AVR Atmega based PID Magnetic Levitator

[Davide] saw our recent post on magnetic levitation and quickly sent in his own project, which has a great explanation of how it works — he’s also included the code to try yourself!

His setup uses an Atmega8 micro-controller which controls a small 12V 50N coil using pulse-width-modulation (PWM). A hall effect sensor (Allegro A1302) mounted inside the coil detects the distance to the magnet and that data is used by a PID controller to automatically adjust the PWM of the coil to keep the magnet in place. The Atmega8 runs at 8Mhz and the hall effect sensor is polled every 1ms to provide an updated value for the PWM. He’s also thrown in an RGB LED that lights up when an object is being levitated!

So why is there a kid with a floating balloon? [Davide] actually built the setup for his friend [Paolo] to display at an art fair called InverART 2013!

After the break check out the circuit diagram and a short demonstration video of the device in action!

Oh yeah, those of you not impressed by magnetic levitation will probably appreciate acoustic levitation.

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Hacking grandfather clock accuracy while it’s still ticking

grandfather-clock-tweaking

[Keith] got his hands on a few grandfather clocks. Apparently the price tag is greatly reduced if you are able to get them second-hand. The mechanical timepieces require weekly winding, which is a good thing since you’ll also need to correct the time at least that often. But this drift got [Keith] thinking about improving the accuracy of these clocks. He figured out a high-tech way to adjust the timepiece while it’s ticking.

The first thing he needed was a source of super-accurate time. He could have used a temperature compensated RTC chip, but instead went the more traditional route of using the frequency of mains power as a reference. The next part of the puzzle is to figure out how to both monitor the grandfather clock and make small tweaks to its pendulum.

The answer is magnets. By adding a magnet to the bottom of the pendulum, and adjusting the proximity of a metal plate positioned below it, he can speed up or slow down the ticking. The addition of a hall effect sensor lets the Arduino measure the rate of each swing and calculate the accuracy compared to the high voltage frequency reference.

Theremin takes the touch out of multitouch

Multitouch builds are all the rage now, so it’s not surprising someone would come up with a multi-touchless interface sooner or later. [Hanspeter] did just that; his Multi-touchless ribbon controller, a.k.a. Polymagnetophonic Theremin is multi-touch without the touch.

[Hanspeter]’s touchless ribbon controller uses an array of 24 Hall effect sensors that activate whenever a magnet mounted on a thimble is placed near a build. These sensors go to an ARM-equipped Maple Mini to record multitouch events and send them out over Ethernet.

Even though [Hanspeter] is only using his “multi-touchless ribbon sensor” as a theremin, there’s no reason why it couldn’t be put to other uses. It’s entirely possible to place several of these magnetic sensors in an array and build a real Minority Report interface where the user interacts with a computer without touching anything.

After the break is a video demo showing off how much control [Hanspeter] can get with the thimble/magnet setup. There’s also a few demo songs made with SuperCollider showing off a trio of sitar/Moog/harpsichord synths.

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Improving your flight sim experience with Hall effect sensors

hall-effect-controls

[Gene Buckle] built himself a nice custom cockpit for playing Flight Simulator, but during use he found that the gimbal he constructed for the pitch and roll controls was nearly unusable. He narrowed the problem down to the potentiometers he used to read the angle of the controls, so he set off to find a suitable and more stable replacement.

He figured that Hall effect sensors would be perfect for the job, so he picked up a pair of Allegro 1302 sensors and began fabricating his new control inputs. He mounted a small section of a pen into a bearing to use as an input shaft, attaching a small neodymium magnet to either side. Since he wanted to use these as a drop-in replacement for the pots, he had to fabricate a set of control arms to fit on the pen segments before installing them into his cockpit.

Once everything was set, he fired up his computer and started the Windows joystick calibration tool. His potentiometer-based controls used to show a constant jitter of +/- 200-400 at center, but now the utility displays a steady “0”. We consider that a pretty good result!

[Thanks, Keith]

POV Orb project


It’s been a while since I’ve seen a new twist on POV hardware. This time it’s ‘the Orb’ – comprised of a set of LEDs that rotate to form a sphere. Hopefully more docs are forthcoming. It looks like all the hardware except the motor is contained on the boards inside the sphere – maybe power is provided via the two ends of the spindle? The visuals are driven by a pic C18 with hall effect sensors to provide position readings.
Thanks to [phishinphree] for the tip.

Don’t forget – 6 more days to get in your Design Challenge entry. I’ve gotten some great stuff so far – it’s going to be tough to choose a winner.