murisdaq

Read and plot serial data from a microcontroller

MurisDAQ displays serial data in real time. It is intended as a simple way to plot data from a microcontroller. It may not very efficient in the way resources are used, as it just repeatedly reads ascii from the serial port printed line-by-line by the microcontroller, but it helps to quickly evaluate microcontroller-acquired data values with minimal effort.

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Contents

1. Requirements
2. Usage
   1. Example 1: Plot data from Raspberry Pico in real time
   2. Example 2: Plot more than one signal
   3. Example 3: Arduino example
   4. Example 4: Plot y vs x
3. Settings

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Requirements

• PyQt6
• NumPy
• PyQtGraph
• pySerial

Usage

1. Connect your microcontroller to the "master" computer. Set up the microcontroller to send data over the serial port (typically with print or printf; see examples below).

2. Run python murisdaq.py on the "master" computer.

3. Open Settings and set baud rate and port if necessary.

4. Click the "play" button to display the data.

5. Click the "record" button to save the data to the default directory (as set in the settings dialog). The file name will be made up of the current date and time. The file format will be plain text (space-separated if more than one column).

Example 1: Sample analog data and plot in real time (Micropython)

A light-dependent resistor (aka photoresistor) was connected to a Raspberry Pico (adc pin 26) in order to measure the relative intensity of ambient light. The following micropython code was set to read and print the measured voltage every 500 ms:

from machine import ADC
import utime

conversion_factor = 3.3/(2**16-1)

# Light-dependent resistor
ldr = ADC(26)

while True:
    ldr_adc_val = ldr.read_u16()
    ldr_voltage = ldr_adc_val * conversion_factor
    print(ldr_voltage)
    utime.sleep_ms(500)

Running python murisdaq.py on the "master" computer and clicking the "play" button shows in real time the data. In this example the y-axis units are volts (as established in the micropython code above when adc values are converted to voltage before printing).

Example 2: Plot more than one signal

More that one signal can be plotted simultaneously by just setting the microcontroller to print more than one value as needed. In this example, one (analog) thermometer was connected to adc pin 28 on the same Raspberry Pico as above. The micropython code is now:

from machine import ADC
import utime

conversion_factor = 3.3/(2**16-1)

# Light-dependent resistor
ldr = ADC(26)

# Thermometer (TPM37, analog)
tmp37 = ADC(28)

while True:
    tmp37_adc_val = tmp37.read_u16()
    tmp37_voltage = tmp37_adc_val * conversion_factor
    tmp37_temperature = tmp37_voltage/0.02

    ldr_adc_val = ldr.read_u16()
    ldr_voltage = ldr_adc_val * conversion_factor

    print(tmp37_temperature, ldr_voltage)

    utime.sleep_ms(500)

MurisDAQ will detect and plot the two signals. In this figure, the top trace is the ambient temperature (in degrees C) and the bottom trace is the relative ambient light intensity (in volts):

Example 3: Using with Arduino

To test on an Arduino, the following code was uploaded to an Arduino Uno (using Arduino IDE). The Arduino generates two fake signals; these values must be printed on the same line, separated by a space:

void setup() {
  Serial.begin(9600);
}

float value = 0;
int direction = 1;
const float interval = 0.1;

void loop() {
  Serial.print(value);  // Print the first value
  Serial.print(' ');  // Print a space to separate the values
  Serial.println(sin(value));  // Print the second value and end the line
  value += (interval * direction);
  if ((value < -PI) | (value > PI)) {
    direction *= -1;
  }
  delay(50); // in ms
}

(This same code works for any other microcontroller that can be programmed with the Arduino IDE, e.g. Adafruit Feather.)

After setting the correct baud rate and serial port in the settings dialog MurisDAQ plots the two "signals" in real time:

Example 4: Plotting y vs x

In all the examples above the data sampled lacks time information: the y values are plotted against the index of the sample. To plot the sampled values instead against time it is possible to set up the microcontroller to print timer data and use this value in MurisDAQ. To illustrate this, following from Example 2 a thermometer was connected to a Raspberry Pico (adc pin 28). With the micropython code below the temperature is read every second and printed to serial. This time, however, timer information (ticks in milliseconds) are also printed (this must always be this first value in print()):

from machine import ADC
import utime

conversion_factor = 3.3/(2**16-1)

# Thermometer (TPM37, analog)
tmp37 = ADC(28)

while True:
    now = utime.ticks_ms()
    tmp37_adc_val = tmp37.read_u16()
    tmp37_voltage = tmp37_adc_val * conversion_factor
    tmp37_temperature = tmp37_voltage/0.02

    print(now, tmp37_temperature)

    utime.sleep(1)

MurisDAQ will plot both sets of data -- timer (in ms) and temperature (in deg C) -- as two signals:

But this is not what we want here: we want the first signal to be used as x values. That is achieved by opening the Settings dialog and checking First signal is time under Plot settings. Now the temperature is plotted against time:

Settings

Serial settings

Select your microcontroller's baud rate and port. Pressing the port refresh button will scan for devices connected ot the serial port. Thus, you can connect/disconnect microcontrollers without having to restart MurisDAQ.

Saving settings

This sets the directory where all data will be saved. The files will be named according to their date and time of creation.

Plot settings

Window width sets the width of the plot in number of samples; i.e. a window width of 500 means that the most recent 500 samples will be displayed in real time. Values older than that are discarded from the view.

Line colour opens a colour selection dialog to choose the colour of the plotted curve(s).

First signal is time, if checked, the first signal in the data will not be plotted. Instead, this will be taken to be x and thus used to plot the rest of the data samples against these values; see Example 4.