DIY Earthquake Detector

Some animals seem to be able to detect earthquakes. Some animals also navigate using the earth’s magnetic field. From the idea that there may be some relationship with these two things, this experimental earthquake detector was born.  [Bob Davis] built this device, which uses an Arduino and several Hall effect sensors to detect and record magnetic fields. Possibly after enough data is recorded, a correlation can be found between the two phenomena.

The sensors in this device are arranged to measure magnetism in four directions as well as in the vertical axis. Part of the idea behind this is that before an earthquake the quartz in the ground moves producing a magnetic field.

In the video after the break, Bob gives some background on the theory behind this device and talks about the first version (built way back in the year 2000) which uses a PC for control and recording. Really interesting stuff so be sure to listen to Bob’s explanation after the break. Continue reading “DIY Earthquake Detector”

Arduino levitation

Here’s the proof that Arduino is a tool for serious prototyping and not just a toy. [Norbert Požár] built a magnetic levitation device that combines an Arduino with an electromagnetic driver circuit and a magnetic field sensing circuit. Unlike other other levitation setups that use optical sensing, this implementation uses a hall effect sensor on the electromagnet to maintain the distance between it, and the permanent magnet it is holding in midair. Check out the embedded video after the break and browse through the overview page so see how pleasing it is to do away with a frame around the floating object. This makes us wonder if it could be inverted in a way similar to that magnetic scale.

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Magnetic digital scale

Above you see a solenoid being used as a digital scale. The magnetic field from the coil in the base levitates the platform above, where a load to be measured is place. This floating platform has a permanent magnet in it, hovering above a hall effect sensor in the base. As the distance between that magnet and the sensor changes, the measurable magnetic field changes as well. The hall effect sensor is linear so the measured value can easily be correlated with a weight. In the video after the break [Vsergeev] demonstrates the device using test weights to show off its 0.5 gram resolution. He thinks that with a few hardware improvements he could easily achieve 0.1g accuracy.

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Spinning POV clock done oh-so-right

[Kizo] built an extraordinary persistence of vision clock. The design uses a PC cooling fan to spin the propeller-like PCB. As it goes around, a hall effect sensor synchronizes the illumination of the LEDs to draw the display. Power for the rotating electronics is transferred wirelessly via a transformer on the base and coil on the spinning board. The final version uses an ATmega324 microcontroller running at 20 MHz and has an IR receiver for changing the settings. The 3000 lines of code bring a lot of bells and whistles, including a menu system with a huge amount of settings from tweaking the clock display, to font selection for scrolling messages. Take a look at the demo after the break. The double-sided board looks like it’s pretty difficult to etch at home, but as you can see from the forum post (translated), [Kizo] did a great job on this build from start to finish. Continue reading “Spinning POV clock done oh-so-right”

Simple automatic LED lamps


[woody1189] put together some automatic lighting for his closet. Nine LEDs are grouped into three lamps and controlled by a hall effect sensor. He prototyped this on an Arduino and then migrated over to an ATtiny85. Although the current implementation could be accomplished without a microcontroller, we’d love to see some firmware improvements such as an auto shutoff for when you forget to close the closet door. The hall effect sensor seems to pop up in a lot of projects so make sure you get a few of them with your next parts order. Video of this in action after the break.

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