Want to detect earthquakes and other seismic events—from natural disasters to human activities—right from your workbench? This DIY seismograph project from 2007 uses a sensitive vibration sensor to monitor tremors, including those too subtle for humans to feel.

Natural events like earthquakes, landslides, and meteorite strikes produce seismic waves that travel across the Earth’s surface. In the case of powerful earthquakes, these vibrations can circle the globe multiple times before fading away completely. Seismic activity can also result from human actions, such as natural gas extraction or nuclear testing. Although these man-made tremors are typically too weak to be felt or heard from afar, they can still be detected with a highly sensitive vibration sensor — just like the one used by Gert Baars in the DIY seismograph presented in his project.
 
Seismograph circuit
The signal from the sensor is amplified, filtered, and digitized by an ATtiny, which passes the signal on to a PC.

Circuit Essentials

Traditional seismograph sensors use a mass-spring system to detect vibrations, but they are complex, costly, and require damping to prevent prolonged oscillations. As a simpler alternative, this project repurposed a small 0.5 W/ 8 Ω loudspeaker (8–12 cm in diameter) as a vibration sensor. By placing a weight on the cone, ground tremors cause the speaker to move while the mass resists motion, generating a voltage in the coil due to its inertia — effectively turning the speaker into an affordable and sensitive seismic detector.

“The signal from the loudspeaker is first amplified and then followed by a filter to eliminate hum and to reduce noise,” Baars explained. “The signal is then presented to the ADC input of an ATtiny microcontroller. Once the conversion is completed, the microcontroller sends the signal to the computer via the serial link. A program running on the computer or laptop converts this data into a graphical representation, which allows the user to read the time and strength of the seismic activity. In two smaller windows you can see in real time the amplitude and the frequency spectrum of the signal.”
 
Seismograph project
The board and components

Software and Specs

The assembler-written software in the microcontroller had the simple task of transmitting the ADC-result when requested. Because the particular controller didn’t have a UART, this was done with additional software. The PC application was programmed in the Delphi programming language.

Specifications:
 
  • 0.5 to 25 Hz bandwidth (50 S/s)
  • Sensitivity from a few micrometers (μm)
  • Sensor circuitry is powered from the PC
  • Serial port: 2400 baud, 8 bits data transmission

The Seismograph Project

The article, “Seismograph: Lautsprecher als Schwingungssensor,” appeared in Elektor May 2007. You can read the article free during the two weeks following the publication of this news item. If you start a project of your own, consider sharing your progress on the Elektor Labs platform!
Editor's Note: This article originally appeared in a 2007 edition of ElektorMag. Given the project’s age, some components, PCBs, products, or links may no longer be available. However, we believe the content remains might inspire you to start new electronics projects at your workbench.
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