April 2018 – Juvar's Electronics Corner

UART-controlled 7-segment display with Python GUI

This project uses this 7-segment display. It is based on Arduino. Display shows current gasoline price in Tampere, Finland. Gasoline price is middle price for 95E10 and it’s downloaded from www.polttoaine.net with Python code.

GUI (graphical user interface) is made with wxPython and wxFormBuilder. Update interval and serial port is user selectable.

Python code:

#! /usr/bin/python
# -*- coding: utf-8 -*-

import wx, wx.xrc
import threading
import serial
import urllib
from lxml.html import fromstring

class MyApp(wx.App):

    delay = 0
    runTime = 0

    def OnInit(self):
        self.res = wx.xrc.XmlResource("gui.xrc")
        self.frame = self.res.LoadFrame(None, "MyFrame1")
        self.text1 = wx.xrc.XRCCTRL(self.frame, "m_textCtrl1")
        self.text2 = wx.xrc.XRCCTRL(self.frame, "m_textCtrl2")
        self.slider1 = wx.xrc.XRCCTRL(self.frame, "m_slider1")
        self.frame.Bind(wx.EVT_BUTTON, self.on_evt_button, id=wx.xrc.XRCID("m_button1"))

        self.SetTopWindow(self.frame)
        self.frame.Show()
        
        self.delay = self.slider1.GetValue()*60
        self.updatePrice()
        self.thread = threading.Thread(target=self.delayTimer)
        self.thread.daemon = True
        self.thread.start()
        return True

    def on_evt_button(self, evt):
        self.delay = self.slider1.GetValue()*60

    def updatePrice(self):
        fopen = urllib.urlopen("https://www.polttoaine.net/Tampere")
        content = fopen.read()
        doc = fromstring(content)
        price = doc.find_class("Hinnat")[3].text_content()
        self.text1.SetValue(price)

        try:
            with serial.Serial(self.text2.GetValue(), 9600, timeout=1) as ser:
                time.sleep(5)
                ser.write(price+"\r")
        except IOError:
            print("Port cannot be opened")

    def delayTimer(self):
        self.runTime += 1
        if self.runTime >= self.delay:
            self.runTime = 0
            self.updatePrice()
        self.thread = threading.Timer(1,self.delayTimer)
        self.thread.daemon = True
        self.thread.start()       

app = MyApp(False)
app.MainLoop()

XRC layout file generated from wxFormBuilder:

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<resource xmlns="http://www.wxwindows.org/wxxrc" version="2.3.0.1">
  <object class="wxFrame" name="MyFrame1">
    <style>wxDEFAULT_FRAME_STYLE|wxTAB_TRAVERSAL</style>
    <size>380,165</size>
    <title>95E10 Gasoline Price Display</title>
    <centered>1</centered>
    <aui_managed>0</aui_managed>
    <object class="wxFlexGridSizer">
      <rows>3</rows>
      <cols>3</cols>
      <minsize>380,165</minsize>
      <vgap>0</vgap>
      <hgap>0</hgap>
      <growablecols></growablecols>
      <growablerows></growablerows>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_RIGHT|wxALIGN_CENTER_VERTICAL</flag>
        <border>5</border>
        <object class="wxStaticText" name="m_staticText1">
          <label>Current output</label>
          <wrap>-1</wrap>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_CENTER_HORIZONTAL|wxALIGN_CENTER_VERTICAL</flag>
        <border>5</border>
        <object class="wxTextCtrl" name="m_textCtrl1">
          <style>wxTE_READONLY</style>
          <value></value>
        </object>
      </object>
      <object class="spacer">
        <option>1</option>
        <flag>wxEXPAND</flag>
        <border>5</border>
        <size>0,0</size>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_RIGHT|wxALIGN_CENTER_VERTICAL</flag>
        <border>5</border>
        <object class="wxStaticText" name="m_staticText2">
          <label>Update interval (minutes)</label>
          <wrap>-1</wrap>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_BOTTOM|wxALIGN_CENTER_HORIZONTAL</flag>
        <border>5</border>
        <object class="wxSlider" name="m_slider1">
          <style>wxSL_HORIZONTAL|wxSL_LABELS</style>
          <size>100,-1</size>
          <value>30</value>
          <min>10</min>
          <max>120</max>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_CENTER_VERTICAL</flag>
        <border>5</border>
        <object class="wxButton" name="m_button1">
          <label>Save settings</label>
          <default>0</default>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_RIGHT|wxALIGN_CENTER_VERTICAL</flag>
        <border>5</border>
        <object class="wxStaticText" name="m_staticText3">
          <label>Serial port</label>
          <wrap>-1</wrap>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_CENTER_VERTICAL|wxALIGN_CENTER_HORIZONTAL</flag>
        <border>5</border>
        <object class="wxTextCtrl" name="m_textCtrl2">
          <value>/dev/ttyUSB0</value>
        </object>
      </object>
    </object>
  </object>
</resource>

