Update: Testing The Accuracy Of A Magnetic Rotary Encoder

August 20, 2013 by Mathieu Stephan 27 Comments

A while back we featured a magnetic rotary encoder that [LongHairedHacker] designed. The heart of the system is an AS5043 magnetic rotary sensor which runs from $6.5-$11 and has a 10 bits precision. As we wanted to check if his design was really efficient, he made a test bench for it.

For 360 degrees, a 10 bits precision means a ±0.175º accuracy, which is quite impossible to check with conventional measurement equipment. The first approach he thought of was to attach a mirror to the encoders axis and point a laser beam at it. The laser beam would be reflected across the room to a big scale, but the minimum required distance would have been 5 meters (16 feet). So he preferred attaching a motor to the sensor, rotating at a given speed and measuring the sensor output.

In the first part of his write-up, [LongHairedHacker] lays the math which explains the different kinds of errors that should be expected from his setup and sensor. He then proceeds with his test, where an ATMEGA8 based board is used to send the measured position to his computer. It should be noted that [LongHairedHacker] currently uses the time spent between two received measurements on his computer as a time base, but he is planning on time stamping the data on his board in the next future. Nevertheless, he managed to measure an average ±0.179º accuracy with his simple test bench, which is very close to the manufacturer specification.

Here is the link to our original post about his sensor.

Salvaging Parts From Broken Roomba Robots

July 8, 2013 by Mike Szczys 11 Comments

salvaging-parts-from-broken-roombas

The great thing about hacking on Roombas is that iRobot used quality parts to build them. [Jason] got his hands on a broken 5XX series Roomba and posted an article about how he reused the salvaged parts.

What you see above is one of the results of his work. This little bot takes commands from an IR television remote control. But he also used the setup to make a self-balancing bot. The two motors from the Roomba have magnetic rotary encoders with 8-bit resolution. Pair this with a well-tuned PID algorithm and you’re in business. The video below shows him testing a motor with his PID code.

You don’t get very much info on the guts of the donor robot. If that’s what you’re looking for you need to look at [Dino’s] Roomba 4000 teardown.

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Autonomous RC Car Navigates By Waypoints

June 16, 2013 by Mike Szczys 8 Comments

autonomous-rc-car

Check out this autonomous RC car which [Jason] built for the chipKIT design challenge. It’s been able to successfully navigate a planned route taking just a few waypoints as inputs.

Obviously this uses a chipKIT as the controller, the max32 to be specific. [Jason’s] write-up shows off all of the components of the design, but you’ll have to head over to his recently posted update to hear about the custom board he had spun to host them all. It starts with a GPS module, but that’s only accurate enough to give the rover the big picture. To handle getting from one waypoint to the next successfully he also included a gyroscope which provides very accurate orientation data, as well as optical encoders on the wheels for on-board distance traveled information.

We hope he’ll keep refining the design and make a trip to next year’s Autonomous Vehicle Competition.

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Microscope Ring Light With A Number Of Different Features

April 3, 2013 by Mike Szczys 41 Comments

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Microscopes magnify light. It makes sense that having more light reflecting off of the subject will result in a better magnified image. And so we come to Aziz! Light! It’s [Steve’s] LED light ring for a stereo microscope. It’s also a shout out to one of our favorite Sci-Fi movies.

He’s not messing around with this microscope. We’ve already seen his custom stand and camera add-on. This is no exception. The device uses a fab-house PCB which he designed. It boasts a dual-ring of white LEDs. But the controls don’t simply stop with on and off. He’s included two rotary encoders, three momentary push switches, and three LEDs as a user interface. This is all shown off in his demo video after the break.

An ATtiny1634 is responsible for controlling the device. When turned on it gently ramps the light up to medium brightness. This can be adjusted with one of the rotary encoders. If there are shadows or other issues one of the push buttons can be used to change the mode, allowing a rotary encoder to select different lighting patterns to remedy the situation. There are even different setting for driving the inner and outer rings of LEDs.

We haven’t worked with any high-end optical microscopy. Are these features something that is available on commercial hardware, or is [Steve] forging new ground here?

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A Wearable Pipboy 3000

November 14, 2012 by Mike Szczys 20 Comments

[Zachariah Perry] builds a lot of replica props, and judging from the first few offerings on his blog he’s quite good at it. We enjoyed looking in on the Captain America shield and Zelda treasure chest (complete with music, lights, and floating heart container). But his most recent offering is the wearable and (kind of) working Pipboy 3000 from the Fallout series.

From his description in the video after the break it sounds like the case itself came as a promotional item that was part of a special edition of the game. He’s done a lot to make it functional though. The first thing to notice is the screen. It’s domed like the surface of a CRT, but there’s obviously not enough room for that kind of thing. The dome is made from the lens taken out of a slide viewer. It sits atop the screen of a digital picture frame. [Zachariah] loaded still images from the game into the frame’s memory, routing its buttons to those on the Pipboy. He also added a 12 position rotary switch which toggles between the lights at the bottom of the screen.

A little over a year ago we saw a more or less fully functional Pipboy. But that included so many added parts it was no longer wearable.

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Remote Shutter Module Uses LCD Screen For Setup

May 30, 2012 by Mike Szczys 5 Comments

Here’s a full-featured remote shutter project which [Pixel-K] just finished. It seems that he’s interested in taking time-lapse images of the cosmos. Since astrophotography happens outside at night, this presented some special design considerations. He wanted something that he could configure in the dark without zapping his night-vision too much. He also wanted it to be easily configured with a pair of gloves on.

The project enclosure is a 4x AA battery box. He removed the partitions between each cell, leaving plenty of room for the guts. Inside you’ll find a lithium battery and a micro-USB recharger board. It powers the Arduino mini pro which drives the 1.8″ LCD screen and actuates the optoisolator which is responsible for triggering the camera. On the right you can see the clear knob of the clickable rotary encoder. All of the user settings are chosen and selected using just this one knob.

He’s already tried it out on a 6-hour shoot and had no battery life problems or other issues.

Building A Magnetic Rotary Encoder

March 8, 2012 by Mike Szczys 15 Comments

[Long Haired Hacker] has undertaken a high-resolution 3D printer build. He got his hands on some motors to drive the build platform but it doesn’t have a built-in encoder. He knows that optical encoder wheels can have problems due to dirt and grim as well as ambient light so he set out to find a better way of providing feedback to the controller. He ended up building his own magnetic rotary encoder which is shown above.

At the heart of the system is an AS5043 magnetic rotary sensor. The chip, which runs from $6.50-$11, can detect and report the rotation of a magnetic field with great precision. The rotation data can be read out in degrees using SPI, but it sounds like there’s also grey code output on a few pins if that suits your needs a bit better. The magnet which the chip measures is mounted in a sleeve milled to seat inside of a bearing ring.

The 3D printing method [Long Haired Hacker] has chosen uses a projector and light-cured resin to achieve the kind of results seen in this other hi-res printer.