For the project, you will construct an analog synthesizer module to expand our existing modular system. You will be allowed to use existing schematics you find from the web and elsewhere. I will allow you to work in groups of up to three people; although there will be benefit to splitting up the work such as having one person build the circuit on the breadboard while another starts inputting the schematic into Eagle, please try to have everyone involved at least a little bit with every aspect of the process. Projects with two people should be larger in scope than projects with one person; projects with three people should have even larger scope. (I will often use the word “team” to refer to “teams” of just one person as well as two or three people, so don’t let that confuse you.) I will help you scope your project accordingly. If two people independently come up with similar project ideas, I may suggest that they join forces.
You could “modularize” part of a complete synthesizer circuit (i.e. build a module based on the VCO, VCF, or whatever of a subcircuit of a complete synthesizer). This may involve adding/modifying input and output circuitry so that the resulting module matches the specifications given below, and also may involve “updating” the circuit to use modern parts. It would be nice if this was relatively “original,” in that a modularized version doesn’t already obviously exist on the web.
I’m allowing you to make such extensive use of existing designs since (a) most of the synth
designers I know of actually got their start from tinkering around and modifying older designs, and (b) even getting a circuit from a published schematic working can be challenging.
If you would prefer, you can do something more original. If you’re doing a project that is based less on existing proven designs, I will put priority on helping you out during the design process. However, given the size of the class this semester, the amount of time I have to spend with each team will be less than what I had in the past, so my general tendency will be to steer you towards projects that I am pretty confident you could get working. Far-out experimentation could be fun, but we don’t really have enough time remaining in the semester to be too ambitious.
You must be sure to give credit to the original inspirations of your designs wherever possible.
Your module must either make audio (i.e. an oscillator), or process audio (i.e. a filter or nonlinear waveshaper), or sometimes both (i.e. a filter that self-resonates when the Q is turned up really high). Since this will be a component of a synthesizer, in general, some aspect of your module should be controllable via a control voltage; for instance, a filter whose cutoff is solely controlled by a pot won’t do.
Here is an extensive list of project ideas. You shouldn’t by any means feel restricted to pick something on that list (which I’ll keep adding to as random ideas strike me); you can use the list to get an idea of the sort of things I’m looking for.
Collaboration policy: Teams are strongly encouraged to help other teams out, both with bantering around design ideas and particularly with debugging. Often, the mere act of trying to explain what’s on the breadboard to someone else will cause you to discover the source of a bug. You can draft people from outside the class to help you design and debug too. Feel free solicit advice on online forums (the SDIY list that I’m going to make you join will be particularly helpful.) The only caveat on all this is that you must thank the people who aided you and describe how they aided you in your report. (Also, don’t be dishonest about it, i.e. don’t try to con someone online into designing an entire circuit for you.)
Timeline: How about the following rough timeline:
- By Monday, March 26, send me an e-mail about what you want to do for your project and who you are working with. (If you have absolutely no clue, I’ll try to suggest something, but I’d prefer if people picked something they’re enthusiastic about). I want to have a diversity of projects, so if someone tells me they want to do a project someone has already picked, I’ll probably suggest they try something else (or suggest some additional twist), or possibly suggest they join forces. Project topics are first come, first serve, more or less. Put “ACMS project idea” in your e-mail header so I can easily sort through them. The sooner you get this to me, the better; I have an encyclopedic knowledge of obscure synthesizer related esoterica (you may have noticed), and I can probably suggest some ideas to to give you a head-start. I will get together with you and give you whatever parts you need.
- Depending on your project, it would be a good idea for you to get me a draft schematic as soon as possible – you can scan it and e-mail it to me. I may put it on a website and post it to the SDIY mailing list to get comments and suggestions. If you’re modularizing or modifying an existing design, you can print out the schematic and kind of sketch out the changes you are planning to make, or just send me a URL to the schematic and describe the changes you plan to make in an e-mail.
- By Monday, April 2, have your circuit assembled on the breadboard.
- By Monday, April 9, let’s have a fully debugged and refined design on the breadboard. Debugging circuits is tricky; it requires a detective’s mind! There may be a problem in the hookup on the breadboard, or there may be a problem with the underlying design in the schematic, and you never know which is the case at first.
