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Tutorial – Arduino and Four Digit Seven Segment Display Module

This is a quick start guide for the Four Digit Seven Segment Display Module and Enclosure from PMD Way. This module offers a neat and bright display which is ideal for numeric or hexadecimal data. It can display the digits 0 to 9 including the decimal point, and the letters A to F. You can also control each segment individually if desired. 

Each module contains four 74HC595 shift registers – once of each controls a digit. If you carefully remove the back panel from the enclosure, you can see the pin connections:

four-digit-seven-segment-display-with-enclosure-from-pmdway

If you’re only using one display, use the group of pins at the centre-bottom of the board. From left to right the connections are:

  1. Data out (ignore for single display use)
  2. VCC – connect to a 3.3V or 5V supply
  3. GND – connect to your GND line
  4. SDI – data in – connect to the data out pin on your Arduino/other board
  5. LCK – latch – connect to the output pin on your Arduino or other board that will control the latch
  6. CLK – clock – connect to the output pin on your Arduino or other board that will control the clock signal

For the purposes of our Arduino tutorial, connect VCC to the 5V pin, GND to GND, SDI to D11, LCK to D13 and CLK to D12. 

If you are connecting more than one module, use the pins on the left- and right-hand side of the module. Start with the connections from your Arduino (etc) to the right-hand side, as this is where the DIN (data in) pin is located.

Then connect the pins on the left-hand side of the module to the right-hand side of the new module – and so forth. SDO (data out) will connect to the SDI (data in) – with the other pins being identical for connection. 

The module schematic is shown below:

four-digit-seven-segment-display-with-enclosure-from-pmdway

Arduino Example Sketch

Once you have made the connections to your Arduino as outlined above, upload the following sketch:

// Demonstration Arduino sketch for four digit, seven segment display with enclosure
// https://pmdway.com/collections/7-segment-numeric-leds/products/four-digit-seven-segment-display-module-and-enclosure
int latchPin = 13; // connect to LCK pin intclockPin = 12; // connect to CLK pin intdataPin = 11; // connect to SDI pin int LED_SEG_TAB[]={ 0xfc,0x60,0xda,0xf2,0x66,0xb6,0xbe,0xe0,0xfe,0xf6,0x01,0xee,0x3e,0x1a,0x7a,0x9e,0x8e,0x01,0x00}; //0 1 2 3 4 5 6 7 8 9 dp . a b c d e f off void setup() { //set pins to output so you can control the shift register pinMode(latchPin, OUTPUT); pinMode(clockPin, OUTPUT); pinMode(dataPin, OUTPUT); } void displayNumber(int value, boolean leadingZero) // break down "value" into digits and store in a,b,c,d { int a,b,c,d; a = value / 1000; value = value % 1000; b = value / 100; value = value % 100; c = value / 10; value = value % 10; d = value; if (leadingZero==false) // removing leading zeros { if (a==0 && b>0) { a = 18; } if (a==0 && b==0 && c>0) { a = 18; b = 18; } if (a==0 && b==0 && c==0) { a = 18; b = 18; c = 18; } if (a==0 && b==0 && c==0 && d==0) { a = 18; b = 18; c = 18; d = 18; } } digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[d]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[c]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[b]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[a]); digitalWrite(latchPin, HIGH); } void allOff() // turns off all segments { digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, LSBFIRST, 0); shiftOut(dataPin, clockPin, LSBFIRST, 0); shiftOut(dataPin, clockPin, LSBFIRST, 0); shiftOut(dataPin, clockPin, LSBFIRST, 0); digitalWrite(latchPin, HIGH); } void loop() { for (int z=900; z<=1100; z++) { displayNumber(z, false); delay(10); } delay(1000); for (int z=120; z>=0; --z) { displayNumber(z, true); delay(10); } delay(1000); digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[14]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[13]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[12]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[11]); digitalWrite(latchPin, HIGH); delay(1000); digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[16]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[15]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[14]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[13]); digitalWrite(latchPin, HIGH); delay(1000); digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[0]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[1]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[2]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[3]+1); digitalWrite(latchPin, HIGH); delay(1000); digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[7]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[6]+1); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[5]); shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[4]); digitalWrite(latchPin, HIGH); delay(1000); }

After a moment you should see the display spring into action in the same way as in the demonstration video:

How does it work? 

