Arduino-Simple-DSO

This DSO needs only a standard Arduino-Uno or Arduino-Nano, a HC-05 Bluetooth module or a micro USB OTG cable / adapter, a few resistors and capacitators and this software.

               

Simple DSO with no attenuator on breadboard	DSO Chart screen

The application is also available as an example of the Arduino BlueDisplay library - use File -> Examples -> Examples from Custom Libraries. You can load the library with Tools -> Manage Libraries... or Ctrl+Shift+I. Use "BlueDisplay" as filter string.

Features

• 150 kSamples per second with good quality.

• 300 kSamples per second with acceptable quality because of internal ADC limitations.

• Full touch screen control of all parameters.

• AC Measurement supported by using (passive) external attenuator circuit (see below).

• Automatic trigger level, range and offset selection.

• Manual trigger level and range select.

• Trigger delay.

• External trigger.

• 1120 byte data buffer - 3.5 times display size.

• Display of min, max, average and peak to peak values.

• Display of period and frequency.

• 3 different types of external attenuator, detected by software.

  • no attenuator (pin 8+9 left open).
  • passive attenuator with /1, /10, /100 attenuation (pin 8 connected to ground).
  • active attenuator (pin 9 connected to ground) - still experimental.

• Using 1.1 volt internal reference. 5 V (VCC) is also selectable and is useful if no attenuator is attached.

• Integrated frequency generator using 16 bit Timer1. Frequency from 119 mHz (8.388 second) to 8 MHz

• Integrated PWM Waveform generator for sinus, triangle and sawtooth using 16 bit Timer1. Frequency from 1.9 mHz to 7.8 kHz

Bill of material

1. Arduino Nano
2. Breadboard 400 points
3. Resistors
   • Resistors for the simple (0-5 V) version: 1x 10 kΩ, 2x 100 k, 1x 4 M or more.
   • Resistors for the 3 range (0-110 V) version: 1x 2.2 kΩ, 2x 10 k, 3x 100 k, 2x 220 k, 2x 1 M, 1x 4 M or greater
4. Capacitors
   • Capacitors for the simple version: 1x 100 nF / 10 V (or more)
   • Capacitors for the 3 range (0-110 V) version: 4x 100 nF / 100 V (or more), 6.8 µF
5. Jumper wires

Optional for Bluetooth connection 6. HC-05 Bluetooth module 7. Schottky diode e.g. BAT42

INSTRUCTIONS FOR USE

The DSO software has 4 pages.

1. The start page which shows all the hidden buttons available at the chart page.
2. The chart page which shows the data and info line(s).
3. The settings page.
4. The frequency generator page.

CHART PAGE

DSO Chart analyze screen	DSO Chart analyze screen with long info

Here you see the current data. This page has two modes, the acquisition (measurement running) and the analyze (data stored) mode. The horizontal violet line is the trigger level line and the two light green lines in analyze mode are the maximum and minimum level lines. On this page you can:

• Start and stop a measurement.
• Start a single one time measurement (Singleshot).
• Toggle the history mode.
• Go to the settings page.
• Change timebase by horizontal swiping in acquisition mode.
• Scroll through the 3 screen data buffer by horizontal swiping in analyze mode.
• If manual range selection enabled, change the range by vertical swiping.
• Change the info display from short to long to no info by short touching on the display. See below for info display reference.
• Display the hidden buttons by doing a long touch.
• Touch the light yellow vertical bar at the left to enable the voltage picker line (which is drawn destructive).
• If enabled, trigger value can be set by touching the light violet vertical bar in the 4. left grid. If switching info mode, the chart content will be restored.

SHORT INFO LINE REFERENCE

• Arithmetic-average and peak to peak voltage of actual chart (In analyze mode, chart is longer than the display!)
• Frequency
• Timebase for div (31 pixel)

LONG INFO LINE REFERENCE

First line

• Timebase for div (31 pixel)
• Slope of trigger
• Input channel: (0-5), T->AVR-temperature, R->1.1 volt-internal-reference G->internal-ground
• Minimum, arithmetic-average, max and peak to peak voltage of actual chart (In hold mode, chart is longer than display!)
• Trigger level
• Reference used: 5=5 volt, 1=1.1 volt-internal-reference

Second line

• Frequency
• Period
• first interval (pulse for slope ascending)
• second interval (pause for slope ascending)

SETTINGS PAGE GUI

DSO settings menu	DSO frequency / waveform generator menu

On this page you have all buttons to modify the DSO acquisition mode, to select the different ADC channels and for page navigation above the last button row the minimum stack size, the supply voltage and the internal chip temperature is shown. The stack size is required for testing different buffer size values during development and the temperature may be quite inaccurate.

