Hack a Day

This pulse oximeter is so simple and cheap to build it’s almost criminal. The most obvious way to monitor the output of the sensor is to use an oscilloscope. The poor-man’s stand-in for that is a sound card, which is what [Scott Harden] demonstrates in his write-up.

It uses a concept we’ve seen a few times before. The light from an LED shines through your finger and is measured on the other side by a phototransistor. It’s that light grey plastic thing you see on a patient’s finger when they’re in the hospital. [Scott] went with a common wooden clothes pin as a way to mount and align the sensor with your finger. It is monitored by the simplest of circuits which uses just one chip: an LM324 op-amp. There are three basic stages which he explains well in the video after the jump. The incoming signal is decoupled before being fed to the first amplifier stage. From there it is fed to an adjustable low-pass filter to help eliminate 60Hz noise from AC power in the room. The last stage amplifies the signal again while using another low-pass filter in parallel.

I may sound like I’m being over enthusiastic in this video. I’m not. Everyone who has seen this things it is simply amazing.

M father, an ex Navy man, has told me stories of glowing water since I was little.  Being a person who was obsessed with all things that light up this always stuck with me. I saw a headline one day that someone was making an algae-light. Sadly when I clicked on it, the algae was just there to create oxygen. It was a cool idea, but not what I was hoping for.

That slight disappointment drove me to create a night light using glowing algae. The process could be extremely simple.

1. Buy Algae.

2. set up light for algae (it needs a 12 hour light cycle and putting it in a window sill would kill it due to heat). It needs bulbs labelled 6500k or higher.

3. shake algae at night (it only lights up when agitated, and when it is on its “night” cycle).

I really wanted to add more to this project though, so I decided to put the algae in a klein bottle and build a custom base for it that would allow me to move a BB around inside the bottle using magnets. This would in turn, hopefully, agitate the algae and make it light up.

I built the base with a DC motor in mind. I dropped it in and added power, but the spin was way too fast and the BB wouldn’t “latch” onto a magnet. I was going to build a small Hbridge to do PWM, but I didn’t have the stuff in my drawer-o-parts and didn’t want to make a trip to the store. So, I stuffed a servo in there instead. It worked, and I thought the BB going back and forth was a cool bonus. You can download the files for the base here.

To get a nice strong light, you have to shake the Algae pretty vigorously. I suspected the BB just wasn’t going to perturb them enough to really shine. As a backup, I took one of my kids toys, a “tornado machine” that was basically a water tight tube with a spinning paddle at the bottom. I was right, the tornado machine was much much brighter, but sprung a leak.

The part that is really frustrating is that I just couldn’t catch the effect on video. It seemed bright to my eyes, and a long exposure photo shows it off fairly well, but none of my cameras would get video. I’ve seen videos of this stuff, so I was especially annoyed.

Ultimately, I have moved it to a larger container next to my side of the bed. I tap on it and the result is like a tiny fireworks show in front of my eyes. It is so bizarre and beautiful.

Here’s a .gif I found of the effect. This isn’t my set up, but you can see what I’m talking about here.

This is a fascinating take on building your own pick and place machine. It does an amazing job of automating the hardest parts of hand assembly, while relying on human dexterity to achieve the hardest parts of automation. It’s a semiautomatic pick and place machine driven by an Arduino and controlled by an Android tablet.

The machine is built in two parts. The portion in the upper left feeds components from reels and is fully automated. The portion on the lower right consists of a padded arm-rest which slides smoothly along two axes. A mechanical arm with multiple articulations is attached to the end, culminating in a tip connector for some vacuum tweezers. Right handers are the only ones who will find this convenient, but oh well. The clip after the break shows it in action. The assembly technician first selects the component from an icon on the Android tablet. The reel machine then dispenses that part, which is picked up by the vacuum tweezers using the let hand to switch the vacuum on and off again. If the part orientation needs to be rotated it can done using the jog wheel on the Android app. It smooth, quick, and best of all, clever!

http://www.youtube.com/watch?v=vkPkjBfZXDg

[Home Awesomation] has been working on automating his slat-style window blinds. His focus has been on adjusting the angle of the slats, not on completely retracting the shades. Since the slat angle adjustment requires little torque a servo motor turns out to be just perfect for the job. The good news is that the existing blinds in his house have room in the top enclosure to completely hide his add-on hardware.

