Solar Powered Lawn Mower Cuts the Grass So You Don’t Have To

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It takes a lot of power and energy to keep grass levels down to an appropriate level; especially when it’s hot out. If cool glasses of lemonade aren’t around, the task at hand may not be completed any time soon causing the unkempt blades of green (or yellow) vegetation outside to continue their path of growth towards the sun.

Instead of braving the oven-like temperatures which will inevitably drench the person in sweat, this solar powered robot has been created ready to take on the job. With the heart of an Arduino, this device shaves down the grass on a regular basis, rather than only chopping down the material when it gets too long. This helps to save electricity since the mower is only dealing with young and soft plants whose heads are easily lopped off without much effort.

Internally, the robot’s circuitry interfaces with an underground wiring system that defines the cutting zones within the lawn, and proves to be a simple, accurate, and reliable approach to directing the robot where to go. If the device travels under a shaded area, a battery kicks in supplying energy to the engine. When sunlight is available, that same battery accumulates the electricity, storing it for later.

[Read more...]

Hidden Reed Switches for DIY Home Security

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[Rhys] wanted to secure his home against burglars, but didn’t want to go the normal route of using those bulky plastic magnet and reed switch deals. So he sourced some glass reed switches and made his own completely hidden security system.

By using small glass reed switches [Rhys] was able to mount them flush to the wood paneling just above the window frames. To do this he drilled and then chiseled two slots for the reed switches to go in, with the wires routed into the house. A bit of bondo or drywall filler and some paint later and they are completely invisible! To finish it off he glued small neodymium magnets to the top of the window frame which close the switches. It’s a very clean build and quite inexpensive to do — the possibilities for wiring up your entire home like this are quite tempting!

He’s got the switches installed already… why not couple it all to a complete home security setup? We shared a project last year that does just that!

Electric Imp makes a cat door Tweet its activities

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This Tweeting cat door uses the Electric Imp to read a sensor and report back to the server. The hardware is pretty neat. The board hosts an ARM Cortex-M3 processor and gets on your home network via WiFi. The mini-USB cable simply provides the power. Programming is done over the network. Our own [Brian Benchoff] had a chance to try the Imp out earlier in the Fall.

Monitoring a cat door is as good a reason as any to undertake a project. The hardware added to the board includes a reed switch mounted on the jamb along with a magnet on the door itself. There is also a blue LED that gives a bit of user feedback. The software isn’t quite as easy but it still wasn’t that bad. As with most web-connected projects getting all the parts to talk to each other was a bit of a chore. The Imp reports back to a server on the local network which then activates a PHP script that uses Sen.se to push out a Tweet.

[Thanks Pat]

Morse code flower is trying to tell you something

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To the casual observer this flower looks nice as its illuminated center fades in and out. But there’s hidden meaning to that light. Some of the blinks are longer than others; this flower is using Morse Code.

[Renaud Schleck] wanted to try a few different things with his MSP430 microcontroller. He decided on an LED that looks like a flower as it will be a nice piece of decor to set around the home. To add the Morse Code message he wanted something a bit more eloquent (and less distracting) than purely digital flashing. So he took the dots and dashes of the hard-coded message and turned them into fading signals by using Pulse-Width Modulation.

He free-formed the circuit so that it, and the coin cell that powers it, would fit in the flower pot. A reed switch is responsible for turning the juice on and off. When placed near a magnet the flower begins its gentle playback.

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Adding task lighting inside a desk

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[Mahesh Venkitachalam] wanted to light up the dark recesses of his desk. What good is all that storage if you can’t see a darn thing in there? His solution was to add LED strips which turn on automatically when the door is opened.

The design is quite simple. A 2N2222 NPN transistor is responsible for connecting the ground rail of the LED strips mounted under each shelf. The base of that transistor is held high with a pull-up resistor. But a reed switch always connects the base to ground when the door is shut. Opening the door removes the magnet that keeps that reed switch closed. This allows current to flow from the pull-up to the base, connecting the ground rail to the LED strips and turning them on. You can see the video demo after the break.

One problem that we see with the design is that these are driven by a 9V battery. Over a long period of time that pull-up resistor will drain the cell. You can pick up a magnetic reed switch at the hardware or electronics store that is rated for 500 mA. If you can stay under that with the LED strips, and get one that is open when the magnet is present you will have zero power drain when the lights aren’t being used.

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Revolight clone

[Fabian.E] wanted to light up the rims on his bike, but didn’t want to shell out a bunch of clams to get it done. He came up with this system which uses magnets and reed switches to light up one arc or each bicycle wheel.

He calls it the lightrider and it’s based on the revolights concept. That design uses a microcontroller which is capable of animating patterns when the wheels aren’t spinning. [Fabian's] version can’t do that, but the effect while moving is basically the same. The ring of LEDs around the rim is connected to a battery via a set of reed switches. When these switches move past a magnet on the fork it completes the circuit and switches on that segment of LEDs. The clip after the break gives a demonstration of the finished product, and includes a fast-motion video of the fabrication process.

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An inside look on how reed switches are manufactured

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[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.

[Read more...]

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