legend:
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