Low-noise and long-range passive infrared sensor conditioner circuit with MSP430 smart analog combo



Some MSP430™ microcontrollers (MCUs) contain configurable integrated signal chain elements such as op-amps, DACs and programmable gain stages. These elements make up a peripheral called the smart analog combo (SAC). For information on the different types of SACs and how to leverage their configurable analog signal chain capabilities, visit MSP430 MCUs smart analog combo training. To get started with your design, download the low-noise long-range PIR sensor conditioner circuit design files. This design leverages two of the four integrated op-amp blocks (SACs) in the MSP430FR2355 MCU. Two SAC_L3 peripherals are configured as cascaded op-amps in general-purpose mode to amplify and filter the signal from a passive infrared (PIR) sensor. The circuit includes multiple low-pass and high-pass filters to reduce noise at the output of the circuit to be able to detect motion at long distances and reduce false triggers. The output of the second-stage op-amp in this circuit can be internally or externally connected to other integrated peripherals in the MSP430FR2355 MCU. For example, the analog-to-digital converter (ADC) window comparator can sample this output periodically (with no CPU intervention) and trigger an interrupt when the signal crosses a threshold, indicating motion or an alert.
  • AC gain = 90 dB
  • Filter cut-off frequency:
    • fL = 0.7 Hz
    • fH = 10 Hz
  • Supply:
    • Vcc = 3.3 V
    • Vee = 0 V
MSP430 microcontrollers
MSP430FR2311 16-MHz integrated analog microcontroller with 3.75-KB FRAM, OpAmp, TIA, comparator w/DAC, 10-bit ADC MSP430FR2355 24-MHz 105-C integrated analog microcontroller with 32-KB FRAM, Op-Amps/PGAs, 12-bit DACs, 12-bit AD
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Technical documentation

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* Circuit design Low-noise long-range PIR sensor conditioner circuit MSP430 smart analog combo (Rev. A) PDF | HTML 06 Mar 2020
Application note How to Use the Smart Analog Combo in MSP430™ MCUs (Rev. A) PDF | HTML 24 Oct 2019

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