Create your own wireless motion sensor with

Transcription

1 Create your own wireless motion sensor with Arduino If you have a friend that has an alarm system in his or her home, I am sure you ve all seen these white motion sensors that are usually fixed above doors to detect anybody that would walk through the house when the alarm is on. They are usually the firs Written By: Feitan Page 1 of 17

2 INTRODUCTION In this article, we are going to see that you can reproduce exactly the same functionalities for a much lower cost, with any sensor you want, and of course using open-source hardware. Let s dive into the project! TOOLS: Arduino IDE (1) VirtualWire library (1) just place it in the libraries/ folder of your Arduino folder PARTS: Arduino UNO R3 board (1) Teensy board (1) RF link receiver & transmitter kit (1) PIR sensor (1) Breadboard and jumper wires (1) Page 2 of 17

3 Step 1 Create your own wireless motion sensor with Arduino There are two parts to build in this project: the receiver and the transmitter Receiver The receiver, the hub, is the simplest part to assemble. You need the big Arduino board, and the RF receiver module. On my module there were three pins: VCC, GND, and data. Simply connect the VCC pin the 5V pin of the Arduino board, the GND to the GND of the Arduino board, and the data pin to the pin number 11 of the Arduino board. Transmitter For the transmitter that is connected to the sensor, it is also quite simple. First, connect the transmitter. It also has three pins to connect: VCC, GND, and data. Simply connect the VCC pin the main power supply of the Arduino board you are using. Be careful, on the Teensy for example the main power supply of the chip is 3.3V. Then, connect the GND to the GND of the Arduino board, and the data pin to the pin number 12 of the Arduino board Page 3 of 17

4 Finally, connect the PIR sensor. It also has three pins like the radio module. Connect the VCC to the main power supply of your Arduino board. Step 2 Also be careful at this point: the PIR sensor I used could work without problems at 3.3V, but other requires 5V because of an on-board regulator, so you might have to do some soldering depending on your board and sensor combination. Please refer to the documentation of your PIR sensor to know which voltage you can use. Then, just connect the ground to the ground of the Arduino board, and the output pin to the pin number 7 of your Arduino board Page 4 of 17

5 Step 3 We will take care of the radio transmission in the last part of this tutorial, so for now, we will simply test the motion sensor. Most of the PIR sensors simply return a 1 when they detect motion, so on the Arduino it is easy to detect motion using: sensor_value = digitalread(sensor_pin); This is the sketch I used to test the sensor: const int sensor_pin = 7; void setup() { Serial.begin(9600); delay(1000);} void loop() { Page 5 of 17

6 Step 4 // Get sensor value sensor_value = digitalread(sensor_pin); // Print on serial Serial.println(sensor_value); delay(1000);} You can just upload this sketch, open the serial monitor and play with the sensor to check if it is working correctly. Step 5 Now that we made sure that the motion sensor is working, we can work on the radio transmission. Let s deal with the transmitter part first. As I said before, the key in this project is to use to VirtualWire library, or you will run into serious transmission troubles Page 6 of 17

7 For this reason, I will always use VirtualWire functions when transmitting or receiving data through the RF modules. As for many of my tutorials, I will first go through the important parts of the code, and then give you the full code for the project. It starts by including the VirtualWire library: #include <VirtualWire.h> In the setup function of the Arduino sketch, we have to initialize the transmission and set the transmission rate: vw_set_tx_pin(transmit_pin); vw_setup(2000); // Transmission rate The transmitter can sustain much more than 2000 bauds, but I want to be on the safe side here, and that s more than enough for our application. Then, we read the value of the PIR sensor with: sensor_value = digitalread(sensor_pin); Page 7 of 17

8 Step 6 We can then prepare the message that will be sent through the RF link, and change it if the sensor detected some motion: // Init message char msg[3] = {'o','f','f'}; // Change message if motion is detected if (sensor_value == 1){ msg[0] = 'o'; msg[1] = 'n'; msg[2] = '#';} Page 8 of 17

9 Step 7 Yes, I could have transmitted just 0 or 1 without any problem, but I wanted to see how reliable was the RF link to transmit some short words, this is why I decided to transmit on# or off. Finally, it s time to transmit the message every second (and flash the LED to indicate some transmission): // Transmit data every second digitalwrite(led_pin, HIGH); // Flash a light to show transmitting vw_send((uint8_t *)msg, 3); vw_wait_tx(); // Wait until the whole message is gone digitalwrite(led_pin, LOW); delay(1000); Page 9 of 17

