An inside look on how reed switches are manufactured

reed-switch

[York] wrote in to share a video he stumbled across while researching reed switches and relays, which documents the tightly controlled process through which they are produced. Like many other electronic components out there, we usually don’t give a lot of thought to how they are made, especially when the final cost is relatively small.

For something often taken for granted, the process is an incredibly precise one, requiring a clean room environment the entire way through. The video follows the production line from beginning to end, including the soft annealing of the contacts to remove magnetic remanence, the sputtering process that applies sub-micron thick conductive coatings to the contacts, through the laser cutting and sealing of the glass tubes that make up the body of the switch.

At the end of the day, the video is little more than a manufacturer’s promotional video, but it’s worth the 8 minutes it takes to watch it, if only to satisfy your curiosity as to how they are made.

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Easy workout logging with Ethernet-enabled exercise bike

It will be easy to keep your exercise routine on track if you don’t have to do anything at all to log your workouts. [Reefab] developed this add-on hardware for his exercise bike that automatically logs his workout on the Internet.

He’s using RunKeeper to store and display the workout data. They offer a token-based API which [Reefab] implemented in his Arduino sketch. The hardware to grab data from the exercise bike is quite simple to set up. A rare-earth magnet was added to the fly-wheel with a reed switch positioned next it in order to measure the number and speed of rotations. This is exactly how a consumer bicycle computer works, needing just one accurate measurement corresponding to how far the bike travels with each revolution of that wheel.

In addition to the networked-logging feature [Reefab] included a character display so you can follow your speed and distance data during the workout.

Semaphore signal replica perfect for the train buff in your life

semaphore-signal

[John Philip’s] brother has a sizable room set aside for his model railroad setup, and he was looking for something interesting to add to his brother’s collection. Rather than construct something for the railroad itself, he decided that an early 1900’s-style semaphore railroad signal would make a great novelty item for the room.

The project started with [John] scouring the Internet for colored signal lenses. Once he found a set that worked for him, he crunched some numbers to ensure that the rest of the semaphore box stayed true to original scale. Inside the signal’s case you will find a small regulator board for his light source, an Arduino, and a motor controller board to actuate the arm.

To ensure that the signal arm is always perfectly positioned, he installed a pair of reed switches on either side of the case, enabling the Arduino to auto-calibrate the signal’s position each time it is powered on. At first, this control scheme might strike you as a bit over the top, but we really like the fact that the signal can always configure itself to function perfectly, even if someone tinkers with/bumps into/moves the arm at any point.

Be sure to stick around to see a short video of the semaphore signal in action.

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Motorized coop door lets the chickens out for you

[Larry] and [Carol] just upgraded the coop to make their lives easier, and to help keep the chickens happy. The image above is a chicken’s-eye-view of the newly installed automatic door. It’s a guillotine design that uses the weight of the aluminum plate door to make sure predators can’t get in at night. This is much easier to fabricate than a locking coop door would have been. Some leftover aluminum channel guides the door on either side, with a spool above it to wind up some rope, thereby lifting the door.

You can see the belt-drive motor is also mounted inside, out of the element. To the right of the image you can just make out a plastic food container. This protects the electronics from the elements. Inside you’ll find an H-bridge to drive the motor, a real-time-clock to make sure the schedule is well-timed, and an Arduino. There are a couple of reed switches which let the microcontroller sense the position of the door.

After the break you can see a demonstration video, as well as a slide show with build details. The motor is pretty quiet and, although it spooks the chicken in the demo just a bit, we’d be they’ll be used to it in no time.

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Keeping tabs on your pets’ busy lives

mouse_wheel_tracking

[Stephen’s] daughter has a pair of mice she keeps as pets, who happen to be quite active at night. After they kept her awake for an entire evening by running like mad in their treadmill, they were moved from her bedroom. Since they were so active in the treadmill, [Stephen] thought it would be cool to try measuring how much the mice actually ran each night.

To keep track of their activity, he built a simple circuit that records how many rotations the treadmill makes. He fitted it with a rare earth magnet, installing a reed switch on the outside of case that ticks off each spin of the wheel. Any time the wheel starts moving, his PIC begins counting the rotations, displaying them on a 7-segment LED display. To mitigate data loss in the event of a power outage, the PIC stores the current number of rotations in its EEPROM every 10 seconds or so.

The counter keeps track of the total number of rounds the mice have completed, which his daughter uses to manually calculate their running sessions. Since they started tracking the mice, they have run over 700,000 rounds, sometimes completing as many as 20,000 in an evening.

We think it’s a pretty cool project, especially since it makes it fun for his daughter to stay involved in her pets’ lives.

Slot car lap timer/counter

For his first project using the TI Launchpad [VOJT4] built a lap timer and counter for slot cars. For us it’s always hardest to come up with the idea of what to build and we think he found a great one here.

Each time a car passes the finish line of the track it trips a reed switch that was hot glued to the underside of the track segment. Both reed switches have a capacitor to smooth out the inputs (is this acting as a hardware debounce?). The time and lap number are then pushed to a graphic LCD by the MSP430G2553.

You must be logged into the forum where [VOJT4] posted the project in order to see the images. Because of this, we’ve embedded them (including the schematic) after the break along with a demo video. But do take a look at his project thread to hear his thoughts and peruse the code he wrote.

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Automated chess set does it from below

You can get class credit for the coolest things these days. Take for instance, this Automatic Chessboard that [Brian] and [James] built for the final project in one of their classes this spring. We just looked at a robotic chess setup on Monday that used a gripper mounted on a gantry to move the pieces. This one’s a lot more user-friendly and borders on magical. That’s because the moving parts are all located below the board and could be hidden from view if a proper case were built around the edges.

There are two main components to this build. The first is a grid of reed switches that detect the moves made by a human. This works because each piece the human player uses has a weak magnet glued to the bottom which is just strong enough to actuate the reed switch and let the computer sense what move was just made. On the robotic side of things this works like a plotter. Each of the computer’s pieces has a metallic disc glued to the base. What basically amounts to a plotter under the board uses rare-earth magnets to grab the computer’s piece and drag it to the next playing position.

The use of two separate magnetic systems provides some interesting design challenges. You can see the device in action in the video after the break, and a full writeup and source code package is available at the blog linked at the top of this feature. But for your convenience we’ve also mirrored the PDF whitepaper after the break which lays bare all of the juicy details.

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