PIR sensor power requirements.Human Body Sensor Vendor

　　During the operating life of the system, the MSP430F2003 MCU operates at less than 1? A's low-power mode allows long-term power supply with a single CR2032 3V button battery. The system uses a built-in internal low-frequency oscillator as the clock of the timer, starting a new transition every 340ms. A sampling rate of about three samples per second may sound slow, but since the sensor output changes very slowly in human sympathetic applications, such a low sampling rate is sufficient for reliable movement detection. Using a fast-starting high-frequency internal clock source (frequency set at 1MHz) to drive the AD converter results in a conversion time of 1.024 ms per sampling. From a low power perspective, it is important to keep the conversion time as short as possible because the internal reference voltage and the AD converter consume more than 70% of the total consumption.

　　In order to get a clearer impression of the current consumption of the system, the following table details the operating current and average current of each part of the system.

　　The total system current will depend on the final scheme of the system. It can be seen from this table that the consumption of the operating state mainly depends on the reference voltage and the current converted by AD, while the average consumption mainly depends on the sensor current. Because of the long turn-on adjustment time (several seconds or more) of PIR325 sensors, the method of Power cycling cannot be adopted for the sensors. Although the sensor must remain continuously switched on, current consumption remains low. With the hardware design and software process presented here, the total average current can be achieved below 10? A's universal mobile detection system. With a standard 3V CR2032 battery, it can work for more than two years.

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