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Digital Oscilloscope

A digital oscilloscope that displays the most important parameters

info

Author: Lazaroiu Mihai
GitHub Project Link: https://github.com/UPB-PMRust-Students/project-mihai1402

Description​

This project’s main function is to demonstrate the functionality of a digital oscilloscope programmed in Rust. The hardware consists of:

  • An analog pre-amplifier for preparing the input signal
  • A microcontroller for signal processing
  • A debugger to aid the microcontroller during testing
  • A screen for display

The software allows the hardware to perform various functions of an oscilloscope like displaying an external signal and measuring its key parameters.

Motivation​

I chose to build an oscilloscope,to combine my interest in electronics and audio signals with a practical and useful application. It also helps me understand theoretical concepts I've learned so far.

Architecture​

The hardware is composed of four main components:

  1. Pre-amplifier
    • Built using resistors, diodes, capacitors, and an op-amp in a non-inverting configuration.
  2. Processing unit
    • Based on the Raspberry Pi Pico 2 (main processor) and Raspberry Pi Pico H (debugger during testing).
  3. Display
    • Visualizes the signal from the microcontroller.
  4. Power supply
    • Feeds all the components with necessary voltage.

These 4 components work together to form the oscilloscope in the following way:

Signal flow:

  • Input signal → probe → pre-amplifier → ADC (Pico 2) → display.

Power setup:

  • Raspberry powered via USB; peripherals via 3.3V GPIO pin.

architecture

Log​

Week 10​

  • Wrote the documentation
  • Finished the pre-amplifier
  • Tested different screen types by drawing signal functions
  • Note: Final screen model still undecided, so specified crate is not yet final

Week 9​

  • Troubleshooting the pre-amplifier
  • Started more detailed software design

Week 8​

  • Started building the pre-amplifier

Week 7​

  • Parts arrived
  • Began planning next steps

Week 6​

  • Ordered parts for the pre-amplifier

Week 5​

  • Finished initial plan (hardware & software bill of materials)
  • Uploaded project idea document

Week 4​

  • Brainstormed project ideas

Hardware​

Components​

  • 5x Resistors (R1 → R5)
  • 5x Capacitors (C1 → C5)
  • 1x Diode (D1)
  • 1x Op-amp (MCP6002, non-inverting configuration)
  • Power source
  • Raspberry Pi Pico 2
  • Display
  • Probe

Function of Components​

  • C1: used to eliminate the DC component
  • R1, R2: form a voltage divider that ensures the input bias
  • R3, R4: are used to set the amplification factor of the op-amp to 1
  • C2: used so that the amplification only applies to the AC component
  • Op-amp: part of a MCP6002 integrated circuit that has 2 operational amplifiers. Only one of the 2 was used. A secondary function of the amplifier in combination with the voltage that powers it is to limit the max amplification in order to protect the internal ADC of the microcontroller
  • C3: used to make sure no DC component enters the ADC, after the operational-amplifier. C1 was used to block the DC component before the amplifier
  • C4: used to block high frequencies from generating auto-oscillations
  • C5: is used to eliminate spikes from a switching power supply
  • R5: limits potential high currents from affecting the ADC
  • D1: used to protect the non-inverting input of the amplifier from negative voltages
  • Probe: used to acquire the signal

Prototype Photos​

Breadboard analog pre-amplifier prototype:
Analog Preamp

Processing hardware:
Processing

Signal on screen:
Display Demo

Schematics​

The connections of the components described previously can be seen on the following electric diagram.

schematics

Bill of Materials​

DeviceUsagePrice
BNC Female ConnectorConnects the probe to the pre-amplifier5.83 RON
1N4148 DiodeProtects the non-inverting input of the op-amp0.49 RON
100kΩ Resistor (x2)Voltage divider and amplification factor0.10 RON
4µF Capacitor (x2)DC decoupling0.49 RON
MCP6002-I/P Op-AmpHigh input impedance operational amplifier3.00 RON
1.8kΩ ResistorAmplification factor setting0.05 RON
10nF CapacitorAvoid DC amplification0.10 RON
200Ω ResistorInput current limiting for ADC0.10 RON
Li-Ion 3.7V Battery 18650 (x2)Powers the oscilloscope32.00 RON
100nF CapacitorAvoid auto-oscillation0.10 RON
10µF CapacitorAvoid voltage spikes0.49 RON
Oscilloscope ProbeSignal acquisition79.99 RON
Raspberry Pi Pico 2Microcontroller unit (MPU)39.66 RON
Raspberry Pi Pico HDebugging42.74 RON
Display OLED 1.3" (Prototype)Shows signal and parameters20.99 RON
IC SocketSocket for op-amp1.37 RON
Header PinsConnects Raspberry Pico0.95 RON
Breadboard + Prototype Power SourcePrototyping circuit25.57 RON

Software​

LibraryDescriptionUsage
embassy-rpRaspberry Pi Pico 2 hardware abstractionUsed for interacting with peripherals like ADC, SPI, I2C, timers, and GPIOs to acquire and display waveform data
embassy-executorAsync task executor for embedded projectsManages concurrent tasks for waveform sampling, processing, and display update in real-time
embassy-timeTimekeeping and async timersUsed to generate accurate sampling intervals for the oscilloscope and trigger time-based actions
embassy-syncAsync-safe signals, mutexes, and channelsCoordinates data flow between ADC sampling, processing, and the display task to ensure smooth real-time updates
heaplessFixed-size data structures for no_stdImplements double buffering for waveform data to ensure no data loss during updates to the display
embedded-graphics2D graphics and text renderingRenders waveforms, signal properties like amplitude/frequency, and other graphical elements on the display
ssd1306Display driver for I2C OLED screensControls the OLED display to show real-time waveforms and signal information in the oscilloscope
display-interface-i2cAdapter crate for I2C display interfaceConnects the SSD1306 driver to the embedded-graphics library via I2C communication
microfftLightweight FFT crate for no_stdPerforms Fast Fourier Transform (FFT) to calculate the frequency of the signal in real time
cortex-mLow-level access to Cortex-M processor featuresSupports interrupts and system functions for handling ADC, DMA, and display updates
cortex-m-rtRuntime crate for Cortex-MInitializes the board and manages interrupt-driven tasks, including DMA and signal sampling
defmtLogging crate for embedded projectsProvides debug logging for signal data, task progress, and error tracking in the oscilloscope
panic-haltPanic handler for embedded projectsSafely halts the CPU on panic, ensuring stable operation in embedded systems like the oscilloscope
  1. Inspiration for the pre-amplifier
  2. Help for building the pre-amplifier