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Tutorial – Arduino and MC14489 LED Display Driver

Learn how to use MC14489 LED display driver ICs with Arduino in chapter fifty-one of a series originally titled “Getting Started/Moving Forward with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.

Updated 12/05/2013

Introduction

Recently we’ve been looking at alternatives to the MAX7219 LED display driver IC due to pricing and availability issues (stay tuned for that one) – and came across an old but still quite useful IC – the MC14489 from Motorola (now Freescale Semiconductor). The MC14489 can drive five seven-segment LED numbers with decimal point, or a combination of numbers and separate LEDs. You can also daisy-chain more than one to drive more digits, and it’s controlled with a simple serial data-clock method in the same way as a 74HC595 shift register. Sourcing the MC14489 isn’t too difficult – it’s available from element14, Newark, Digikey, and so on – or if you’re not in a hurry, try the usual suspects like Futurlec.

For the purpose of the tutorial we’ll show you how to send commands easily from your Arduino or compatible board to control a five-digit 7-segment LED display module – and the instructions are quite simple so they should translate easily to other platforms. Once you have mastered the single module, using more than one MC14489 will be just as easy. So let’s get started.

Hardware

Before moving forward, download the data sheet (pdf). You will need to refer to this as you build the circuit(s). And here’s our subject in real life:

mc14489

For our demonstration display we’ll be using a vintage HP 5082-7415 LED display module. However you can use almost any 7-segment modules as long as they’re common-cathode – for example, Sparkfun part number COM-11405. If you’re using a four-digit module and want an extra digit, you can add another single digit display. If you want a ruler, the design files are here.

Connecting the MC14489 to an LED display isn’t complex at all. From the data sheet consider Figure 9:

schematic

Each of the anode control pins from the MC14489 connect to the matching anodes on your display module, and the BANK1~5 pins connect to the matching digit cathode pins on the display module. You can find the MC14489 pin assignments on page 1 of the data sheet. Seeing as this is chapter fifty-one  – by now you should be confident with finding such information on the data sheets, so I will be encouraging you to do a little more of the work.

Interesting point – you don’t need current-limiting resistors. However you do need the resistor Rx – this controls the current flow to each LED segment. But which value to use? You need to find out the forward current of your LED display (for example 20 mA) then check Figure 7 on page 7 of the data sheet:

currentgraph

To be conservative I’m using a value of 2k0 for Rx, however you can choose your own based on the data sheet for your display and the graph above.  Next – connect the data, clock and enable pins of the MC14489 to three Arduino digital pints – for our example we’re using 5, 6 and 7 for data, clock and enable respectively. Then it’s just 5V and GND to Arduino 5V and GND – and put a 0.1uF capacitor between 5V and GND. Before moving on double-check the connections – especially between the MC14489 and the LED display.

Controlling the MC14489

To control the display we need to send data to two registers in the MC14489 – the configuration register  (one byte) and the display register (three bytes). See page 9 of the data sheet for the overview. The MC14489 will understand that if we send out one byte of data it is to send it the configuration register, and if it receives three bytes of data to send it to the display register. To keep things simple we’ll only worry about the first bit (C0) in the configuration register – this turns the display outputs on or off. To do this, use the following:

and to turn it off, send bit C0 as zero. The small delay is necessary after each command.

Once you have turned the display on – the next step is to send three bytes of data which represent the numbers to display and decimal points if necessary. Review the table on page 8 of the data sheet. See how they have the binary nibble values for the digits in the third column. Thankfully the nibble for each digit is the binary value for that digit. Furthermore you might want to set the decimal point – that is set using three bits in the first nibble of the three bytes (go back to page 9 and see the display register). Finally you can halve the brightness by setting the very first bit to zero (or one for full brightness).

As an example for that – if you want to display 5.4321 the three bytes of data to send in binary will be:

Let’s break that down. The first bit is 1 for full brightness, then the next three bits (101) turn on the decimal point for BANK5 (the left-most digit). Then you have five nibbles of data, one for each of the digits from left to right. So there’s binary for 5, then four, then three, then two, then one.

To demonstrate everything described so far, it’s been neatly packaged into our first example sketch:

… with the results in the following video:


Now that we can display numbers and a few letters with binary, life would be easier if there was a way to take a number and just send it to the display.

So consider the following function that takes an integer between 0 and 99999, does the work and sends it to the display:

So how does that work? First it splits the 5-digit number into separate digits and stores them in the array numbers[]. It then places the fourth digit into a byte, then moves the data four bits to the left – then we bitwise OR the fifth digit into the same byte. This leaves us with a byte of data containing the nibbles for the fourth and fifth digit. The process is repeated for digits 2 and 3. Finally the brightness bit and decimal point bits are assigned to another byte which then has the first digit’s nibble OR’d into it. Which leaves us with bytes a, b and c ready to send to the MC14489. Note that there isn’t any error-checking – however you could add a test to check that the number to be displayed was within the parameter, and if not either switch off the display (see example 51.1) or throw up all the decimal points or … whatever you want.

You can download the demonstration sketch for the function – Example 51.2, and view the results in the following video:

You can also display the letters A to F by sending the values 10 to 15 respectivel to each digit’s nibble. However that would be part of a larger application, which you can (hopefully) by now work out for yourself. Furthermore there’s some other characters that can be displayed – however trying to display the alphabet using 7-segment displays is somewhat passé. Instead, get some 16-segment LED modules or an LCD.

Finally, you can cascade more than one MC14489 to control more digits. Just run a connection from the data out pin on the first MC14889 to the data pin of the second one, and all the clock and enable lines together. Then send out more data – see page 11 of the data sheet. If you’re going to do that in volume other ICs may be a cheaper option and thus lead you back to the MAX7219.