First we define which digital output pins are used for latch, clock and data on lines four to six. On line eight we have created an array which contains values that are sent to the shift registers in the module to display the possible digits and letters. For example, the first – 0xfc – will activate the segments to display a zero, 0x7a for the letter C, and so on. 

From line 20 we’ve created a custom function that is used to send a whole number between zero and 9999 to the display. To do so, simply use:

void displayNumber(value, true/false);

where value is the number to display (or variable containing the number) – and the second parameter of true or false. This controls whether you have a leading zero displayed – true for yes, false for no. 

For example, to display “0123” you would use:

displayNumber(123, true);

… which results with:

four-digit-seven-segment-display-with-enclosure-from-pmdway-0123

or to display “500” you would use:

displayNumber(500, false);

… which results with:

four-digit-seven-segment-display-with-enclosure-from-pmdway-500

To turn off all the digits, you need to send zeros to every bit in the shift register, and this is accomplished with the function in the sketch called 

allOff();

What about the decimal point? 

To turn on the decimal point for a particular digit, add 1 to the value being sent to a particular digit. Using the code from the demonstration sketch to display 87.65 you would use:

 digitalWrite(latchPin, LOW);

 shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[5]);

 shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[6]);

 shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[7]+1); // added one for decimal point

 shiftOut(dataPin, clockPin, LSBFIRST, LED_SEG_TAB[8]);

 digitalWrite(latchPin, HIGH);

… which results with:

four-digit-seven-segment-display-with-enclosure-from-pmdway-87p65

In-depth explanation of how the module is controlled

As shown in the schematic above, each digit is controlled by a 74HC595 shift register. Each shift register has eight digital outputs, each of which control an individual segment of each digit. So by sending four bytes of data (one byte = eight bits) you can control each segment of the display. 

Each digit’s segments are mapped as follows:

7segmentdisplaymap

And the outputs from each shift register match the order of segments from left to right. So outputs 0~7 match A~G then decimal point. 

For example, to create the number seven with a decimal point, you need to turn on segments A, B, C and DP – which match to the shift register’s outputs 0,1,2,8. 

Thus the byte to send to the shift register would be 0b11100001 (or 225 in decimal or 0xE1 in hexadecimal). 

Every time you want to change the display you need to re-draw all four (or more if more than one module is connected) digits – so four bytes of data are sent for each display change. The digits are addressed from right to left, so the first byte send is for the last digit – and the last byte is for the first digit. 

There are three stages of updating the display. 

  1. Set the LCK (latch) line low
  2. Shift out four bytes of data from your microcontroller
  3. Set the LCK (latch) line high

For example, using Arduino code we use:

  digitalWrite(latchPin, LOW);

  shiftOut(dataPin, clockPin, LSBFIRST, 0b10000000); // digit 4

  shiftOut(dataPin, clockPin, LSBFIRST, 0b01000000); // digit 3

  shiftOut(dataPin, clockPin, LSBFIRST, 0b00100000); // digit 2

  shiftOut(dataPin, clockPin, LSBFIRST, 0b00010001); // digit 1

  digitalWrite(latchPin, HIGH);

This would result with the following:

4digit7segmentdisplaymoduletronixlabsbits

Note how the bytes in binary match the map of the digits and their position. For example, the first byte sent was for the fourth digit, and the segment A was turned on. And that’s all there is to it – a neat and simple display. 

This post brought to you by pmdway.com – everything for makers and electronics enthusiasts, with free delivery worldwide.

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Tutorial – L298N Dual Motor Controller Modules and Arduino

Learn how to use inexpensive L298N motor control modules to drive DC and stepper motors with Arduino.

You don’t have to spend a lot of money to control motors with an Arduino or compatible board. After some hunting around we found a neat motor control module based on the L298N H-bridge IC that can allows you to control the speed and direction of two DC motors, or control one bipolar stepper motor with ease.

The L298N H-bridge module can be used with motors that have a voltage of between 5 and 35V DC. With the module used in this tutorial, there is also an onboard 5V regulator, so if your supply voltage is up to 12V you can also source 5V from the board.

So let’s get started!

L298N Dual Motor Controller Module 2A from PMD Way

First we’ll run through the connections, then explain how to control DC motors then a stepper motor. At this point, review the connections on the L298N H-bridge module.

