MiniOscilloscope

Design and implementation of a miniature oscilloscope module with a usb interface. The main use of the module is monitoring the signals SPI and I2C interfaces. The repository is a patchwork of files that makes entire project. More accurate information about the project can be found in the ./docs/ (unfortunately Polish language)

Project of the MiniOscilloscope includes:

• PCB design and assembly,
• program for XMEAGA 32A4-AU microcontroller written in C,
• GUI run on PC written in Python,
• system tests.

Table of Contents

1. Requirements
2. System architecture
3. MiniOscilloscope module
   • Schematic
   • BOM
   • PCB design
   • Microcontroller program
4. User application
5. Tests
   • Functional tests
   • Comparison USB and UART

Requirements

Acquisition parameters:

• time resolution of at least 15 samples per clock cycle (SPI / I2C)
• 8bit voltage resolution
• input voltage range 0 - 3.3V
• two channels
• trigger signal input
• trigger mode: normal

Parameters of the printed circuit:

• minimum sizes
• two-layer
• elements on one side of PCB
• possibility of manual PCB assembly

Electrical parameters:

• power supply from USB
• surge protection

User application:

• displays observed signals in real time
• allows you to manipulate presented graph
• allows you to stop/start acquisition Other:
• minimal construction cost
• data transmission to PC using the USB interface
• test signal output

System architecture

<p align="center"> <img src="images/architecture.png" width="500"> </p>

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MiniOscilloscope module

Schematic

<p align="center"> <img src="images/schematic.png" width="700"> </p>

BOM

<p align="center"> <img src="images/bom.png" width="700"> </p>

PCB design

The PCB was designed in accordance with the assumptions set in Requirements paragraph. Parameters of the printed circuit:

• dimensions: 22 x 32 mm,
• two-layer circuit,
• min track width: 8 mil
• min space between tracks: 6 mil
• min hole: 0.45 mm
• min border: 11 mil
• descriptions: TOP layer

<p align="center"> <img src="images/pcb.png" width="700"> </p>

Microcontroller program

Complete source code in ./source/Xmega/

int main(void)
{
	sysclk_init();
	pmic_init();
	adc_init();
	dma_init();
	evsys_init();
	tc_init();
	ioport_init();
	
	ioport_set_pin_dir(IO_TRIGGER, IOPORT_DIR_INPUT);
	ioport_set_pin_mode(IO_TRIGGER, IOPORT_MODE_PULLUP);
	ioport_set_pin_dir(IO_CTRL_LED, IOPORT_DIR_OUTPUT);
	
	cpu_irq_enable();
	adc_enable(&ADCA);
	pwm_enable();
	udc_start();
	
	while (1)
	{
		while(!udi_cdc_getc());
		while (0 == ioport_get_pin_level(IO_TRIGGER));
		while (1 == ioport_get_pin_level(IO_TRIGGER));
		
		dma_channel_enable(DMA_CHANNEL_0);
		dma_channel_enable(DMA_CHANNEL_1);

		if (udi_cdc_is_tx_ready())
		{
			while(dma_channel_is_busy(DMA_CHANNEL_1));
			udi_cdc_write_buf(&buffer_samples, RAM_BUFFER_SIZE_2000);
			ioport_toggle_pin_level(IO_CTRL_LED);
		}
	}
}

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User application

Complete source code in ./source/Gui/

from Gui import *
import serial

SAMPLES_NR=1000
CHANNEL_NR=2

serial_port = serial.Serial(port = 'COM3', write_timeout=0.1, inter_byte_timeout=0.1)
serial_port.flushInput()
RTS= bytearray(b'\xff')

gui=GUI(CHANNEL_NR,SAMPLES_NR)
paused = False

while True:

    key  = gui.get_key()
    if key == ' ':
        paused = not paused
        gui.toggle_state()
    elif key  == 'escape':
        break

    if not paused:
        try:
            serial_port.flushInput()
            serial_port.write(RTS)
            for channel in range(CHANNEL_NR):
                buffer = serial_port.read(SAMPLES_NR)
                gui.set_y(channel, buffer)
        except:
            pass

    gui.plot()
    gui.pause()

<p align="center"> <img src="images/gui.png" width="700"> </p>

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Tests

Functional tests

<p align="center"> <img src="images/functional.png" width="700"> </p>

Comparison USB and UART

<p align="center"> <img src="images/usb_uart_test.png" width="700"> </p>

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