The image above is a screenshot from the demo which you can watch after the break. The top enclosure for the blinds is just shown at the top of the frame. Here [HA] is demonstrating a few different control designs which he has been trying out. You can see what looks like a Molex connector with some type of component attached to it. That’s an IR motion sensor and he’s really happy with its performance. He feels the same way about the black momentary push switch sticking down next to the power cable. But his DIY solution that works quite well is the pull string attached to a flexible piece of metal. When that metal bends enough to touch a stationary conductor it completes the circuit, telling the Arduino to start driving the servo.

The main idea behind the project is to poll a temperature sensor, closing the blind automatically to help keep the place cool during the day. We figure if he’s already using a microcontroller to drive the project he might as well throw a cheap Bluetooth in module there and make it controllable with a smart phone.

[via Ariccio]

[Jan] was given this toy keyboard and decided to make it the subject of his next project. In addition to having three octaves of keys it’s got a ton of buttons used to select different modes. He gave it an upgrade by installing his own tone production circuitry seen in the upper right.

His preliminary investigation of the stock components yielded a mystery uC encased in a blob of black epoxy. He wasn’t going to be getting anywhere with that, so he started by figuring out how to use 4051 multiplexers to read all of the keys. Outputs for that were routed to a 20 pin header for easy connection to the synthesizer board he would build in the next part of the project. He based it around an ATmega8, which we know can produce some killer chiptunes audio. Once he had everything working he laid out a circuit board in Kicad to ensure the transplanted circuitry would hold up inside of the toy keyboard. You can hear all of different effects it’s capable of in the clip after the break.

While browsing an oculus rift thread on reddit, I saw someone mention how nice it would be to have some actual mounts for external sensors on their Rift. The idea is that adding additional sensors or cameras will allow us to expand the capabilities of the rift. With something like the Razor Hydra, you can add quick positional tracking (the rift only tracks rotation, not position). With some webcams, you could theoretically do some stereoscopic augmented reality.  Unfortunately, attaching all these things to the rift is a bit of a pain at the moment.

I had all the things right here in front of me to make this happen, so I did! I’ve quickly tossed together two accessories for the Rift.

1. a small bracket that feeds onto the velcro on the back. People will likely use this for “heavy” position sensors. They may be fairly light, but any additional weight on the front of the rift is unwanted.

2. A snap-on face plate that has a modular design. This wold be for mounting cameras on the front of the rift.

All of these files can be downloaded here.

[Tommy Ward] had a big problem with the cord for his laptop power supply. This thing’s not cheap so he figured out a way to fix the frayed cord on his Apple MagSafe. He asserts that the shortened rubber collar on the plug end of the cord is to blame for this type of damage. We think rough use may have something to do with it too, but having had to repair our own feline-damaged power cords we’re not about to start pointing fingers.

To pull off an appropriate fix [Tommy] pries apart the case housing the power converter. This lets him get at the solder connections of the cord. After removing it from the circuit board he clips off the damaged portion of the cable. To reuse the strain relief grommet he drilled out the old portion of wire and insulation, making room for the undamaged cable to pass through, adding a cable tie on the inside to aide in strain relief. The last part of the fix involves gluing everything back together.

If your power supply problems have to do with the computer connector itself there’s a fix for that too.

[Will] has been hard at work on a replacement system for his Hackerspace’s RFID door lock. The original is now several years old and he’s decided to upgrade to a much more powerful processor, adding some bells and whistles along the way.

