The Artemis Synthesizer is a basic 12-bit resolution synthesizer which has an output sample rate of 22kHz. The output audio is filtered at 11kHz to satisfy Nyquist and prevent weird aliasing and reflections in the output audio. Internally the synthesizer generates sound using a predetermined wave table, which can be changed and recalculated if desired. By default, the wave table contains a sine wave with 256 steps, but harmonic sound data can be programmed into the synth kit using our web interface.
The synthesizer contains two interactive modes and one mode for the optical communication link. These modes are: a keyboard mode, which contains 4 scales (C major, C pentatonic, C blues and C minor) and has 8 available keys; and a sequencer mode, which can hold eight 8-step by 8-note sequences. In sequencer mode, new sequences can be entered from the web interface.
The optical link, which is kindly called the "Optoloader" has its own separate mode and detects timed transitions between black and white from a computer monitor. The light levels are taken in on a photo-transistor and transitions detected using an analogue comparator interrupt with the comparison set at V_bat/2. The data is encoded using BiPhase Mark Code which encodes the clock with the data. The link is generally reliable when the monitor is set to a high brightness and a low speed is used. Mostly it allows for us to have a kit which is interactive with minimal programming experience and can still be changed and played with long after they leave. Thus the web interface which was developed by Sam Damask becomes very important for the end goal of our project.
To interface between the digital and the analog we normally use something called a DAC (Digital to Analog Converter). There are a variety of different DACs. For example, there is the R-2R type DAC which is a ladder of resistors with digital inputs at different points. R-2R DACs are cheap, but are pin expensive; however, they can be extremely useful for reading off multiple switches or other such setup using the minimal number of microcontroller pins. For more on R-2R DACs see my write up on NOMIS, my Simon Clone.
For this application an R-2R DAC would be noisy and very difficult to get accurate readings off of. Instead I will be using a digital DAC IC from Microchip called the MCP4921, which has an SPI (Serial Peripheral Interface) bus.
For Boston University's Artemis Project the BU Electronic Design Facility (EDF) offers a two day session where we teach the students how to solder, solder up a kit and then do some embedded programming, traditionally on 8-bit AVR microcontrollers. Usually the project is a variation on the POV toy, which you see around online all of the time as a beginner electronics project. However, we decided to deviate from our traditional path this year and create our own synthesizer kit, with an SPI DAC, Audio Amplifier, Microcontroller and some buttons. There is also a possibility for programming in new wave forms via an optical link with a computer (post coming soon). To give a good overview of the whole project I plan on doing a write up on each part of the project as I go along.
First up lets check the constraints of our Audio Amplifier and see if we can get it working in an appropriate way. The amplifier we are using is a TDA2822M and is a dual audio amplifier. We are not driving a stereo channel, so we will be using the TDA2822M in a bridge configuration inorder to both push and pull on the speaker dramatically increasing the amount of power we can drive through the speaker.
From Friday, Jan 27 to Sunday, Jan 29 a few of my friends and I spent a lot of time at Artisan's Asylum in Somerville, MA. We weren't there just for fun (though we had plenty of fun). Instead we were there to design a working RC hovercraft in 48 hours. The participants from BUILDS (BU's hackerspace) were divided up into two teams:
Team McFly and the Hoverboard: Christopher Woodall (me), Ian Felder, Marc Beneck and Alejandro Bancalari
The Cult of the Devouring Fan and Brogle the Insatiable: Russel Shomberg, Patrick Ehrlicher, William Gullotta and Alex Whittemore
In the beginning we were given the electronics, a piece of pink foam, some wood and access to most of the tools in Artisan's Asylum. There is no real documentation from either my group's design, or the other BUILDS group's design; however we certainly had a ton of fun and we have pictures and videos. Also, it was my first time helping design a Radio Controlled vehicle and it was a ton of fun (which I hope to do again).
This is just a basic little dynamo which uses a tiny 6V DC motor I scavenged from an old CD drive. I have grander plans for the motor in the future, but I thought it would be cool to use it to turn on an LED with it!
The basic idea is pretty straight forward. If you take a motor, which has a permanent magnet in it, and turn the magnet on your own you will change the magnetic flux in the coil and as such start generating some current and, you will start to get a potential difference building up across the terminals of the motor. If I knew the RPM rating of the motor then I could figure out how fast to turn it to get a full 6 Volts. At the moment all I know is that I need to spin it pretty fast and the peak value my multimeter reads is 2.5 V, which is enough to power an LED.
Nomis is a Simon-like memory game for the ATTiny85, which uses the ATTiny85. The game logic in the ATTiny85 was implemented using AVR C and takes up 983 bytes in program memory and 6 bytes in data memory. The implementation size comes in under 1kB, but could most certainly be smaller. The pin usage, however, is very conservative and the games electronics take up a total of 4 of the 6 available pins. The 4 LEDs are controlled on 3 pins using Charlieplexing model (which could easily be extended to 6 LEDs). On the other hand the 4 pushbutton switches are feed into an ADC input through an R2R ladder configuration. I am very happy with the limited pin usage of this project.
The gameplay of Nomis is the same basic scheme as Simon. Which is to say once you initiate a game with it the game logic generates a random move, which lights up one of the 4 LEDs. Then Nomis waits for you to copy it. Each consecutive move is stored in an array and the string of moves must be copied exactly by the player. The game has no real ending conditions; however, the maximum number of moves is 100, but even then that limit was arbitrarily set by me. With a sufficiently large slice of memory and an extremely skilled (or cheat prone) individual the game could last forever. That said, the goal of the game is to best your previous score, which you keep track of by yourself.
I am putting together a color organ! Currently I do not have my schematics written up and I plan on making an in depth writeup when I get closer to being done. However, I did record a video of its current status!. I also have a photo dump on flickr.
The plan for the final project is to have the three filters (which need to be cleaned up), running into an RGB LED and controlling the different colors. I was thinking about shooting the produced light through a piece of sanded acrylic and try to get a nice effect that way.