Make a digital audio oscilloscope
The Nanoscope Zero is a simple but functional digital oscilloscope using an Arduino Nano micro board. Darren Yates shows how to build it and explains how it works.
An oscilloscope is a must-have piece of test equipment to have on your workbench that helps you ‘see’ electrical signals in circuits. They can cost thousands of dollars, but to help explain how digital oscilloscopes work, we’ve developed the Nanoscope Zero using an Arduino Nano and OLED panel that you can make for little more than loose change.
BASIC SPECS
The Nanoscope Zero is an autotriggered, AC-coupled, single-channel oscilloscope with 64 kilo-samples per second (64kS/s) sample rate. It has a 128 x 64-pixel OLED panel with a simple graticule showing 1V per division vertically and 0.25 milliseconds per division horizontally. Its usable frequency range is up to 6kHz, it has a 1-kohm input impedance and a 5V peak-to-peak maximum input voltage range. These specs are pretty modest, particularly compared to something like Tektronix’s TBS2000, which captures one billion samples per second (1GSps) and has a 100MHz bandwidth. Nevertheless, Nanoscope Zero uses similar techniques to the big machines, albeit more modestly.
BUILDING THE SCOPE
You build Nanoscope Zero on a tiny 170-point breadboard using the Arduino Nano board, the OLED panel and a handful of passive components. Despite the breadboard, you will likely need to do some soldering for the input socket and possibly the DIP header pins for the Nano itself. Can’t solder? Rope in someone who can. Check the Parts List for the bits you’ll need. We purchased all of the major parts from eBay.
The input signal comes in via a 3.5mm stereo socket — feed it from the headphone socket of your phone or MP3 player. The two 470ohm resistors mix both left and right channels together to create a single input, which connects via a 10uF capacitor to the Nano’s A0 analog input pin. To ensure we get the maximum signal range possible, the A0 input is biased to half the supply voltage via two 10kohm resistors connected as a voltage-divider. The input socket is wired to three dupont wires, which then connect into the breadboard.
The OLED panel plugs into the breadboard via a 4-pin DIP header socket (make sure you get the 4-pin OLED panel) and we’re feeding power via wire links to analog inputs A6 and A7. We don’t use these inputs — simply the breadboard connections. This doesn’t blow the inputs up since the Nano keeps these inputs at high impedance when they’re not used.
HOW THE SCOPE WORKS
A digital oscilloscope takes an analog signal, converts it into digital samples and displays those samples in a graphlike form with voltage on the vertical or Y-axis and time on the horizontal or X-axis. This allows us to see voltage changes over time. But in terms of building a scope, the two key questions are how do we know a) the voltage scale, and b) the time period we’re looking at?