Lab 1/22

This is your first formal lab assignment.  It will be graded using the good old ‘check’ system.

0 = you didn’t show up
check – = incomplete
check = complete (at least parts 1-3).
check + = you did something awesome, above and beyond what was required
check ++ = you did something *really* awesome

You will be working for the most part in groups of three.  *If you look at the assignment and know how to build it immediately…awesome.  Help someone else figure out how to do it, without resorting to doing it yourself.*

This lab is divided into a series of smaller parts.

Part 1: Making Sound (5-10 min)
Get sound from an external sound source playing through a driver.


  • A sound source – like music on your computer or phone
  • An MD0105 LM4889 audio amplifier breakout board
  • An 8 ohm speaker driver – the 0.2 watt drivers will do
  • An audio plug/jack combo to get sound from speaker to the AIN (audio in pin)
  • A variable DC power supply (wall wart) and dc board-mount jack
  • A breadboard
  • Some wires/alligator clips

1. Put together your MD0105 audio amp.  You will need to solder this component — have someone on your team who is comfortable doing this put it together, but watch and learn for next time.

On the left side:
AIN is short for audio in, and will be the signal for your audio source.
SHD is a special power-saving feature on this amp – don’t worry about it.
5V is where you will plug in the + side power source.
Ground is where you will plug in the – side of your power source.

On the right side:
Orient the blue mini pot with the numbers as shown in the diagram.  This controls the volume.
The two leads for the speaker will go to the speaker pins-polarity doesn’t matter.

2. Next up, you’ll want to get power into your breadboard.  Plug your variable power supply into the dc board mount jack, and into an AC power supply.  Set it to 4.5V. Test with a multimeter to find the +/- pins and plug in your amp, + to 5V and – to GND.

3. Hook up your audio signal.  This is a mono amp, so you will only be able to hook up one channel of audio.  You will need to hook up the signal (tip) to AIN and the ground (sleeve) to GND.

4. Hook up your driver.  You should have sound.  Turn the pot to make it louder/softer.

Assuming everything went well, unplug your power and move to part 2.

Part 2: Make an audible, light-sensitive, pitch-variable oscillator from an inverter (or ‘Not Gate’)


  • 74HC14N Hex Schmitt Inverter (do a google search to find datasheet)
  • 0.1 uF capacitor (and a few other sizes/types)
  • A few different sizes of variable photoresistors
  • Breadboard
  • Variable power supply and dc board-mount plug
  • Hookup wire
  • Your amplifier and driver from the first part of the lab

Make some noise, as per the instructions above.  Note that we are no longer using the audio from your laptop/phone.  All sound is being synthesized from scratch.  I am not including a circuit diagram at this point, to give you the opportunity to work out the problem independently.

Part 3: Make five more of the same, all on this one chip, outputting to a single amp.


  • Everything from part 2
  • At least 5 more capacitors and 5 more photoresistors of different sizes.
  • 6 10kOhm resistors (or anything from 3kOhm to 1 mOhm, as long as they are all the same)

At this point you should be ‘tuning’ your system…experiment with different capacitor/photoresistor combinations to get a set of ranges that work together, for your group.  Test each individually to make sure they all work, before hooking them up together.

Part 4: Create polyphony.

  • Find a simple method for giving some of these different ‘voices’ more independence.  It should also make for a intuitive/fun interaction in ‘playing’ the instrument.

Part 5: Practice, refine, perform, and draw your circuit diagram.  

  • In any remaining time, experiment with different techniques for playing the noise machine, making any refinements to the system, and come up with a 30 – 60 second demo piece. Ideally you will all play a part in the performance.
  • At this point, it’s also worth drawing your circuit diagram.  Draw just one oscillator, and be able to explain how it works.

Part 6: Make something else.

  • The above assignment is a very basic circuit, chosen to get you up and running.  We have an abbreviated lab today, but in the event you have time left over, try making something more interesting.  It could build on what you’ve done so far, or be something entirely new.  If you’re looking for another easy project, try making your own metronome.  If you’re looking to tackle a bigger project, (perhaps not so much in the remaining time…) check out ‘Music from Outer Space‘.

Part 7: Clean-up

  • Be sure to leave enough time to clean up before 2 pm.  By 2 pm we should be basking in the glorious etherwaves of the theremin.

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