• History -> red history off, green history on, i.e. old chart data is not deleted, it stays as a light green trace. This button is also available (invisible) at the chart page.

• Slope - Slope A -> trigger on ascending slope, Slope D -> trigger on descending slope.

• Back -> Back to chart page.

• Trigger delay -> Trigger delay can be numerical specified from 4 µs to 64.000.000 µs (64 seconds, if you really want). Microseconds resolution is used for values below 64.000.

• Trigger - the trigger value can be set on the chart page by touching the light violet vertical bar in the 4. left grid.

  • Trigger auto -> let the DSO compute the trigger value using the average of the last measurement.
  • Trigger man timeout -> use manual trigger value, but with timeout, i.e. if trigger condition not met, new data is shown after timeout. This is not really a manual trigger level mode, but it helps to find the right trigger value. -Trigger man -> use manual trigger value, but without timeout, i.e. if trigger condition not met, no new data is shown. -Trigger free means free running trigger, i.e. trigger condition is always met. -Trigger ext uses pin 2 as external trigger source.

• Input selector

  • %1 -> Pin A0 with no attenuator, only a 10 kΩ protection resistor.
  • %10 -> Pin A1 with an 1 to 10 attenuator.
  • %100 -> Pin A2 with an 1 to 100 attenuator.
  • CH 3 -> sequences through the channels CH 4, Temp (internal temperature sensor), VRef (internal reference).

• Frequency Generator -> go to frequency generator page.

• Range - There a 3 ranges, 0-2.5 , 0-5 and 0-10 volt

  • Range auto -> let the DSO choose the range based on the minimum and maximum values of the last measurement.
  • Range man -> select the range by vertical swiping on the chart page.

• Offset

  • Offset 0V -> Range starts at 0 volt.
  • Offset auto -> For small signals with a high DC offset. If range is not the lowest one and the signal has a DC offset, then a lower range is choosen and the display offset is adapted to show the complete signal
  • Offset man

• DC / AC

  • Since the internal ADC converter has only a DC input, AC offsets the inputs DC value to 1/2 reference using Arduino pin A5 and compensates this offset for the display. Therefore you must apply the signal using a capacitor!

• Reference voltage

  • Ref 1.1V (recommended if having attenuators) -> uses the internal 1.1 volt reference for the ADC.
  • Ref VCC -> uses VCC (5 volt supply) as reference for the ADC.

TOUCH

Short touch switches info output, long touch shows active GUI elements.

Waveform PWM output

Maximum values	Minimum values
SINE: clip to minimum 8 samples per period => 128 µs / 7812.5 Hz	7,421 mHz
SAWTOOTH: clip to minimum 16 samples per period => 256 µs / 3906.25 Hz	3.725 mHz
TRIANGLE: clip to minimum 32 samples per period => 512 µs / 1953.125 Hz	1.866 mHz

RC-Filter suggestions

• Simple: 2.2 kΩ and 100 nF
• 2nd order (good for sine and triangle): 1 kΩ and 100 nF -> 4.7 kΩ and 22 nF
• 2nd order (better for sawtooth): 1 kΩ and 22 nF -> 4.7 kΩ and 4.7 nF

Do not run DSO acquisition and non square wave waveform generation at the same time. Because of the interrupts at 62 kHz rate, DSO is almost not usable during non square wave waveform generation and waveform frequency is not stable and decreased, since not all TIMER1 OVERFLOW interrupts are handled.

SCREENSHOTS

DSO start screen	DSO at work
DSO chart screen	DSO chart screen with long info

Linearity of the ATmega328P(B) ADC converter

The captured signal was generated with a STM32F303 DAC and the DSO input range was chosen to see the LSB of the 10 bit ADC conversion.

All ranges including the 1 ms range (up to 30 kSamples per second / 26 µs conversion time) have almost perfect linearity.	In the 50 µs to 10 µs ranges with 300 kSamples per second (3 µs conversion time) the linearity is only acceptable.
First small linearity issues can be seen in the 496 µs range with 60 kSamples per second (13 µs conversion time).	And in the 101 µs range with 150 kSamples per second (6.5 µs conversion time).

SCHEMATICS

SIMPLE 1 RANGE VERSION	3 RANGE VERSION

Revision History

Version 3.3 - 02/2023

• Compatible to new BlueDisplay library version.

Version 3.2 - 11/2019

• Clear data buffer at start and at switching inputs.
• Multiline button caption.

Version 3.1

• Stop response improved for fast mode.
• Value computation for ultra fast modes fixed.
• millis() timer compensation formula fixed.
• AC/DC button and info line handling improved.