The control box seen above is the exterior component of the system. It’s a telephone service box like you’d find on the back of most houses in the US. They had a few of these lying around and they are a perfect choice because… well… they’re meant to be locking enclosures that brave the elements. [Will] made the jump from an Arduino which has run the locks for the last three years to a Raspberry Pi board. This gives him a lot of extra power to work with and he took advantage of that by adding a vehicle backup LCD screen for visual feedback. You can see it giving the ‘Access Granted’ message he used during testing but the demo video after the break shows that they plan to do some image scripting to display a head shot of the RFID tag owner whenever a tag is read.

There are several other features included as well. The system Tweets whenever a tag is read, helping the members keep tabs on who is hanging out at the space right now. It also patches into a sliding door which one of the members automated using a garage door opener motor.

Check out this 20″ iMac. Notice anything peculiar? Look closely at the branding above the Apple logo. The only thing that tips you off that this iMac is a hacked together unit is that Acer logo on the replacement screen.

As we’ve so often been caught doing, [Flippy] was browsing eBay for deals. It’s a dangerous activity because you end up falling into purchases like an Aluminum iMac for $35. That led to the purchase of a very slim LED LCD monitor to use as the display. It fits perfectly behind the iMac’s glass bezel, which has a tiny chip in the upper right corner that doesn’t bother [Flippy]. It’s thin enough that this actually left room for him to add in the guts of a MacBook Pro which he had sitting in his unused parts pile. With all of the main components accounted for the rest is really just logistics like routing all of the cable connectors and adding openings for USB ports. What he ended up with is a high-end computer for a low-end price.

Let’s face it, most kegerator builds go something like this: acquire old refrigerator, drill hole for tap, profit. But [GiveMeMyNickelback] recently had the opportunity to do better and he delivered. Above you can see the stylish chest freezer mod that serves up six beers on tap.

Chest freezers are perfect for these builds as their top door design helps keep the cold air inside to boost the efficiency. The trick is to modify them without messing up the insulating properties of the appliance housing. [GMMN's] approach is a common one, build a cuff to go in between the lid and the body of the freezer. He started by building a wooden box open at both the top and the bottom. Many would have stopped there but to bring the bling he tiled the sides and front of that cuff, leaving an empty spot for the shank of each tap. With that taken care of he glued insulation to the inside of the cuff, and added weather-stripping to the bottom to seal with the top of the case. He used the holes from the lid hinge brackets to attach his add-on so that the freeze can be converted back to stock without any sign of his alterations.

We’d love to see a Bluetooth or Wifi add-on that monitors the beer volume in each keg.

[via Reddit]

[Dominic Buchstaller] found this German Greatz tube radio at a flea market. It only cost him about €35 and was in a bit more rough condition than the finished product you see above. He also found that a portion of the original circuitry was missing, making it completely non-function. He cleaned up the case to improve the wife-acceptance-factor, and outfitted it with hardware to make it a web radio.

Adding modern speakers was pretty easy as he was already replacing the original cloth bezel which has several holes and tears in it. A set of elements from some Logitech computer speakers served as the organ donors for this step in the process. As he was trying to keep a stock look he came up with a really neat hack to use the original knobs. The station select happens to have a large metal wheel on the inside which is about a centimeter wide. [Dominic] used the optical sensor from a mouse to monitor the turning of the dial by aiming the sensor at this wheel. Internet connectivity was provided by a wireless router he had on hand. This way he can stream music or play from an SD card he also used in the retrofit.

This boxy monstrosity is big for a reason. It lets you play games on the original hardware of fifteen different gaming consoles. That’s right, we said original hardware. One of the main goals of Project Unity was to keep the stock equipment by making any type of emulation — hardware or otherwise — taboo. The size of the case is a function of how much stuff is actually crammed in there. But the final shape was dictated by the available opening in [Bacteria's] living room entertainment center.