Consider the following image – match the numbers against the list below the image:

L298N Dual Motor Controller Module 2A from PMD Way
  1. DC motor 1 “+” or stepper motor A+
  2. DC motor 1 “-” or stepper motor A-
  3. 12V jumper – remove this if using a supply voltage greater than 12V DC. This enables power to the onboard 5V regulator
  4. Connect your motor supply voltage here, maximum of 35V DC. Remove 12V jumper if >12V DC
  5. GND
  6. 5V output if 12V jumper in place, ideal for powering your Arduino (etc)
  7. DC motor 1 enable jumper. Leave this in place when using a stepper motor. Connect to PWM output for DC motor speed control.
  8. IN1
  9. IN2
  10. IN3
  11. IN4
  12. DC motor 2 enable jumper. Leave this in place when using a stepper motor. Connect to PWM output for DC motor speed control.
  13. DC motor 2 “+” or stepper motor B+
  14. DC motor 2 “-” or stepper motor B-

Controlling DC Motors

To control one or two DC motors is quite easy with the L298N H-bridge module. First connect each motor to the A and B connections on the L298N module. If you’re using two motors for a robot (etc) ensure that the polarity of the motors is the same on both inputs. Otherwise you may need to swap them over when you set both motors to forward and one goes backwards!

Next, connect your power supply – the positive to pin 4 on the module and negative/GND to pin 5. If you supply is up to 12V you can leave in the 12V jumper (point 3 in the image above) and 5V will be available from pin 6 on the module. This can be fed to your Arduino’s 5V pin to power it from the motors’ power supply. Don’t forget to connect Arduino GND to pin 5 on the module as well to complete the circuit.

Now you will need six digital output pins on your Arduino, two of which need to be PWM (pulse-width modulation) pins. PWM pins are denoted by the tilde (“~”) next to the pin number, for example:

Arduino UNO PWM pins

Finally, connect the Arduino digital output pins to the driver module. In our example we have two DC motors, so digital pins D9, D8, D7 and D6 will be connected to pins IN1, IN2, IN3 and IN4 respectively. Then connect D10 to module pin 7 (remove the jumper first) and D5 to module pin 12 (again, remove the jumper).

The motor direction is controlled by sending a HIGH or LOW signal to the drive for each motor (or channel). For example for motor one, a HIGH to IN1 and a LOW to IN2 will cause it to turn in one direction, and  a LOW and HIGH will cause it to turn in the other direction.

However the motors will not turn until a HIGH is set to the enable pin (7 for motor one, 12 for motor two). And they can be turned off with a LOW to the same pin(s). However if you need to control the speed of the motors, the PWM signal from the digital pin connected to the enable pin can take care of it.

This is what we’ve done with the DC motor demonstration sketch. Two DC motors and an Arduino Uno are connected as described above, along with an external power supply. Then enter and upload the following sketch:

// connect motor controller pins to Arduino digital pins
// motor one
int enA = 10;
int in1 = 9;
int in2 = 8;
// motor two
int enB = 5;
int in3 = 7;
int in4 = 6;
void setup()
{
  // set all the motor control pins to outputs
  pinMode(enA, OUTPUT);
  pinMode(enB, OUTPUT);
  pinMode(in1, OUTPUT);
  pinMode(in2, OUTPUT);
  pinMode(in3, OUTPUT);
  pinMode(in4, OUTPUT);
}
void demoOne()
{
  // this function will run the motors in both directions at a fixed speed
  // turn on motor A
  digitalWrite(in1, HIGH);
  digitalWrite(in2, LOW);
  // set speed to 200 out of possible range 0~255
  analogWrite(enA, 200);
  // turn on motor B
  digitalWrite(in3, HIGH);
  digitalWrite(in4, LOW);
  // set speed to 200 out of possible range 0~255
  analogWrite(enB, 200);
  delay(2000);
  // now change motor directions
  digitalWrite(in1, LOW);
  digitalWrite(in2, HIGH);  
  digitalWrite(in3, LOW);
  digitalWrite(in4, HIGH); 
  delay(2000);
  // now turn off motors
  digitalWrite(in1, LOW);
  digitalWrite(in2, LOW);  
  digitalWrite(in3, LOW);
  digitalWrite(in4, LOW);
}
void demoTwo()
{
  // this function will run the motors across the range of possible speeds
  // note that maximum speed is determined by the motor itself and the operating voltage
  // the PWM values sent by analogWrite() are fractions of the maximum speed possible 
  // by your hardware
  // turn on motors
  digitalWrite(in1, LOW);
  digitalWrite(in2, HIGH);  
  digitalWrite(in3, LOW);
  digitalWrite(in4, HIGH); 
  // accelerate from zero to maximum speed
  for (int i = 0; i < 256; i++)
  {
    analogWrite(enA, i);
    analogWrite(enB, i);
    delay(20);
  } 
  // decelerate from maximum speed to zero
  for (int i = 255; i >= 0; --i)
  {
    analogWrite(enA, i);
    analogWrite(enB, i);
    delay(20);
  } 
  // now turn off motors
  digitalWrite(in1, LOW);
  digitalWrite(in2, LOW);  
  digitalWrite(in3, LOW);
  digitalWrite(in4, LOW);  
}
void loop()
{
  demoOne();
  delay(1000);
  demoTwo();
  delay(1000);
}