- By Monday, April 16, have a PCB layout of your circuit design ready for fabrication. I will help you with the PCB layout. If you do the schematic capture in Eagle (you can download the free-to-use version), I will be able to refine your PCB design. (Your first several PCB layouts are guaranteed to be pretty bad; it takes a lot of practice. If needed, I can meet with you and explain to you what I’m changing and why I’m changing it so you can pick up tips and tricks on the things I sort of do subconsciously.)
- Sometime during the weekend of April 28-April 29 — show me a working, soldered module. (You’ll probably discover errors on your PCB; you may “hack” these however you need to get them going.) That weekend, all the senior design students will have largely cleared out and we will have the labs to ourselves.
Documentation: In addition to the project, I want a brief user’s manual (in electronic form, e-mailed to me) explaining what your module is, what the controls do, etc., and a few basic notes about how you came up with the design, any calculations you made (for instance, to get something to match the MOTM standards), etc. Please include photos of your final built circuit board. (Including a photo of the breadboarded version would be nice, but is optional.) Basically, your report should be sufficiently detailed for someone else to reproduce your work. This should be reasonably slick, i.e. the text should not be handwritten. I’d like to emphasize the word “brief.” I am more interested in PRODUCT than I am in PROSE. Do not write something lengthy, since I will not have time to read it anyway. Please get this to me sometime during the week of April 30 to May 4, ie. finals week.
Due dates, sort of: The above timeline is just a guideline to help you gauge your progress; I won’t be carrying a specific checkoff list. (However, if you start falling behind these guidelines, you should redouble your efforts to catch up.)
Specifications: Your module should satisfy the MOTM standards (taken from the MOTM website):
- 1/4″ jacks for connections (I have a bunch of 1/4″ jacks)
- In general, a 1 volt-per-octave response for VCOs and filters (you may want to include an additional linear input, if appropriate). Some filter designs won’t have a clear exponential control mechanism; don’t feel obligated to try to add one.
- When running wires to the jacks, use black for ground (this will make debugging easier).
- Positive-going GATE voltages (+1.5 V threshold)
- Positive-going triggers
- Audio levels of 10 V peak-to-peak (i.e., -5 V to +5 V)
- VCAs respond from 0 to +5 volts
- Use the standard MOTM power connectors. There’s two kinds, depending on what you need. If the long tab is to the “right,” then reading from top to bottom, the MOTM power supply gives -15 V DC, two ground pins, and +15 V DC. (The MOTM website says these are “standard AMP MTA-156 4 position” connectors.) If you are using some digital logic (TTL, CMOS, whatever), you can use the six-pin connector. The bottom four pins are the same as the for the four-pin connector, and the topmost pin gives +5 V DC and a “digital ground” (so you can try to keep digital switching noise away from the “analog” part of your circuit.) The ECE lab staff stocks these; ask in the stockroom.
Parts: I have some specialized parts, particularly the LM13700. If you want something to experiment with or put in your final design, just ask. A lot of more standard parts, including pots and TL08x type op amps (which are a good workhorse audio op amp) are available form the ECE lab stockroom. If you need some other part that I don’t currently have, let me know and I’ll see if I can get it.
Tips on jacks: Some jacks we are using allow connections to be “normalled,” which may come in handy in your design. If you look at the jacks, you will see that ground is ground, but the signal connection can go to one or two points. When you plug in a cord, the signal part of the plug will connect to the “signal” part of the jack. But if you don’t plug anything in, the signal part of the plug will snap to a “default” connection.
In lab, you can use the various signal generators to provide audio, and you can use the many speakers hooked to the computers in the lab to listen to the audio. It is often convenient to clip allegator clips directly to the jacks themselves to emulate plugging something in.
Grading: Your project grade will be based on how impressed I am.
I consider the project to be the most important thing in the class; hence, your course grade will max out at whatever your project grade is, e.g., if you do B work in the exams and homeworks but turn in an A project, you might get an A for the class, or you might get a B; but if you do A work on everything else but turn in B level project, your grade won’t be an A.
My general procedure in this class is to push each student until I see what I consider “A” level work.