SLAAE30 July   2021 MSP430FR2355

 

  1.   Abstract
  2.   Trademarks
  3. 1PIR Design Description
    1. 1.1 PIR Sensor
    2. 1.2 PIR Signal Chain
      1. 1.2.1 Traditional Motion Detection Signal Chain Design
      2. 1.2.2 Capacitor-Free Signal Chain Design
  4. 2Software
    1. 2.1 Software Architecture
    2. 2.2 Software Flow Chart
    3. 2.3 Power Profile
    4. 2.4 Data Processing
      1. 2.4.1 Digital Signal Conditioning
      2. 2.4.2 Low-Pass Filter for Temperature Drift
      3. 2.4.3 Spikes and Noise
      4. 2.4.4 Motion Detection Function
  5. 3Hardware and Schematic
    1. 3.1 MSP430FR2355
    2. 3.2 Schematic
  6. 4Results
    1. 4.1 Distance: 15 ft (4.5 m)
    2. 4.2 Distance: 22.5 ft (6.9 m)
    3. 4.3 Distance: 36.5 ft (11.1 m)
  7. 5Summary
  8. 6References

2.3 Power Profile

The software flow is also what controls the system's power profile. The first current spike is where the MSP430 wakes to enable the analog circuits, then goes back to sleep while the reference voltages are stabilizing. After a short period of time, the MSP430 wakes back up to check the Vref reference voltage and that the SACs are ready. Two ADC measurements are made from each stage of the signal chain. Finally, there is some data processing on the new samples to determine if there was motion before the MSP430 shuts down the analog circuitry and returns back to sleep where the system it spends 99% of it's time.

This software flow gives us an average current of approximately 6 µA with a 20 sps measurement rate.

GUID-B4B29F6C-9969-4578-8130-CEF00BF8D8AB-low.png Figure 2-3 Power Profile of MSP430 PIR Demo Software