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AN3641

Low-Power, Cost-Efficient PIR Motion Detection Using the

tinyAVR® 2 Family

Features

• 12-bit ADC, Differential Measurement

• ADC Sample Accumulation Up To 1024 Samples

• Programmable Gain Amplifier (PGA) Up To 16x Gain

• Signal Amplifying, Oversampling And Analyzing Using The Built-in ADC With PGA

• Hardware Averaging Using Burst Mode

• ADC Triggered Through The Event System Using The Periodic Interrupt Timer (PIT)

• Reduced Bill Of Material (BoM) Cost Compared To Typical Passive InfraRed (PIR) Solutions

• Visualize Data Using The Microchip Data Visualizer And Data Streamer Protocol

• Visualize Power Consumption Using The Microchip Data Visualizer And a Power Debugger

Introduction

Author: Kjetil Kirkholt, Microchip Technology Inc.

This application note describes how to use the 12-bit differential ADC with PGA in the tinyAVR

® 2 Family of

microcontrollers and how to collect measurements using a sensor while keeping the currentPassive InfraRed (PIR)

consumption at a minimum.

In this application example, the signal from the PIR sensor is amplified, oversampled, digitally filtered, and analyzed

to determine if movement has occurred. LED0 on the ATtiny1627 Curiosity Nano (DM080104) board is used to

indicate when movement is detected. The measured data can be sent to the serial terminal and illustrated in the Data

Visualizer application or plugin for Atmel Studio.

The output signal levels from a PIR sensor are typically very low and less than 1 mV. To detect the movement and

avoid false detections, the signal needs to be amplified before being sampled by the ADC. In typical PIR solutions,

this is achieved by using several Operational Amplifier (op amp) stages with high gain. In this application example, no

external op amps are used, and the amplification of the signal is purely done inside the microcontroller (MCU) by

using the internal PGA. The ADC supports sampling in bursts, where a configurable number of conversion results are

accumulated automatically into a single ADC result (sample accumulation). The application example accumulates 16

samples, which increases the resolution of the 12-bit ADC by two bits. It is possible to oversample the signal up to

1024 times and gain five additional bits, resulting in a 17-bit ADC resolution, if needed.

More information on oversampling can be found in the ADC Oversampling with tinyAVR 0- and 1-series, and

megaAVR 0-series product brief.

For demonstration purposes, the ATtiny1627 Curiosity Nano board, Curiosity Nano Base for Click boards

™, and a

modified MIKROE-3339 PIR Click boards™ are used.

The example code for replicating the results described in this application note is available from Atmel START:

• PIR sensor with tinyAVR 2-series ADC

–start.atmel.com/#example/Atmel%3AApplication_AVR_Examples%3A1.0.0%3A%3AApplication

%3APIR_Motion_Detection%3A

The bare metal code example (without using Atmel START drivers) is available on GitHub:

View Code Examples on GitHub

Click to browse repositories

More information about the application is described in Sections and .Demo Operation Code Implementation

Additional details on the ADC performance and general configuration are available in the device data sheet.

AN3641

Table of Contents

Features......................................................................................................................................................... 1

Introduction.....................................................................................................................................................1

1. Block Diagram.........................................................................................................................................5

2. PIR Sensor Theory..................................................................................................................................6

3. Demo Operation......................................................................................................................................8

3.1. Configuring, Customizing, Tuning the PIR Application Sampling, Filtering and Detection

Parameters...................................................................................................................................8

3.1.1. Sample Acquisition Parameters.....................................................................................8

3.1.2. Filtering and Detection Algorithm Parameters...............................................................8

3.1.3. Debug Interface Parameters..........................................................................................9

3.2. Hardware Prerequisite..................................................................................................................9

3.2.1. Click board™ Modifications............................................................................................9

3.2.1.1. Filter Simulation Using MPLAB® Mindi™ Analog Simulator ......................11

3.3. Hardware Setup......................................................................................................................... 12

3.4. Software Prerequisite.................................................................................................................13

3.5. Running the Example.................................................................................................................13

4. Source Code Overview......................................................................................................................... 15

4.1. MCU and Peripheral Configuration............................................................................................ 15

4.2. Flow Chart..................................................................................................................................16

4.3. Timing Diagram.......................................................................................................................... 17

4.4. Code Implementation................................................................................................................. 17

4.4.1. Peripheral Initialization.................................................................................................17

4.4.2. Main Code................................................................................................................... 18

4.4.3. Warm-up and Filter Creation........................................................................................19

4.4.4. Update Average Filters................................................................................................ 20

4.4.5. Check for Movement....................................................................................................20

4.4.6. ADC Result Ready Interrupt Routine...........................................................................21

5. Summary...............................................................................................................................................22

6. Plotting Graph in .......................................................................................................... 23Data Visualizer

7. Plotting Power Consumption.................................................................................................................24

7.1. Power Consumption...................................................................................................................25

8. Get Code Examples from Atmel START............................................................................................... 27

9. Get Code Examples from GitHub..........................................................................................................28

10. Revision History.................................................................................................................................... 29

The Microchip Website.................................................................................................................................30

Product Change Notification Service............................................................................................................30

Customer Support........................................................................................................................................ 30

AN3641