This is an additive synthesizer where you can change the timbre using a mixer made of merely pencil and paper. Why buy variable resisters when you can build one virtually for free?
Step 1: Parts List
Parts You’ll Need:
-3 alligator clips
-22 awg solid core wire
-7805, Voltage Regulator
-2 Synchronous 4-bit counters (74HC193N)
-4 1kΩ resistors
-1 1µF capacitor
-speaker and audio cable or headphones
-graphite pencil and paper
Step 2: BUILDING THE TIMER CIRCUIT
Put the 7555 on your breadboard. The 7555 is a timer and we will use it to drive the 4-bit counter. Connect pin 1* to ground. Connect pins 4 and 8 to voltage. Connect pin 2 to pin 6. Connect pin 1 to pin 2 via a 1µF capacitor. Connect pin 5 to voltage via a resistor. Connect pin 8 to pin 7 via a resistor and likewise pin 7 to pin 6, as shown.
Step 3: BUILDING THE 4-BIT COUNTERS
Place the 4-bit counter next to the 7555 on the board. Wire as shown. Connect the output of the timer (pin 3) to the input of the counter (pin 5). Pins 2, 3, 6 and 7 are the outputs that will go to the mixer.
Build another 4-bit counter the same way. Instead of connecting the input at pin 5 to the 7555, connect it to pin 7 of the previous counter. The yellow wires in the picture are running the output to a different spot on the board for easier access.
Step 4: BUILDING THE GRAPHITE MIXER
The most important part of this circuit is the simplest. Take your pencil and rub the graphite onto the paper making a thick, long rectangle. We want the graphite to conduct electricity, so make sure there are no lapses.
Connect one end of the graphite to the tip of the audio/headphone jack via an alligator clip. This is the red clip in the picture. Connect the other end to the breadboard’s ground (white clip). Connect the sleeve of the jack also to the breadboard’s ground (black clip). Connect the 8 outputs from the board to the mixer via long wires with exposed ends.
Step 5: POWERING THE CIRCUIT/GETTING SOUND
Make sure the ground rails are connected for common ground, and the voltage rails for common voltage. Connect the voltage regulator to the voltage rail and ground rail as shown. The voltage regulator converts 9V into 5V, which we need to power the circuit. To power up your circuit, connect a 9V battery as shown. Although it is not necessary, you may want to use an LED as an indicator for when the circuit is properly powered.
To get sound, make sure your mixer is connected to a speaker through the audio jack. If you don’t have this, headphones work just fine. You will have to press down on the wires so that the exposed tips connect with the graphite. The graphite acts as a variable resistor. By changing the wires position on the graphite, you change the amplitude of one of the components of the sound!