Reading UART with Python GUI application

Finally, I can say that I can program in the Python language. I learned Python from this tutorial. It is a good combination of the languages that I previously knew (PHP, Javascript and SQL). Structure also reminds me of Delphi and Basic languages.

Here is a program that reads 1-wire temperature sensor DS18B20 and displays it’s value on GUI (graphical user interface). GUI is made with wxPython library and with wxFormBuilder software.

In between sensor and computer there is Arduino Nano which transforms data from 1-wire to UART.

Python code:

#! /usr/bin/python
# -*- coding: utf-8 -*-

import wx
import wx.xrc
import serial
from thread import start_new_thread

class MyApp(wx.App):

    def OnInit(self):
        self.res = wx.xrc.XmlResource("gui.xrc")
        self.frame = self.res.LoadFrame(None, "MyFrame1")
        self.text1 = wx.xrc.XRCCTRL(self.frame, "m_textCtrl1")
        self.text2 = wx.xrc.XRCCTRL(self.frame, "m_textCtrl2")
        self.button1 = wx.xrc.XRCCTRL(self.frame, "m_button1")
        self.frame.Bind(wx.EVT_BUTTON, self.on_evt_button, id=wx.xrc.XRCID("m_button1"))
        
        self.SetTopWindow(self.frame)
        self.frame.Show()
        return True

    def on_evt_button(self, evt):
        self.button1.SetLabel("Wait...")
        self.button1.Enable(False)
        start_new_thread(readSerial,(self,))

def readSerial(self):
    try:
        with serial.Serial(self.text2.GetValue(), 9600, timeout=1) as ser:
            line = ""
            while len(line) == 0:
                ser.write("\n")
                line = ser.readline()
            self.text1.SetValue(line.splitlines()[0] + u"°C")
    except IOError:
        print("Port cannot be opened")
    self.button1.Enable(True)
    self.button1.SetLabel("Read sensor")

app = MyApp(False)
app.MainLoop()

XRC layout file generated from wxFormBuilder:

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<resource xmlns="http://www.wxwindows.org/wxxrc" version="2.3.0.1">
  <object class="wxFrame" name="MyFrame1">
    <style>wxDEFAULT_FRAME_STYLE|wxTAB_TRAVERSAL</style>
    <size>-1,100</size>
    <title>1-Wire Temperature</title>
    <centered>1</centered>
    <aui_managed>0</aui_managed>
    <object class="wxGridSizer">
      <minsize>-1,100</minsize>
      <rows>2</rows>
      <cols>3</cols>
      <vgap>0</vgap>
      <hgap>0</hgap>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_CENTER_VERTICAL|wxALIGN_RIGHT</flag>
        <border>5</border>
        <object class="wxStaticText" name="m_staticText1">
          <label>Outdoor temp</label>
          <wrap>-1</wrap>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_CENTER_VERTICAL|wxALIGN_CENTER_HORIZONTAL</flag>
        <border>5</border>
        <object class="wxTextCtrl" name="m_textCtrl1">
          <style>wxTE_READONLY</style>
          <size>100,-1</size>
          <value>---</value>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_CENTER_VERTICAL</flag>
        <border>5</border>
        <object class="wxButton" name="m_button1">
          <label>Read sensor</label>
          <default>0</default>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_RIGHT|wxALIGN_CENTER_VERTICAL</flag>
        <border>5</border>
        <object class="wxStaticText" name="m_staticText2">
          <label>Port addr</label>
          <wrap>-1</wrap>
        </object>
      </object>
      <object class="sizeritem">
        <option>0</option>
        <flag>wxALL|wxALIGN_CENTER_VERTICAL|wxALIGN_CENTER_HORIZONTAL</flag>
        <border>5</border>
        <object class="wxTextCtrl" name="m_textCtrl2">
          <size>100,-1</size>
          <value>/dev/ttyUSB0</value>
        </object>
      </object>
    </object>
  </object>
</resource>

