How to design ultra low power solution-part 3 Software Design

The design of IOT low-power equipment is roughly divided into three aspects: Device Selection, Circuit Design, Software Design and endurance life estimation——

Software Design
The software design is more reflected in how to drive the hardware into the low-power mode, such as: turn on the stop mode of MCU RTC wake-up; The EN pin of the control power supply enters the abnormal power supply mode; Analog input mode of GPIO; After sending the data, the communication module immediately closes the UDP connection to reduce the duration of high current mode as much as possible
Endurance life estimation

The static current can be measured with a multimeter (such as fluke’s 17b +). Because the sampling rate of the multimeter is low and the value presented is the effective value of measurement, for the dynamic current, such as the intermittent heartbeat packet current of the equipment, it is necessary to use an instrument with higher sampling rate, such as keysight’s n6705c; (for low-power measuring instruments, please refer to “talking about four low-power current testing” artifact “)

In the rigorous power consumption calculation, the self discharge rate of the battery should be considered, that is, even if the battery is not used, its own electrochemical substances will produce a certain reaction and consume themselves, especially the rechargeable nickel cadmium battery;

Give a simple example of life time calculation of low-power equipment:
Assuming that the battery capacity is 250mah and the heartbeat packet is sent once every 10 minutes to connect with the network, 30mA instantaneous current and 20ua standby current can be calculated as follows:
Power consumption of single docking network: 30mA x 5S = 150mas = 41.66uah;
Number of network connections in a day: (24h x 60) ÷ 10 = 144;
Total time of network connection in one day: 5S x 144 = 720s;
Total standby time of one day: (24h x 3600) s – 720s = 85680s = 23.8h;
Total power consumption in one day: (23.8h x 20ua) + (144 x 41.66uah) = 6475.04uah = 6.48mah;
Usable days: 250mah ÷ 6.48mah ≈ 39 days