What uses a fire extinguisher, a bike pump, and provides hours of probation, community service, and possibly jail time? If you said an automatic graffiti writer you’re correct! [Olivier van Herpt] calls this little job the Time Writer. We call it defacing property… but tomato, tomahto.

Details are a bit scarce, but you get a fine overview of the system from the video after the break. [Olivier] tagged the post as Arduino; it’s obviously running the dot matrix printer made up of seven solenoid valves on a metal rod. These are fed ink via a tube connected to a fire extinguisher which serves as the reservoir. The bike pump is used to pressurize the enclosure so that a pump isn’t necessary when out and about.

Obviously you shouldn’t try this at home, but let’s talk about possible improvements as an academic exercise. First off the mix of the ink/paint needs to be reigned in to get rid of the dripping. We’d also like to see the inclusion of some proper spray can nozzles to tidy up the results. That, paired with an IMU board should be able to smooth out the printed designs.

This might make an interesting add-on to that rainbow graffiti writer.

[joe] and [ryan] built Thumper for their high school FIRST robotics team. The cannon itself is a solenoid-fired compressed air launcher that gets its juice from three large PVC tanks stored in the box below the turret, and the cannon is able to be fired nine times between visits to the air compressor. It was intentionally designed to resemble an M2 Browning 50 Caliber heavy machine gun, with the two vertical handles and boxy body.  They finished construction in about a week with a budget of only $300. When they saw that a lot of their friends had also built cannons, they scrounged for parts from their garages to re-use to build the mobile platform simply for one-upmanship sake. The motor and drive-train propelling this behemoth came out of a 1980s-era mobile X-Ray machine that had been discarded by a local hospital. The rear wheels were specially modified to fit the drivetrain, and the front end is a chopped, hacked, and welded axle and steering mechanism from an old lawn tractor. Sections of unistrut form the rest of the frame.

[joe] and [ryan] were even asked to bring Thumper to their high school prom as a unique way to hand out T-Shirts for the evening. Unfortunately, there’s no website for this build.

See video of Thumper in action with a Nerf Football after the break. Hack A Day even got to take it for a spin around the Power Wheels Racing Series track at Maker Faire KC!

After the electromechanical timer on [Paul Canello's] washing machine broke for the third time he decided he needed to stop repairing it and find a more permanent fix. He decided to build his own microcontroller-based system for washing his clothes (translated). Caution: The image links on [Paul's] page seem to be broken and will unleash a never-ending storm of empty pop-up windows if you click on them. We’ve embedded all of the images after the break to save you some hassle.

The controller on a washing machine is nothing more than a mechanical alarm clock. It starts the cycle, then moves through various modes based on the passage of time. [Paul] started his hack by observing how long the delay between cycles was meant to be, and recording which parts of the machine were switched on and off at each stage.

It turns out that when the mechanical knob is turned, it reroutes how water flows through the detergent chamber. Since that knob won’t be in the new system [Paul] came up with a way for the microcontroller to handle this by using a servo motor. The rest of the control involves relays to control the motor, and solenoid valves for the water. There are also pressure switches that give feedback for the level of the water in the machine. A PIC 16F872 serves as the new controller, with the help of a 7 segment display, a buzzer, and a pair of buttons as the user interface.

This is an older project, but after reading about the Arduino controlled dishwasher [Ramiro] sent us a link. Thanks!

Just in time for Valentine’s day, [Adam Meyer] and the folks over at tellart.com have put together a little project they call the “Love Song Machine“. Using a web-based form, anyone can submit a song, which will then be played on a system of bells that they have set up in their office. You can choose from several pre-defined love songs, or you can create your own unique arrangement with which to serenade them. Once you are ready to go, your song will be queued up, and you can watch a video of your creation as it is being played.

The system is comprised of 8 solenoid-actuated bells which are all controlled by the Arduino they have hooked up to their web server. It’s a pretty fun idea, and there are sure to be plenty of people submitting songs, so get yours in before things get too busy!

Keep reading to see a video preview of their system in action.

Above you see a solenoid being used as a digital scale. The magnetic field from the coil in the base levitates the platform above, where a load to be measured is place. This floating platform has a permanent magnet in it, hovering above a hall effect sensor in the base. As the distance between that magnet and the sensor changes, the measurable magnetic field changes as well. The hall effect sensor is linear so the measured value can easily be correlated with a weight. In the video after the break [Vsergeev] demonstrates the device using test weights to show off its 0.5 gram resolution. He thinks that with a few hardware improvements he could easily achieve 0.1g accuracy.