The video after the break walks us through each aspect of the build. We’re floored by the quote of 3,500 hours of build time. But as you get a look at the wiring-hell of each different module it’s easy to understand why it didn’t just build itself. One power supply and one controller make for the least complicated user experience possible. We already looked at a giant switching mechanism that selects one console at a time and the singular controller unit. But [Bacteria] has a lot of other tricks up his sleeve which make this gold mine of a hacking reference piece.

[FlorianH] has all kinds of new features to show off with this generation of his quadcopter project. Just about everything has seen an upgrade or some other kind of tweak since we looked in on the last version of the aircraft.

You’ll find some outdoor flight demo clips after the break. Right off the bat we’re impressed at the rock solid stability of the quadrotor while in flight. Even indoors the last version had a hint of a wobble as the control loop calculated stabilization. Here he borrowed some code from the open source Aeroquad project which helps account for this improvement. But the hardware choices lend a hand too. He moved from an ATmega32 up to an STM32F405RG processor. That’s an ARM chip which he programs using one of STM’s Discovery boards. The motors have all been upgraded as well (if you listen in the demo videos for both models you can hear a difference) and he redesigned the frame, which combines carbon tube with 3D printed parts to keep it light yet strong. The upgrade is every bit as impressive as the original build!

This is a project to keep in mind for the kids next Easter. It uses electronics to light up your eggs instead of dying them (translated).

The project still has one foot in the old tradition as it starts by blowing out the eggs. The larger hole on the bottom, which was used to evacuate the yoke an albumen, ends up being just the right size to insert an LED. You could simply hook these up to a battery and resistor, but [Rene] decided to add some functionality by hiding an Arduino board in the fake grass of the Easter basket. This way the way the RGB LEDs can glow, blink, and rotate through different colors. And the foil covered chocolate bunnies aren’t just for show. He wired them up to the I/O pins of the Arduino to use as a switch. When they’re both placed on the same piece of foil it completes the circuit and starts the light show. See for yourself in the clip after the jump.

Of course for the older kids you’re going to need something more complicated to keep their attention.

We figure we have to start off this week’s links post talking about PETMAN. Boston Dynamics shows off the humanoid robot donning a full chemical suit. It’s a lot scarier than when we first saw it as a couple of legs a few years ago [Thanks Joshua].

Seeing something like that might drive you back to smoking cigarettes. But since that’s pretty bad for your health perhaps you just need a mechanical chain-smoking machine to take the edge off. That thing can really suck ‘em down! [Thanks Mike]

Last week’s links included a bit about the Raspberry Pi 2.0 board version’s reset header. [Brian] wrote in to share a link for adding reset to a 1.0 revision board.

Speaking of RPi, [Elvis Impersonator] is using it to automate his garage door with the help of Siri.

In shop news, [Brad] needed to sharpen a few hundred pencils quickly and ended up melting the gears on his electric sharpener. Transplanting the parts to his drill press gave him more power to get the job done in about six minutes.

And finally, you can forget how to decipher those SMD resistor codes. Looks like surface mount resistors might be unmarked like their capacitor brethren. We were tipped off by [Lindsey] who got the news by way of [Dangerous Prototypes and Electronics Lab]

We’ve thought of doing a project like this ourselves as the dehumidifier we ordered online runs the fan 24/7 no matter what the humidity conditions. But it wasn’t that [Davide Gironi] was unhappy with the features on his unit. It’s that the dehumidifier controller stopped working so he replaced it with one of his own design. The original humidity sensor was mechanical and simply broke. He used an AVR along with a humidity and frost sensor to get the appliance up and running again.

A DHT22 humidity sensor is polled by the ATmega8 chip and compared to the user-adjustable trimpot value. If it is above that threshold the unit is switched on using one of the relays seen in the image above. The one problem you have to watch out for when using compressor cooled appliances is ice accumulation on the radiator. [Davide] uses a thermistor for temperature feedback, switching the compressor off when it gets below 7C and turning it back on again when it is above 12C.

The replacement still uses the reservoir sensor and indicator LEDs. We, however, would recommend using the watchdog timer on the chip to ensure that it is reset if something goes wrong in the code.

