This document describes the concepts of movement detectors for noisy environments. The use of microcontrollers can improve the performance of traditional movement detectors.
This document is an application note titled 'Designing with Microcontrollers in Noisy Environments' (AN435/0894) from STMicroelectronics. It addresses the noise sensitivity and generation issues inherent in modern microcontrollers (MCUs), particularly in applications like power control and automotive use. The text explains that MCUs can lose control during disturbances or power glitches and can themselves generate interference due to high-speed switching transistors.
The note is divided into two main parts. The first part focuses on hardware solutions to increase equipment immunity, detailing optimized PCB layout techniques to minimize loop inductance and capacitance, and strategies for power supply filtering and decoupling. The second part discusses writing safer software to prevent control loss, specifically referencing the ST62 MCU family, and covers topics such as shielding, trace points, and program flow control.
| Inductivity ratio | around 10nH/cm2 |
|---|---|
| Decoupling capacitance range | 10mF to 100mF |
| High frequency decoupling range | 0.1mF to 1mF |
| Unused I/O pin impedance | 100kW |
The major noise receptors and generators are the tracks and wiring on the Printed Circuit Board (PCB), especially those near the MCU.
Inductance can be reduced by making the lengths and surfaces of the track smaller, such as placing track loops closer on the same PCB layer or on top of one another.
Recommended precepts include testing only clearly defined configurations, regularly checking vital data in RAM, controlling the program flow, and filling unused memory.