Arduino Shock/Vibration Detector Project

The first two blocks of code are simply for defining important input & output pins and variables. This includes digital pin 2 (D2) for the HW-513 shock/vibration sensor, in addition to pins D3 & D4 for the red and green pins on the HW-480 2-colour LED module, respectively. In addition, a boolean variable called ‘val’ is declared that stores the digital output signal (HIGH/LOW signal) that the Arduino receives from the HW-513 sensor module. Several integer and long variables are also defined for the storage of number values, and these variables will become clearer as we look at other parts of the code.

Moving onto the void setup section, we set both LED pins as output devices and our sensor pin as an input device since digital information from the sensor is being fed into the Arduino. This is done via digitalWrite() functions. Next, serial communication is set up by setting our baud rate to 9600 bauds.

The last line of the void setup section features a special function, attachInterrupt(). Interrupts are very unique functions that can be used when dealing with timing issues. In this case, since the shock/vibration sensor is constantly feeding back information to the Arduino at a very high rate of speed, we can use an interrupt to ensure that the moment a shock/vibration is detected, it is processed by the Arduino correctly. Using an interrupt helps the microcontroller to detect these small input changes from the sensor while performing some other work also. One of the reasons why digital pin 2 (D2) was used for the HW-513 sensor was specifically due to digital pins 2 and 3 having interrupt capabilities (pins with interrupt capabilities do vary from Arduino board models). More specifically, digital pin 2 corresponds to digital pin 0 as the interrupt pin and that is the reason why a ‘0’ is seen within the argument of the attachInterrupt() function. The next part of the argument is to define when the interrupt occurs, also known as the interrupt service routine (ISR). In this code, we added another void section, called void shakeInterrupt(), to define the parameters of the ISR. If we scroll down to the bottom of the code, where the ISR we set points us to, we basically want the interrupt to set the variable ‘val’ to 0. With the function millis(), we start a stopwatch counting up the time from when the code is first running and this data is stored in the starttimer variable (as declared in the earlier sections of the code). This information will be important later. Moreover, moving back up to the original function, the last part of the argument defines the mode, or when the interrupt should be triggered. In our case, it is set to FALLING, meaning that the interrupt will trigger whenever the interrupt pin (D0 which is connected to D2) goes from high to low, or when the sensor detects a vibration to when the sensor is still.

For the void loop section, we first introduce an if-else statement which states that when the sensor returns a HIGH value (i.e. when a vibration is detected), the green LED is switched on and the red LED is switched off. This may seem counterintuitive to its working function as when the vibration sensor is shaken, a red LED is displayed, but this is all due to the presence of the interrupt function as mentioned above. Moving on, we add one to the value of the integer variable ‘loopcounter’ as defined in the early sections of the code. The purpose of ‘loopcounter’ is now revealed as the following if statement states that when the value of ‘loopcounter’ equals 3000, the digital input value of the HW-513 sensor is printed to the serial monitor and the variable ‘loopcounter’ is reset back to 0 for it to count back up again. The reason for this if statement is to ensure that the vibration sensor sends an accurate reading back to the Arduino based on a certain number of HIGH or LOW signals it receives. We definitely don’t want the vibration sensor triggering and sending back a HIGH signal due to a single faulty reading (outlier). 

At this point, we have covered the first half of the if-else statement but there is still the ‘else’ half that will now be explained. If the digital input signal from the sensor is LOW (i.e. the vibration sensor is not shaken), the red LED will be switched on and the green LED will be switched off. Again, this may seem counterintuitive but as explained above, it is inverted due to the presence of the interrupt function. The same if statement involving the variable ‘loopcounter’ then follows to ensure an accurate reading from the vibration sensor.

The last part of this if else statement deals with how long the LED stays on when a vibration is detected. As declared in the beginning, the long variable ‘awake’ is now used where it is set equal to the value of millis() minus the value of variable ‘starttimer’. This essentially means that ‘awake’ is the length of time that the vibration was detected for (i.e. the length of time from when the sensor receives a HIGH signal to when it switches back to the default LOW signal). A final if statement then states that if the length of time that the vibration was detected is greater than the long variable ‘betweenTime’, set the boolean variable ‘val’ back to 0, switching the LED back to its default state. Feel free to alter the value of the variable ‘betweenTime’ for the LED to be switched on for a longer or shorter time when a vibration is detected.