Intro to Circuit Bending

Electronic musical instruments are a lot of fun for a hacker because, with a small palette of tools, know-how and curiosity, they are easily modified. As with any hack, there is always the chance that the subject will be ruined, so it’s not necessarily worth the risk to muck about inside your thousand-dollar pro synthesizer. Luckily for all of us, there are shovel-fulls of old electronic musical toys littering the curbs and second-hand shops of the world. These fun little devices provide ample opportunity to get familiar with audio electronics and circuit bending techniques.

A note on definitions: the term “circuit bending” can be synonymous with “hardware hacking” in the world of audio electronics, and we have seen some debate as to which term is better suited to a given project. We welcome you to share your viewpoints in the comments.

Keep reading to get started.
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Android Talks Pulsewave

Serial communications are a mainstay of digital computing. They don’t require much physical infrastructure and they exist in variations to fit almost any application. The behaviour of serial communications lines, varying from high to low voltage in a timed pattern, is analogous to a 1-bit DAC. Using a whole DAC for serial communication would be a waste in most cases, but the [RobotsEverywhere] team found an exception which you may have encountered already.

Since the audio output of the Android is accessible and addressable, [RobotsEverywhere] wrote source code to use the left and right channels as separate serial communication lines. This circumvents the need to bust into the device and muck about with the hardware which is great if you want a no-risk hack that allows communications to an RS232 port. Any hardware on which you can write to the DAC (and control the sampling rate) is a potential target.

There are some external electronics required to convert the audio signal to TTL, but it’s not very complicated–a couple of comparators and change. You can see it in action after the break.

As a bonus, when you’re done for the day you can plug in your headphones and listen to the soothing poetry of pulse waves all night long.

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PIC programmable power supply

This programmable power supply is the perfect addition to your bench tools. [Debraj Deb], who previously built a whole house power monitor, designed this build around a PIC 18F4520 microcontroller. The desired voltage is set with an attached keypad, resulting in a digital output on the 8-bits of port D. The port connects to another protoboard with an R-2R digital-to-analog converter resulting in the target voltage. A set of transistors amplifies the current and a power transistor then takes care of the final output. After the break you’ll find two videos, the first walks us through the hardware and the second demonstrates the device in action, along with measurements of its performance. This certainly provides a lot more functionality than an ATX power-supply conversion.

Update: A big thanks to [Debraj] who sent us a code package as well as the schematic (PDF) used during testing. We’re having trouble getting the code package up for download right now. Check back later, hopefully we’ll have it up soon.

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Atari 2600 recreated in an FPGA

Behold [Retromaster's] field programmable gate array implementation of an Atari 2600. The processor and video chip have both been built in the 100,000 gate Spartan-3E FPGA, with connectors for audio, video, and a Sega controller. The output signals are generated using two DACs made from R-2R resistor ladders, much like the project we saw in August. [Retromaster] included functionality for the system switches (difficulty and select) in the controller itself. There is VHDL code and board details available if you want to make one of your own. To help in making that decision we’ve embedded video of it after the break. [Read more...]

Building a discrete digital-analog-converter

Want to take back control of how your digital audio files become sound? One thing you can do is to build your own digital to analog converter. This one is made from discrete components, centered around a resistive ladder. Yes, there are a couple of integrated circuits in there which are used for demultiplexing the incoming signal but the magic happens in that R-2R network. The project is an interesting read and makes a point of looking at the issues raised when trying to precision match resistors. Apparently it can be done with 0.1% components if you have a lot of them and a multimeter that can measure down to seven decimal places.

[Thanks Bigbob]

One-handed GameCube controller

[Hasse] built a one-handed video game controller for his brother. He fit everything he needed into the body of an existing controller and came up with a very usable system. The controller will be right-hand only, so the left shoulder button was moved underneath the right side where your middle finger can get at it. This leaves the d-pad and the left analog stick to account for. By combining an ATtiny44A, an accelerometer, and a digital to analog converter the controller can sense motion. The microcontroller reads in the accelerometer data, gives user feedback via four added LEDs on the d-pad, and the DAC feeds the appropriate signals back into the controller as if you were using the stick. There is even a switch to select whether the motion data is mapped to the analog stick or to the d-pad. We’ve included a demo video after the break.

Find that you also need some one-armed typing assistance? Check out this half-qwerty keyboard hack. [Read more...]

Arduino based synthesizer

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[Jacob] is working on his final project for the Copenhagen Institute of Interaction Design.  Based around Arduino, the quality and quantity of his build notes make this a fascinating read and there are several examples to listen to.

The project features a brilliant idea for input:  He uses a 1/8″ TRS connector (mini-jack) whose tip is the input to the DAC of the Arduino. There are conductive pads in the shape of a keyboard that you touch the tip of the connector to in order to complete the circuit. Alternatively, the other two conductors on the connector deliver power and ground for easy interface with external controllers. He built an example controller that uses an LED and photoresistor to alter the signal returning to the Arduino. Put your hand in front of the light and the sound changes.

[via Arduino: blog]

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