Some people know [Tom Murphy] as [Dr. Tom Murphy VII Ph.D.] and this hack makes it obvious that he earned those accolades. He decided to see if he could teach a computer to win at Super Mario Bros. But he went about it in a way that we’d bet is different that 99.9% of readers would first think of. The game doesn’t care about Mario, power-ups, or really even about enemies. It’s simply looking at the metrics which indicate you’re doing well at the game, namely score and world/level.

The link above includes his whitepaper, but we think you’ll want to watch the 16-minute video (after the break) before trying to tackle that. In the clip he explains the process in laymen’s terms which so far is the only part we really understand (hence the reference to voodoo in the title). His program uses heuristics to assemble a set of evolving controller inputs to drive the scores ever higher. In other words, instead of following in the footstep of Minesweeper solvers or Bejeweled Blitz bots which play as a human would by observing the game space, his software plays the game over and over, learning what combinations of controller inputs result in success and which do not. The image to the right is a graph of it’s learning progress. Makes total sense, huh?

[via Reddit]

We like the look which [Emmanuel] achieved with his Raspberry Pi based Squeezebox client. It’s got that minimalist slant that makes it seem like a commercial product at first glance. But one more look at the speakers without grates, the character LCD, and the utilitarian buttons, knobs, and switches tips us off that it’s filled with the hardware we know and love.

Since Logitech announced that it was terminating the Squeezebox line we’ve seen several projects which take up the torch. We’ve seen the RPi used as a Squeezebox server and several embedded Linux systems used as clients. This follows in the footsteps of the latter. The RPi is running Raspbian with the squeezelite package handling the bits necessary to talk to his server. The controls on the front include a power switch, rotary encoder and button for navigating the menus, and a potentiometer to adjust the HD44780 LCD screen’s contrast. The speakers are a set of amplified PC speakers that were liberated from their cases and mounted inside of the wooden box that makes up the enclosure. The in-progress shots of that case look pretty rough, but some sanding and painting really pulled everything together. As you would expect, we’ve embedded the demo video after the jump.

Most 3D printers use stepper motors to control the movement of the extruder head. If you could actually print those motors it would be one more big step toward self-replicating hardware. Now obviously [Chris Hawkins'] working 3d printed stepper motor wasn’t built 100% through 3D printing, but the majority of the parts were. All that he had to add was the electronic driver pieces, magnets, wire, and a few nails.

The coils are made up of nails wrapped in magnet wire. The rotor is a 3D printed framework which accepts neodymium rare earth magnets. The axle is pointed which reduces the friction where it meets the cone-shaped support on either side of the frame. The IC on the upper right is a transistor array that facilitates switching the 20V driving the coils. The board on the lower right is a Digispark, which is an ATtiny85 breakout board that includes a USB edge connector for programming and a linear regulator which is how he gets away with feeding 20V as the source.

Don’t miss the demo video after the break where you can see the motor stepping 7.5 degrees at a time.

[Thomas] and his friends wanted to ring in the new year by setting off some fireworks. To keep a safe distance and have a little fun they built this network controller launcher (translated).

the image on the left shows the build in its unused and pristine state. But by the end of the celebration it look a bit melted and burnt. Still, for the first revision of the system it ended up working pretty well.

We’ve seen several remote fireworks launchers that burn up resistors to light the fuses. But this system is much more reusable. The image on the right shows the heating elements which light the fuses. Younger readers might have no idea what they’re looking at, but every automobile used to come with at least one of these electric cigarette lighters. Just drive 12V through them and they get burning hot relatively quickly. That’s where the car battery on the base comes into play. It is connected to the lighters using some mechanical relays.

In the food container attached to the side of the launcher you’ll find a Raspberry Pi which provides the web connection for the system. [Thomas] wrote code which uses a webpage with some bomb icons as buttons. Check out the video after the break to see him demonstrate how fast one of these lighters will glow red after pressing a button on his smart phone.