So what’s happening in that sketch? In the function demoOne() we turn the motors on and run them at a PWM value of 200. This is not a speed value, instead power is applied for 200/255 of an amount of time at once.

Then after a moment the motors operate in the reverse direction (see how we changed the HIGHs and LOWs in thedigitalWrite() functions?).

To get an idea of the range of speed possible of your hardware, we run through the entire PWM range in the function demoTwo() which turns the motors on and them runs through PWM values zero to 255 and back to zero with the two for loops.

Controlling a Stepper Motor

Stepper motors may appear to be complex, but nothing could be further than the truth. In this example we control a typical NEMA-17 stepper motor that has four wires:

stepper motor from PMD Way

It has 200 steps per revolution, and can operate at at 60 RPM. If you don’t already have the step and speed value for your motor, find out now and you will need it for the sketch.

The key to successful stepper motor control is identifying the wires – that is which one is which. You will need to determine the A+, A-, B+ and B- wires. With our example motor these are red, green, yellow and blue. Now let’s get the wiring done.

Connect the A+, A-, B+ and B- wires from the stepper motor to the module connections 1, 2, 13 and 14 respectively. Place the jumpers included with the L298N module over the pairs at module points 7 and 12. Then connect the power supply as required to points 4 (positive) and 5 (negative/GND).

Once again if your stepper motor’s power supply is less than 12V, fit the jumper to the module at point 3 which gives you a neat 5V power supply for your Arduino.

Next, connect L298N module pins IN1, IN2, IN3 and IN4 to Arduino digital pins D8, D9, D10 and D11 respectively. Finally, connect Arduino GND to point 5 on the module, and Arduino 5V to point 6 if sourcing 5V from the module.

Controlling the stepper motor from your sketches is very simple, thanks to the Stepper Arduino library included with the Arduino IDE as standard.

To demonstrate your motor, simply load the stepper_oneRevolution sketch that is included with the Stepper library, for example:

L298N Dual Motor Controller Module 2A from PMD Way

Finally, check the value for

	const int stepsPerRevolution = 200;

in the sketch and change the 200 to the number of steps per revolution for your stepper motor, and also the speed which is preset to 60 RPM in the following line:

	myStepper.setSpeed(60);

Now you can save and upload the sketch, which will send your stepper motor around one revolution, then back again. This is achieved with the function

	myStepper.step(stepsPerRevolution); // for clockwise
	myStepper.step(-stepsPerRevolution); // for anti-clockwise

So there you have it, an easy an inexpensive way to control motors with your Arduino or compatible board.

This post brought to you by pmdway.com everything for makers and electronics enthusiasts, with free delivery worldwide.

To keep up to date with new posts at tronixstuff.com, please subscribe to the mailing list in the box on the right, or follow us on twitter @tronixstuff.

Tutorial – PCF8574 backpacks for LCD modules and Arduino

Learn how to use inexpensive serial backpacks with character LCD modules with your Arduino.

Introduction

Using LCD modules with your Arduino is popular, however the amount of wiring requires time and patience to wire it up correctly – and also uses a lot of digital output pins. That’s why we love these serial backpack modules – they’re fitted to the back of your LCD module and allows connection to your Arduino (or other development board) with only four wires – power, GND, data and clock.