[Chris Marion] knew he wanted to play with fire, or more accurately with fireball spewing valves, but he need a good project in which he could use them. Inspiration finally struck and he built this controller that matches fireballs to the fret buttons on a Guitar Hero controller. There’s quite a lot that goes into this but we think that he hit a home run. The basic components are a manifold with electronically actuated valves, another manifold for the pilot lights, and a modified Guitar Hero controller.

To interface the controller he used an Arduino along with [Bill Porter's] PS2 library to read signals from the buttons. But the real labor intensive part of the build came with the manifold. There’s a hardware store’s worth of fittings and flexible copper pipe that go into that assembly. In the end this all came together in just one week.

[Thanks Bill]

This hack’s old as dirt to be sure, but new to us and a great accomplishment. The plane above, which is meant to fly without an operator, has been given RC control thanks to parts from that little car. The transmitter and receiver pair are the obvious transplant, but how do you add steering to a $7 plane that wasn’t manufactured to have that feature? The tail was cut and reconnected with mylar hinges to turn it into a rudder. A rare earth magnet and a coil are also thrown into the mix to provide movement. Basically this is a simple solenoid where the coil pushes against the magnet when energized, actuating the rudder. This in combination with an upgraded motor allows for both speed control and yaw. It doesn’t look like you can control roll and pitch but what more can you really expect?

This would be a nice first step on that path to building an epic flying camera rig.

[Thanks Rob]

Learn to manufacture your own solenoids and then use them to play the xylophone by watching the tutorial video after the break. [Humberto Evans] and the team at Nerd Kits do a great job of not only manufacturing the coils, but the xylophone itself. The bars are machined from some aluminum stock and they take you down the rabbit hole with they why’s and how’s of engineering the keys.

We’re unlikely to replicate this machining process but the solenoids are another story all together. Starting at about 3:30 you can learn about designing, building, and using these little marvels. They’re basically an electromagnetic cuff with a metal slug in the middle. The solenoid seen above uses a body milled from HDPE and wrapped with magnet wire. The slug in the center is steel, with a few rare-earth magnets at the top. When you run current through the coil it repulses the magnets on the slug, witch then strikes the xylophone key. Using a MOSFET and a protection diode, actuating them is as simple as sending a digital high from your microcontroller of choice.

We’ve seen solenoids used to play a vibrophone before, but those were commercial units. Making your own hardware is far more hardcore.

[Scott] built a confetti canon to spice up the party. It’s pneumatic and re-purposes a fire extinguisher as the air tank. He had a refillable extinguisher that used water instead of chemical retardant. After emptying the water and ensuring all of the pressure had been release he swapped the hose and nozzle for a sprinkler solenoid valve. Securing the extinguisher’s actuator lever with a pipe clamp holds the internal valve open, leaving the solenoid to control the pressure release. This way the canon can be fired electronically, or manually.

This type of solenoid valve is a popular choice with pneumatic canons. We suppose you could even adapt this for use as a T-shirt cannon.

[Thanks BoBeR182]

Okay, for many the fact that this typewriter plays Zork on paper instead of a CRT is the fascinating part of this hack. But we love the implementation that makes the keys of the device an input and output.

The electric typewriter has been fitted with a solenoid for each key (wow, that’s a lot of work). In the image above you can see they are housed on plywood platforms behind the typewriter and connect using a piece of mono-filament fishing line. This flexible connection means the solenoids have no adverse effect when you want to do the typing instead of the Arduino which drives the solenoids. [Johnathan M. Guberman] took advantage of this, adding a resistor for each key. When depressed the key completes a circuit with the resistor, acting as the input. In this way, you can play Zork with a piece of paper as the monitor, typing for the input, and watching the typewriter magically pound out responses. See it happen after the break.

[via Laughing Squid and Make]

[Doug] needed to update his watering system to comply with his city’s new water saving ordinance. The old system wasn’t capable of being programmed to water only on even or odd calendar days. Rather than purchase a replacement he decided to build his own sprinkler controller. It needed to switch 12V solenoids, a job that’s not too hard to design for. Rather than re-invent the wheel, he modified a previous controller design. It is basically an Arduino and Ethernet shield on a his own etched board. In addition to the ATmega328 and an ENC28J60 (for ethernet connectivity) there is a bank of transistors to drive the watering solenoids. Now he has a web interface that controls the watering schedule and is fully in compliance with the new city code.

If you need another way to save when watering your grass you should take a look at the sidewalk-avoiding sprinkler.

