Nandhopper 1-Bit Noise Synth

Step 3 Prototype: Make a Square Wave

NAND gates have two inputs and one output, and the 4093 has four NAND gates on it. Here's how they're connected. When both inputs are high, the output is low. In every other situation the output is high. The 4093 also has Schmitt triggers on its inputs, which helps make it resilient to noise and more likely to oscillate regularly.

There are a few ways to get a NAND gate to give you a square wave. We'll use a way that requires one gate, resistor, and capacitor per oscillator:

• Wire one input to high (9 V)
• Connect one input to ground via a capacitor
• Connect the output to the grounded input via a resistor

If you watch the output of this gate on an oscilloscope/listen, and switch out capacitor and resistor values, you'll notice you can approximate the frequency of the square wave by f = (1 / (r x c)). For example, when c = 470 pf and r = 10 megaohms, f = 212 Hz (measured at 250 Hz). This is where those numbers maximum resistance numbers come in handy for getting an idea of what kind of capacitance value to choose.

In short, if you use this circuit and change the resistance you can change the frequency. Furthermore, you can turn it on and off by wiring input 1 to ground instead of high.