Arduino code:

#include <OneWire.h>
#include <DallasTemperature.h>

// Data wire is plugged into port 2 on the Arduino
#define ONE_WIRE_BUS 2

// Setup a oneWire instance to communicate with any OneWire devices
OneWire oneWire(ONE_WIRE_BUS);

// Pass our oneWire reference to Dallas Temperature. 
DallasTemperature sensors(&oneWire);

void setup(void) {
  Serial.begin(9600); // start serial port
  sensors.begin(); // Start up the library
}

void loop(void) { 
  while (Serial.available() > 0) { // if there's any serial available, read it
    if (Serial.read() == '\n') { // look for the newline
      sensors.requestTemperatures(); // Send the command to get temperatures
      Serial.println(sensors.getTempCByIndex(0)); // get temperature from first sensor only
    }
  }
}

Dual DC motor controller with Arduino

Two DC motor is independently controlled with Arduino Nano (Micro compatible) and with a dual H-bridge using PWM. Speed and direction is selectable with two potentiometers. Each potentiometer value is read with Arduino analog input. When potentiometer is on it’s center position then motor is off state.

Video: https://youtu.be/dS4pnsJSH2k

Arduino Nano and Micro contains three timers. Timer0 is used with Arduino internal commands so it leaves two timer (timer1 and timer2) to use with custom programs. Timer1 works with pins 9, 10 and timer2 works with pins 11 and 3.

Pulse width is selected with command analogWrite(pin, value). Analog input is read with command analogRead(pin). Code is below.

void setup() {
  pinMode(7, OUTPUT);
  pinMode(8, OUTPUT);
}

void loop() {
  
  int pot_1 = analogRead(1); // potentiometers values
  int pot_2 = analogRead(0);

// MOTOR ONE
  // direction backward
  if(pot_1 < 512-20) {
    digitalWrite(7,0); // motor direction
    int mot_1 = map(pot_1, 0, 512-20, 255, 0);
    analogWrite(10,mot_1);
  }
  // stop motor in middle position
  else if((pot_1 > 512-19) && (pot_1 < 512+19)) {
    digitalWrite(7,0); // motor direction
    analogWrite(10,0); // motor speed
  }
  // direction forward
  else if(pot_1 > 512+20) {
    digitalWrite(7,1); // motor direction
    int mot_1 = map(pot_1, 512+20, 1023, 255, 0);
    analogWrite(10,mot_1);
  }

// MOTOR TWO
  // direction backward
  if(pot_2 < 512-20) {
    digitalWrite(8,0); // motor direction
    int mot_2 = map(pot_2, 0, 512-20, 255, 0);
    analogWrite(11,mot_2);
  }
  // stop motor in middle position
  else if((pot_2 > 512-19) && (pot_2 < 512+19)) {
    digitalWrite(8,0); // motor direction
    analogWrite(11,0); // motor speed
  }
  // direction forward
  else if(pot_2 > 512+20) {
    digitalWrite(8,1); // motor direction
    int mot_2 = map(pot_2, 512+20, 1023, 255, 0);
    analogWrite(11,mot_2);
  }
}