You can use this with LCD modules that have a HD44780-compatible interface with various screen sizes. For example a 16 x 2 module:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

The backpack can also be used with 20 x 4 LCDs. The key is that your LCD must have the interface pads in a single row of sixteen, so it matches the pins on the backpack – for example:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

Hardware Setup

Now let’s get started. First you need to solder the backpack to your LCD module. While your soldering iron is warming up, check that the backpack pins are straight and fit in the LCD module, for example:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

Then solder in the first pin, while keeping the backpack flush with the LCD:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

If it’s a bit crooked, you can reheat the solder and straighten it up again. Once you’re satisfied with the alignment, solder in the rest of the pins:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

Now to keep things neat, trim off the excess header pins:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

Once you’ve finished trimming the header pins, get four male to female jumper wires and connect the LCD module to your Arduino as shown in the following image and table. Then connect your Arduino to the computer via USB:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way
16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

Software Setup

The next step is to download and install the Arduino I2C LCD library for use with the backpack. First of all, rename the “LiquidCrystal” library folder in your Arduino libraries folder. We do this just to keep it as a backup.

If you’re not sure where your library folder can be found – it’s usually in your sketchbook folder, whose location can usually be found in the Arduino IDE preferences menu:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

Next, visit https://bitbucket.org/fmalpartida/new-liquidcrysta… and download the latest file, currently we’re using v1.2.1. Expanding the downloaded .zip file will reveal a new “LiquidCrystal” folder – copy this into your Arduino libraries folder.

Now restart the Arduino IDE if it was already running – or open it now. To test the module we have a demonstration sketch prepared, simply copy and upload the following sketch:

/* Demonstration sketch for PCF8574T I2C LCD Backpack 
Uses library from https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads GNU General Public License, version 3 (GPL-3.0) */
#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C	lcd(0x27,2,1,0,4,5,6,7); // 0x27 is the I2C bus address for an unmodified backpack

void setup()
{
  // activate LCD module
  lcd.begin (16,2); // for 16 x 2 LCD module
  lcd.setBacklightPin(3,POSITIVE);
  lcd.setBacklight(HIGH);
}

void loop()
{
  lcd.home (); // set cursor to 0,0
  lcd.print(" tronixlabs.com"); 
  lcd.setCursor (0,1);        // go to start of 2nd line
  lcd.print(millis());
  delay(1000);
  lcd.setBacklight(LOW);      // Backlight off
  delay(250);
  lcd.setBacklight(HIGH);     // Backlight on
  delay(1000);
}

After a few moments the LCD will be initialised and start to display our URL and the value for millis, then blink the backlight off and on.

If the text isn’t clear, or you just see white blocks – try adjusting the contrast using the potentiometer on the back of the module.

How to control the backpack in your sketch

As opposed to using the LCD module without the backpack, there’s a few extra lines of code to include in your sketches. To review these, open the example sketch mentioned earlier.

You will need the libraries as shown in lines 3, 4 and 5 – and initialise the module as shown in line 7. Note that the default I2C bus address is 0x27 – and the first parameter in the LiquidCrystal_I2C function.

Finally the three lines used in void setup() are also required to initialise the LCD. If you’re using a 20×4 LCD module, change the parameters in the lcd.begin() function.

From this point you can use all the standard LiquidCrystal functions such as lcd.setCursor() to move the cursor and lcd.write() to display text or variables as normal. The backlight can also be turned on and off with lcd.setBacklight(HIGH) or lcd.setBacklight(LOW).

You can permanently turn off the backlight by removing the physical jumper on the back of the module.

Changing the I2C bus address

If you want to use more than one module, or have another device on the I2C bus with address 0x27 then you’ll need to change the address used on the module. There are eight options to choose from, and these are selected by soldering over one or more of the following spots:

16 x 2 character LCD (white text blue background) with parallel interface from PMD Way

There are eight possible combinations, and these are described in Table 4 of the PCF8574 data sheet which can be downloaded from the NXP website. If you’re unsure about the bus address used by the module, simply connect it to your Arduino as described earlier and run the I2C scanner sketch from the Arduino playground.

This post brought to you by pmdway.com everything for makers and electronics enthusiasts, with free delivery worldwide.

To keep up to date with new posts at tronixstuff.com, please subscribe to the mailing list in the box on the right, or follow us on twitter @tronixstuff.