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

Back to top

MiniOscilloscope module

Schematic

BOM

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

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);
		}
	}
}

Back to top

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()

Back to top

Tests

Functional tests

Comparison USB and UART

Back to top