Instructables

Analog Beat Box

Picture of Analog Beat Box
This is an analog circuit that plays a synthesized drum beat. It can be scaled in amount and the quality of the noises.  
 
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Step 1: What You Need

Picture of What You Need
1 power source
3 breadboards
Wires (Yellow, Blue, Red, and Other) if you feel like following conventions
2 Speakers
6 OPA551 Op-Amps
2 TL081 Op-Amps
4 2N3904 NPN Transistors
2 10kOhm potentiometers
2 diodes
2 LEDs (optional)
Resistors:
3 200kOhm
6 1kOhm
2 4.4kOhm
1 3.7kOhm
3 1.7kOhm
2 160kOhm
3 5.8kOhm
Capacitors:
4 0.1uF
2 0.047uF

An Oscilloscope for debugging can come in quite useful.
Wire stripper/cutter

Step 2: The Circuit

Picture of The Circuit
It all goes together just like this. It's good to note that we only included a "bass" and a "snare". Prepare a circuit diagram of any other tones you wish to include in your circuit if you wish to add additional sounds on top of the basic ones we've included.

Step 3: Making the Beat

Picture of Making the Beat
This circuit uses a hysteretic oscillator as origin of the "beat". The hysteretic oscillator in this circuit has a frequency of about 1 hertz. The oscillator outputs a capacitor voltage "shark wave" which is compared using a comparator circuit to a steady voltage of about 2.5 volts. The 2.5 volts is made simply from a power source and a series of resistors. When the shark wave exceeds with the steady voltage, the comparator outputs 12 volts, essentially turning the circuit "on". When the shark wave is below the steady voltage, the comparator outputs 0 volts, essentially turning the circuit "off". For the second part of the beat, another comparator is used but compares the shark wave to -2.5 volts is used and that triggers in a similar fashion to the previous.
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