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  • Low Power Wireless PIR Motion Detector

  • Created: Oct 06, 2016

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High-end industries in the market uses motion detector or other sensing circuits to detect human presence or human interface. Adding wireless connection to these sensing circuits and detectors can save installation cost and can make the system flexible for future expansion by eliminating the presence of wires. The reference design is a low-power wireless PIR motion detector that uses CC1310F128RGZR, a member of the CC26xx and CC13xx family of cost-effective, ultra low power, 2.4-GHz and sub-1-GHz RF devices. For sensing human presence, the IRS-B210ST01-R1, which is a passive pyroelectric infrared sensor, was used in the circuit. Considering the low output of the sensor, LPV521 a single nanopower amplifier and TLV3691IDCKR a general-purpose comparator was used.

The reference design is powered by a coin cell battery (CR2032). Initially, the CC1310F128RGZR will wait in standby mode for two minutes to allow the PIR sensor and analog components to power ON. During this initialization, the output of both comparators should be 0V, else the CC1310F128RGZR will send an error signal and wait for the sensor to settle. The PIR sensors detect motion or movement of a body using the difference of temperature in which ambient temperature is the reference. The strength of this signal is proportional to the speed and distance of the object from the sensor that ranges from millivolts to few hundred microvolts peak-to-peak. Due to this low output, U1 and U2 with other external components form a fourth order bandpass filter using simple poles. Feedback diodes, D1 and D2 provide clamping so that the Op-Amps in both filter stages stay out of saturation for motion events, which are close to the sensor. Undesired signal is filtered in this stage. U3 and U4 form the window comparator of the circuit, which give a HIGH output when an input signal is between the range of PIR_OUT_HI and PIR_OUT_LOW. Together with U3 and U4, resistors R6 through R9, forming resistor divider, set up the thresholds that determine valid motion detection from the sensor. After receiving the signal output from the comparator, the CC1310F128RGZR will now transmit the signal to the end receiver.

The reference design can be featured in some other application like building automation, intrusion detection, occupancy detection, and powered battery systems. This reference design can also last for 10 years of operation.



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