Low Cost, Audio Speed Digital Oscilloscope

By Morgan D. Jones

The goal of the project was to design a low-cost digital oscilloscope targeted at students, hobby-
ists, and researchers. The requirements of the oscilloscope were three-fold: 1) cost less than $100,
2) capture frequencies over the range 20Hz–20kHz, and 3) constructable with a basic soldering
iron and limited soldering skills. The primary parts of the oscilloscope are two Atmel ATmega644
microcontrollers, an Analog Device AD7825 ADC, and an NTSC television. One of the microcon-
trollers is used to generate an NTSC television signal, and the other is responsible for acquiring
and processing samples from the ADC.

The oscilloscope implements many of the same operations as a commercial oscilloscope. The
user can start/stop the display, arm a single sequence, adjust the time division, adjust the voltage
division, and adjust the trigger value. When the display is stopped, the user can also control a
cursor which has time and voltage readouts. The supported time divisions are 0.5ms–5s, and the
supported voltage divisions are 156mV–5V.

All the specified requirements were met satisfactorily. The total cost of parts required for the
oscilloscope was only $65.51, well within the specified budget. The oscilloscope can display signals
up to 40kHz with at least 10 samples per cycle, which is better than the requirement of 20Hz–20kHz.
Finally, the oscilloscope was designed entirely with parts that could be soldered by hand.

Full Report (PDF)

Source code (ZIP)

Board design (ZIP)

Character generator (ZIP)