An earthquake is an unavoidable and unpredictable natural phenomenon that often causes damage to lives and property. We cannot fight it but we can stay alert and aware using technology that can protect us and the industry. Here a simple earthquake indicator for home and industry using an Arduino and a highly-sensitive ADXL335 (Fig. 1) accelerometer is presented that can indicate vibrations.
This project can be modified and used as a knock-and-shake detector for ATMs, vehicles or door-break alarms. But its main aim is to detect earthquakes and other seismic activities.
We know that accelerometers like ADXL335 are highly sensitive to knocks and vibrations in any of the three physical axes. ADXL335 gives analogue voltage equivalent to imposed acceleration. It has three outputs, one each for of X-, Y- and Z-axes. The three analogue outputs are wired to Arduino Uno ADC pins. Any acceleration caused due to movement in any of the axes is detected by the accelerometer and hence by Arduino ADC.
If motion is violent enough during an earthquake and crosses a certain threshold, a local alarm light (LED) glows, a buzzer sounds as well as a relay energises. While the buzzer and light is for home purpose, relay output is for industrial purpose; it can be wired to a PLC for safety interlocking of any moving machine part and furnace control for shutting these down in case of an earthquake. The threshold adjustment buttons are there for carrying out this task. An LCD has been provided for viewing threshold adjustments and for making the system user-friendly.
Circuit and working
The circuit (Fig. 2) uses Arduino Uno board wired to ADXL335 accelerometer module (connected across CON2) with its ADC inputs, namely, X-axis to A0, Y-axis to A1 and Z-axis to A2. Two pushbuttons through supply of 5V are wired to Arduino Uno interrupt pins 2 and 3 that are pulled down to ground via resistors R2 and R1. These buttons are used for incrementing and decrementing the threshold of vibration detection. A 16×2 LCD (LCD1) is wired in 4-wire mode with Arduino pins contrast control and backlight enabled.
BC548 transistor (T2) is connected to pin 5 of Arduino for switching on the local alarm LED (LED1) and a buzzer connected across CON4. Another BC548 (T1) is connected to pin 10 for de-energising a relay (RL1) in case the alarm is triggered for industrial PLC interfacing for safety interlocks. Pins 11, 12, 9, 8, 7 and 6 are used for LCD control and data lines. When the setup is powered, and while it is still, it reads and stores current accelerometer values in Arduino internal EEPROM regardless of its orientation.
Since the ADC is 10-bit, special header file has been provided with the code. A five-second delay has been provided for all voltages and for the system to be stable before any initial value is read. Arduino’s microcontroller reads all three axes data from the accelerometer and stores in the EEPROM. It also stores the default threshold value of 25 in the EEPROM.
Some conventional indications on the LCD (Fig. 3, Fig. 4 and Fig. 5) are shown here for different working modes. In initialising mode (Fig. 3), system parameters are initialised. In monitoring mode (Fig. 4), the system enters into monitoring mode with current threshold value displayed on the second line of the LCD.
In indicating mode (Fig. 5), the system reads accelerometer values continuously and compares these with previous steady values of the accelerometer, stored in the EEPROM while initialising. If current value differs, that is, if stored value is either more than threshold value in positive side or less than threshold value in negative side, the alarm sounds and the relay is de-energised. This design and coding supports positive as well as negative values in all three axes.
Pushbuttons connected to pins 2 and 3 of Arduino serve as interrupts for incrementing and decrementing threshold values for sensitivity adjustments. For earthquakes, a threshold of 10 to 15 is good. The sensor can also be used to detect knocks and vibrations if the threshold is set to 5 to 8.
The entire setup can be wired and enclosed in a hard enclosure and mounted anywhere in industry or home. Users can also calculate resultant acceleration by using formulae of square root of X2+Y2+Z2, where X, Y and Z are outputs from ADXL335, and then compare the result with the threshold to raise an alarm. Modifications can be done by the user on the same platform, if required.
Software comprises earthQuake.ino with some header files of Arduino.
Download source code: click here
Library File: click here
Ronie Adhiraaj Ghosh is M.Tech from Homi Bhaba National Institute, Mumbai. His hobbies include electronics projects, watch collection, camping and hiking