10 Step 8 This is the complete transmitter code: // Include VirtualWire library #include <VirtualWire.h> // Define pins const int led_pin = 13; const int transmit_pin = 12; const int sensor_pin = 7; int sensor_value; Step 9 void setup(){ // Init vw_set_tx_pin(transmit_pin); vw_setup(2000); // Transmission rate pinmode(led_pin, OUTPUT); pinmode(sensor_pin,input);} void loop(){ // Get sensor value Page 10 of 17

11 Step 10 sensor_value = digitalread(sensor_pin); // Init message char msg[3] = {'o','f','f'}; // Change message if motion is detected if (sensor_value == 1){ msg[0] = 'o'; msg[1] = 'n'; msg[2] = '#';} Step 11 // Transmit data every second digitalwrite(led_pin, HIGH); // Flash a light to show transmitting vw_send((uint8_t *)msg, 3); vw_wait_tx(); // Wait until the whole message is gone digitalwrite(led_pin, LOW); delay(1000);} Page 11 of 17

12 Step 12 Now, the receiver. It is actually quite similar to the transmitter code. The setup is slightly different: // Initialise the IO and ISR vw_set_rx_pin(receive_pin); vw_setup(2000); // Transmission rate // Start the receiver PLL vw_rx_start(); In the loop of the Arduino sketch, we also have to create the buffer to receive the data: uint8_t buf[vw_max_message_len]; Step 13 uint8_t buflen = VW_MAX_MESSAGE_LEN; Then, we actually have to check if a message was received with: if (vw_get_message(buf, &buflen)) To finally print the message with: for (int i = 0; i < buflen; i++) { Serial.print(char(buf[i])); Serial.print(' ');} Page 12 of 17

13 Step 14 This last part will go through the received message and print every character, which should be on# or off in our case. This is the final receiver code: // Include VirtualWire library #include <VirtualWire.h> // Pins definition const int led_pin = 13; const int transmit_pin = 12; const int receive_pin = 11; void setup() { Step 15 // Init delay(1000); Serial.begin(9600); // Debugging only Serial.println("setup"); // Initialise the IO and ISR vw_set_rx_pin(receive_pin); vw_setup(2000); // Transmission rate // Start the receiver PLL Page 13 of 17

14 Step 16 vw_rx_start(); // Set LED pin pinmode(led_pin, OUTPUT);} void loop(){ uint8_t buf[vw_max_message_len]; uint8_t buflen = VW_MAX_MESSAGE_LEN; // Check if a message was received if (vw_get_message(buf, &buflen)){ Step 17 // Flash a light to show received good message digitalwrite(led_pin, HIGH); Serial.print("Got: "); // Print message for (int i = 0; i < buflen; i++){ Serial.print(char(buf[i])); Serial.print(' ');} Serial.println(); Page 14 of 17

15 Step 18 digitalwrite(led_pin, LOW);}} Page 15 of 17

16 Step 19 It is now time to test everything! The first thing to do is to upload the right sketch to the right board. It can be tricky if you have two boards connected to your computer at the same time, so this is what I did. First, connect the transmitter board to your computer and upload the transmitter sketch. Then, disconnect the USB cable, actually put all the transmitter part away from your computer (like in real situation, right?) and plug the Arduino board to an external power source (for the Uno board, between 7V and 12V. For other boards, refer to the documentation of your board). At this point, the LED of the board should blink every second to indicate that a message was transmitted. Then, connect the receiver board to your computer and upload the receiver sketch. You should immediately see the LED of the receiver board blinking to indicate that it received a message. Finally, open the serial monitor and you should see something similar to the picture Page 16 of 17

17 Step 20 From that point, there are many things you can do with this project. You can put the transmitter part wherever you want in your home (however, you might need to insert antennas on the RF module if you have a big home), and power the Arduino board with an external power source. Then, on the receiver side, you can for example implement an alarm mechanism that goes on when motion is detected. Or couple the project to the Arduino GSM shield to send you a SMS whenever something is detected. The possibilities are limitless, so experiment & have fun! This document was last generated on :32:35 AM Page 17 of 17