[Dan Kouba's] parents replaced their doorbell button with one that lights up and found that the chime wouldn’t stop sounding after the button was pushed. These lighted buttons use an incandescent bulb in parallel with the button (a piece of hardware we’ve hacked in the past). It draws a small amount of current which isn’t enough to trigger the chime, but it is just enough that the chime unit reacts as if the button press never stopped. His parents asked what he could do about this and after some investigation he build a replacement board for the chime unit based around an ATtiny26L. The board monitors the voltage drop across a resistor in the doorbell circuit. When the comparator on the AVR detects a rise in the voltage drop across the resistor it rings the chimes, actuating the solenoids with a set of PNP transistors. [Dan] sent us all of the details which you can check out after the break.

Dan writes:

My parents have this really old door mechanical chime that they got as a housewarming gift 25 years ago, and recently when they replaced the doorbell button with a newer lighted one, the bell wouldn’t stop chiming.  Apparently the light in the button passes enough current through it while its on (and the button is unpressed) that it triggers the bell over and over again.  They didn’t want to get rid of the doorbell, as the newer electronic ones just aren’t the same, so I was asked to see what I could do about it.  My solution was this project.

The old chime system consisted of a motor, which would be set into motion by pressing the button, and a set of contacts which the motor would revolve around and trigger the four solenoids that ring the chimes.  Once I disassembled it, the cause of the infinite cycle was obvious.  The motor’s start current was higher than the light in the bell would permit, but once it was triggered once by pressing the button, the bulb current was enough for it to remain in motion.  There wasn’t a whole lot I could do to fix the old system, so I designed a microcontroller based replacement.

I used an Attiny26L (admittedly overkill, but it was all I had on hand) for the brains of the operation, a button press detector made out of a comparator and a resistor (more about that in a second), and four transistors for triggering the solenoids.  Those parts along with the power supply (there was 20VAC available at the wall) fit onto a radioshack PCB which happened to fit perfectly where the old system had sat.  The old system had the option to either chime a sequence or only a single chime when the button was pressed, and I replicated this feature in software using the large blue DIP switch shown in the pictures.

My detector circuit is simply an 82 ohm 5W resistor inline with the button/light combo.  The button and the light are in parallel, so there is always some current passing through the line, causing a small voltage drop across the resistor.  When the button is pressed, the light is shorted out and the current becomes much higher, thus causing a higher voltage drop across the resistor.  I used a comparator attached to a voltage divider reference (half the supply) and to the resistor.  That in turn is connected to the AVR which monitors for the button press and triggers the chime accordingly.

One of the problems I ran into was that the solenoids are high side switched.  One lead of each solenoid is attached to the case, so unless I wanted to run 4 more wires, I had to use PNP transistors to switch them (I would have used MOSFETs, but I had the transistors in my parts box).  I used an NPN transistor to pull their bases low so switching from my 5V AVR was easier.

The code is really simple; it’s just an infinite loop watching the comparator output for a trigger, and after that it triggers either the chime sequence or the single chime based on the switch input.  I was originally going to use interrupts, but I had issued with multiple triggers.  The interrupt flag was cleared as soon as the ISR was being processed, so if the bell was pressed twice before the chime sequence was finished, the interrupt would trigger a second time once the ISR finished its first run.  A simple if…then statement fixed the problem.

Download [Dan's] code and schematic package.

There was a time when a drummer would grab some sticks and lay out a groove using the items around him as instruments. [Lsa Wilson] would rather not work quite that hard and has chosen to do the same thing by tapping on an iPhone screen. As you can see in the clip after the break, many of the items in the room around him have been fitted with solenoids. Each is connected to an Arduino which is then controlled by Open Sound Control and interfaced with the iPhone via TouchOSC. We love the sounds being created and can’t help being reminded of the Multixylophoniomnibus.

[Matt Meerian] introduced us to his kludge of cardboard, tape, mirrors, and electronics in the form of a clever non lethal robin trap. Whenever a pesky robin would enter the box, a sensor is triggered, the solenoid drops a lid, and the bird is contained (and we assume taken far away after that).

Of course the plan backfired; we wont spoil what happened, but you can click the link above to find out.

Related: Arduino Mouse Trap

We’re going to straight out agree with [Pete] on how surprisingly quiet doorbells are now a days, and if we had it our way we would put his Lunkenheimer train whistle doorbell in every home*. The setup he uses is surprisingly simple, opting for a pre-built wireless doorbell that signals a microcontroller which in turn drives a relay and solenoid. While he does include a video, we felt it didn’t quite show the intensity of these whistles.

*HaD is not responsible for hearing loss and subsequent melted brains.