How to Stop Grandma’s Wheelchair If She Goes Out of RC Range

Okay, so he doesn’t have Grandma riding in it that we know of, but [zim] recently decided to turn a Jazzy mobility chair into “a radio-controlled platform for mischief”. RC offers more range than wifi or bluetooth, and he was able to find a reasonably priced secondhand radio on Craigslist. However, he found out that in the event of signal loss, the receiver keeps sending the last commands to the speed controller. [zim] didn’t want his 150 lb (68kg) mischief platform getting loose, so he devised a fail-safe that cuts power to the motor when the signal is lost.

[zim] discovered that the receiver returns channel 3 (the throttle) to a preset condition whenever the signal is lost. He used a 24V HVAC relay controlled by an Arduino Nano to sample the PW on channel 3 and shut it off when either the throttle or the signal are cut.

If Grandma is feisty, you could build this caged-in version with a shopping cart.

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A Simple LED Flashlight Composed of a Relay and a Magnet

In our tips line we sometimes receive hacks that are amazing just because of their ingenuity. This relay-powered flashlight is definitely one of them. It has been named RattleGen by its creator [Berto], who apparently often makes simple hacks used in his everyday life (have a look at his YouTube channel).

To understand this hack, you first need to know (in case you didn’t already) that a magnet moving near a conductor (here a coil) induces a voltage at its terminals. This is called electromagnetic induction. In the picture you see above, you may distinguish a disassembled relay with a magnet located on the lever’s end. As a ferromagnetic metal is already placed inside the coil, the lever is by default ‘stuck’ in this position. By continuously pressing the latter on its other end, important voltage spikes are created at the coils terminals. [Berto] therefore used a bridge rectifier to transform the AC into DC, and a 1000uF capacitor to smooth the power sent to his super bright LED. A video of the system in action is embedded after the break.

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Recliner Sofa Given the Power of the Pi

pi-sofa

If you go to buy a sofa these days you’ll not only be greeted with the option of one or more reclining positions, but a fully modern unit comes with motorized reclining. That simply wasn’t convenient enough for [Nicki] and [Kevin] who wanted to control the feature from a smartphone rather than a physical interface (buttons) on the side of the furniture. What resulted is the PiSofa, a Raspberry Pi connected to the furniture’s electronics with the help of a relay board.

This is most certainly a hack, but no doubt one with a lot of finesse. Check out that white PCB. That’s right, it’s a factory spun board to keep things nice and neat. They went with one of our favorite tricks by housing everything inside of a food storage container. After some Ruby coding the Pi now has complete control of the sofa. We’re not overstating this. It literally is the only way to control it because the original buttons no longer work. But that’s okay, turns out not only does it work with their smartphones, but with a [Kevin's] Pebble watch as well.

We can’t think of any past hacks that specifically targeted the couch. But here’s a hammock that you can drive down the street.

Hackaday Links: December 8, 2013

hackaday-links-chain

Let’s start off with some high voltage. Here’s a sweet Jacob’s Ladder build from [Robert]. The site hosting his short writeup has been up and down for us so here’s a cache link.

Speaking of high voltage, if you want to switch mains with your project [Tom] has a breakout board for cheap mechanical relays. [via Dangerous Prototypes]

[Dario] made his own version of an electronic Advent calendar [translated]. There are no numbers, you must solve the mystery of the flashing LEDs to figure out which package goes with each day.

If you ever work with lighted arcade buttons here’s a guide for swapping out the light for an RGB LED. This hack uses through-hole LEDs. We’ve actually seen a surface mount hack that includes a PCB to mimic the old bulbs.

Next time you stay overnight at an event you can give yourself the best view in the campground. This tiny little camper was mounted on a scissor lift! That first step on the way to the Porta Potty is a doozy! [via Adafruit]

[Žiga] was nice enough to demonstrate this smart-watch hack by displaying our name and logo (we love pandering!). It features the MSP-WDS430 which is a surprisingly stylish offering from Texas Instruments. In addition to analog clock hands it has an OLED display driven by the MSP430 inside.

Here’s a quick PIC-based metal detector which [Nicholas] built.

And finally, [Chet] saw the oil tank level sensor we featured this week. He built a nearly identical system earlier this year. The oil level sensor works in conjunction with the custom thermostat he built around an Android tablet.

Arduino Astronomic Clock Automates Lights

ardAst

[Paulo's] garden lights are probably a bit more accurately automated than anyone else’s on the block, because they use latitude and longitude clock to decide when to flip the switch. Most commercial options (and hobbiest creations) rely on mechanical on/off timers that click on an off every day at the same time, or they use a photosensitive element to decide it’s dark enough. Neither is very accurate. One misplaced leaf obscuring your light-dependent resistor can turn things on unnecessarily, and considering the actual time of sunset fluctuates over the year, mechanical switches require constant adjustment.

[Paulo's] solution addresses all of these problems by instead relying on an algorithm to calculate both sunrise and sunset times, explained here, combined with swiftek’s Timelord library for the Arduino. The build features 4 7-segment displays that cycle through indicating the current time, time of sunset and of sunrise. Inside is a RTC (real time clock) with battery backup for timekeeping along with an Omron 5V relay to drive the garden lamps themselves. This particular relay comes with a switch that can force the lights on, just in case.

Check out [Paulo's] project blog for the full write-up, links to code and more details, then take a look at some other home automation projects, like the SMS-based heater controller or occupancy-controlled room lighting.

Microslice: The Tiny Arduino Laser Cutter

microslice

[SilverJimmy] already had a full-sized 50 watt laser cutter, but he decided to try his hand at putting together something smaller and microcontroller-driven. The result is this adorable little engraver: the MicroSlice.

To keep the design simple, [SilverJimmy] opted for a fixed cutting table, which meant moving the cutting head and the X-Axis as a unit along the Y-Axis. The solution was to take inspiration from gantry cranes. He snagged a couple of stepper motors with threaded shafts, designed the parts in Inkscape, then fired up his full-size cutter to carve out the pieces. An Arduino Uno and the relays for the laser and fans sit on the MicroSlice’s bottom platform, and two EasyDriver motor controllers sit above them on the next layer.

Swing by the Instructables for more details including the source code, and to see a video of the engraver below. [SilverJimmy] sourced his laser from eBay, but check out the engraver from earlier this year that used a DVD diode.

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How Do You Build a Relay CPU?

relay

The Hackaday tips line is always full of the coolest completed projects, but only rarely do we see people reaching out for help on their latest build. We’ll help when we can, but [Tim]‘s relay-based CPU has us stumped.

[Tim] already has the design of his relay CPU completed with a 12-bit program counter, sequencer, ALU, and a transistor-based ROM. The problem he’s having deals with the mechanics and layout of his homebuilt CPU. Right now, all the relays (PC pin, we guess) are glued top-down to a piece of cardboard. This allows him to easily solder the wires up and change out the inevitable mistakes. This comes with a drawback, though: he’s dealing with a lot of ‘cable salad’ and it’s not exactly the prettiest project ever.

The ideal solution, [Tim] says, would be a PCB with through-hole plating, but this isn’t easy or cheap for the home fab lab. We’d suggest some sort of wire wrap setup, but proper wire wrap sockets and protoboards are for some reason unreasonably expensive.

If you have an idea on how to do the mechanical layout and connections of a relay-based computer, drop a note in the comments. [Tim] has a very cool project here, and it would be a shame if he were to give up on it due to a lack of tools.

Video below, and if you’re having a problem with a project, feel free to send it in.

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