Audio output selection courtesy of the Internet

[Peter] was tired of crawling behind his desktop computer to switch between headphones and speakers. We feel his pain, as the headphone port on our computer speakers has its own demonic hum rendering the jack useless to us. His solution was to build this output selector board, then control it via the network.

A relay is responsible for routing the single input to one of two outputs. One output is wired to the normally closed pin on the relay, the other to the normally open pin. The important thing here is to make sure you have a separate audio ground so as not to pick up noise from the rest of the hardware.

What you see above is only the switching circuitry. This is where [Peter] went a little overboard, using an Arduino along with an Ethernet shield to drive the relay via a transistor. For this particular application there must be an easier way. But if you’re working on home automation from your smart phone, this might be just the thing to make your audio setup browser-controlled.

[via Build Lounge]

Inkjet print head driver shield

[Nicolas C Lewis] is churning out inkjet print head shield kits for Arduino. If you’ve always wanted to label or brand objects as part of a project this greatly simplifies the process. Using his all through-hole design, an Arduino can print at 96 dpi. At first we had trouble figuring out what we could use this concept for, but [Nicolas] has the answer. In is FAQ he links to a couple of his own flat-bed inkjet printer builds based on earlier prototypes, but he also links to other projects using the same concepts like the Nickel-O-Matic, or the ping-pong ball printer (we’ve embedded video of that one after the break).

The shield only requires five connections with a microcontroller. We love the jumper-based connection system that [Nicolas] chose which lets you use several print heads at once by selecting different drive pins. The project is still in the funding stage but is already over funded. Schematic and code will be posted as soon as the first production run is complete.

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A Stackable Motor Driver Shield for the Arduino

The Arduino has been used for many purposes, and  “shields” are available to make many common tasks easier.  However, [Nick] wanted a stackable motor driver shield, so he build one himself!. There are many motor driver shields available for the Arduino, however, there aren’t any that allow one to drive as many motors as were needed for his project, and none that were stackable.

[Nick] had no experience designing and fabricating a custom board, but decided to try his hand at it anyway. Armed with a free version of [Eagle] PCB design software, he designed the board that he needed then sent it to [Seeed] to be manufactured. According to his article, a quantity of 10 Arduino-sized boards can be purchased for the price of $25. At that price point, some hobbyists may want to consider this option rather than manually creating their own circuit.

According to [Nick], he was able to manufacture his first board with no errors on his first run! Not bad for his first try at something like this.

DTMF shield aimed at ham controlled Arduino

[Colin] wanted a way to reliably control an Arduino via ham radio. One of the easiest methods of automated radio control makes use of Dual-Tone Multi-Frequency signalling. To those who aren’t into amatuer radio you probably recognized DTMF as the touch-tone system for telephone communications. [Colin] built a shield that has an audio input and can decode DTMF signals.

The hardware is based around an MT8870 DTMF decoder chip. This is a popular choice for DTMF hardware because it does all of the decoding work for you. Whenever a valid tone is detected it outputs the associated value in binary on four output pins. There is a fifth pin that strobes after each new tone. [Colin’s] design offers a lot of feedback for what’s going on with the input signal. The DTMF value is displayed on a 7-segment display (controlled completely in hardware), the value is output on for Binary Coded Decimal pins, and mapped to a set of ten pins which pull to ground to match the digit received.

Going cellular with your Arduino projects

You can add a huge measure of extensibiltiy to a project by using a cellular connection. Anywhere the device can get service you can interact with it. In the past this has been a pretty deep slog through datasheets to get everything working, but this tutorial will show the basics of interacting with phone calls and text messages. It’s the 26th installment of what is becoming and mammoth Arduino series, and the first one in a set that works with the SM5100B cellular shield.

We love the words of warning at the top of the article which mention that a bit of bad code in your sketch could end up sending out a barrage of text messages, potentially costing you a bundle. But there’s plenty of details and if you follow along each step of the way we think you’ll come out fairly confident that you know what you’re doing. Just promise us that you won’t go out and steal SIM cards to use with your next project. Find part two of the tutorial here and keep your eyes open for future installments.

AVR HV Rescue Shield 2

[Jeff Keyzer] has a new version of the HV Rescue Shield available. This tool allows you to use an Arduino to reset the fuse bits on AVR microcontrollers. This is necessary if you make a mistake and disable the reset pin, or choose the incorrect clock settings (this will probably happen to you at some point). In order to bring the chip back to life you’ll need to use High Voltage Programming. The last version of the shield only worked with High Voltage Parallel Programming (HVPP) but this rendition can also use High Voltage Serial Programming (HVSP) for 8-pin chips that don’t have enough inputs for parallel communications.

As we talked about in our AVR Programming Tutorials this is no replacement for a high-end programmer like the STK500 or an AVR Dragon, but if you already have an Arduino a kit will only cost you $20 (or you can etch and build it yourself). We would have liked to see a breakout header for the HVP signals for off-board use. The absence of a breakout header doesn’t preclude this, but since you need the on board boost converter for the 12V signals, and because this shield can’t be used with a breadboard due to pin spacing, it’s hard to patch into signals for non-DIP use. We also think some clever firmware hacking and this could be used for HV programming, like we needed for that LED light bulb.

Homemade music player

Sadly, this pocket mp3 wav player doesn’t come close to the capabilities of even an iPod generation 1 yet, but you have to give [Owen] props for making it in less than 24 hours. The system consists of a Propeller MCU (cleverly wired to be swappable with “shields” similar to Arduino systems), SD card for song storage, and an LM386 for audio. While the setup is a little dull, and only plays through songs non stop with no controls whatsoever, it certainly is a good start in the right direction for a cheap and simple portable music player. Of course some planned changes are in the works, include an accelerometer (gesture based controls?), etched PCB, docking station, and a case. We’re surprised there is no form of screen planned, considering Owen appears to have a rather good handle on touch interfaces; perhaps he’s waiting for revision 3.