Conclusion

For a chance find the MC14489 is a fun an inexpensive way to drive those LED digit displays. We haven’t covered every single possible option or feature of the part – however you will now have the core knowledge to go further with the MC14489 if you need to move further with it. And if you enjoy my tutorials, or want to introduce someone else to the interesting world of Arduino – check out my new book “Arduino Workshop” from No Starch Press.

LEDborder

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, COM-11405, freescale, LED, lesson, mc14489, motorola, tronixstuff, tutorial, vintage6 Comments

mbed and the Freescale FRDM-KL25Z development board

In this article we examine the mbed rapid prototyping platform with the Freescale FRDM-KL25Z ARM® Cortex™-M0+ development board.

Introduction

A while ago we looked at the mbed rapid prototyping environment for microcontrollers with the cloud-based IDE and the NXP LPC1768 development board, and to be honest we left it at that as I wasn’t a fan of cloud-based IDEs. Nevertheless, over the last two or so years the mbed platform has grown and developed well – however without too much news on the hardware side of things. Which was a pity as the matching development boards usually retailed for around $50 … and most likely half the reason why mbed didn’t become as popular as other rapid development platforms.

And now we have another powerful yet inexpensive board to use with mbed  – the Freescale FRDM-KL25Z

It’s a move in the right direction for both mbed and Freescale. It allows educators and interested persons access to a very user-friendly IDE and dirt-cheap development boards.

What is mbed anyway?

mbed is a completely online development environment. That is, in a manner very similar to cloud computing services such as Google Docs or Zoho Office. However there are some pros and cons of this method. The pros include not having to install any software on the PC – as long as you have a web browser and a USB port you should be fine; any new libraries or IDE updates are handled on the server leaving you to not worry about staying up to date; and the online environment can monitor and update your MCU firmware if necessary. However the cons are that you cannot work with your code off-line, and there may be some possible privacy issues. Here’s an example of the environment:

mbedcompiler

As you can see the IDE is quite straight-forward. All your projects can be found on the left column, the editor in the main window and compiler and other messages in the bottom window. There’s also an online support forum, an official mbed library and user-submitted library database, help files and so on – so there’s plenty of support. Code is written in C/C++ style and doesn’t present any major hurdles. When it comes time to run the code, the online compiler creates a downloadable binary file which is copied over to the hardware via USB.

And what’s a Freedom board?

It’s a very inexpensive development board based on the Freescale ARM® Cortex™-M0+ MKL25Z128VLK4 microcontroller.

Features include  (from the product website):

  • MKL25Z128VLK4 MCU – 48 MHz, 128 KB flash, 16 KB SRAM, USB OTG (FS), 80LQFP
  • Capacitive touch “slider,” MMA8451Q accelerometer, tri-color LED
  • Easy access to MCU I/O
  • Sophisticated OpenSDA debug interface
  • Mass storage device flash programming interface (default) – no tool installation required to evaluate demo apps
  • P&E Multilink interface provides run-control debugging and compatibility with IDE tools
  • Open-source data logging application provides an example for customer, partner and enthusiast development on the OpenSDA circuit

And here it is:

topside

In a lot of literature about the board it’s mentioned as being “Arduino compatible”. This is due to the layout of the GPIO pins – so if you have a 3.3 V-compatible Arduino shield you may be able to use it – but note that the I/O pins can only sink or source 3 mA (from what I can tell) – so be careful with the GPIO . However on a positive side the board has the accelerometer and an RGB LED which are handy for various uses.

Getting started

Now we”ll run through the process of getting a Freedom board working with mbed and creating a first program. You’ll need a computer (any OS) with USB, an Internet connection and a web browser, a USB cable (mini-A to A) and a Freedom board. The procedure is simple:

  1. Order your board from tronixlabs.com
  2. Download and install the USB drivers for Windows or Linux from here.
  3. Visit mbed.org and create a user account. Check your email for the confirmation link and follow the instructions within.
  4. Plug in your Freedom board – using the USB socket labelled “OpenSDA”. It will appear as a disk called “bootloader”
  5. Download this file and copy it onto the “bootloader” drive
  6. Unplug the Freedom board, wait a moment – then plug it back in. It should now appear as a disk called “MBED”, for example :

mbeddrive

There will be a file called ‘mbed’ on the mbed drive – double-click this to open it in a web browser. This process activates the board on your mbed account – as shown below:

registered

Now you’re ready to write your code and upload it to the Freedom board. Click “Compiler” at the top-right to enter the IDE.

Creating and uploading code

Now to create a simple program to check all is well. When you entered the IDE in the previous step, it should have presented you with the “Guide to mbed Online Compiler”. Have a read, then click “New” at the top left. Give your program a name and click OK. You will then be presented with a basic “hello world” program that blinks the blue LED in the RGB module. Adjust the delays to your liking then click “Compile” in the toolbar.

If all is well, your web browser will present you with a .bin file that has been downloaded to the default download directory. (If not, see the error messages in the area below the editor pane). Now copy this .bin file to the mbed drive, then press the reset button (between the USB sockets) on the Freedom board. Your blue LED should now be blinking.

Moving forward

You can find some code examples that demonstrate the use of the accelerometer, RGB LED and touch sensor here. Here’s a quick video of the touch sensor in action:

So which pin is what on the Freedom board with respect to the mbed IDE? Review the following map:

frdm-kl25z-pinout-final1

All the pins in blue – such as PTxx can be referred to in your code. For example, to pulse PTA13 on and off every second, use:

The pin reference is inserted in the DigitalOut assignment and thus “pulsepin” refers to PTA13. If you don’t have the map handy, just turn the board over for a quick-reference:

theback

Just add “PT” to the pin number. Note that the LEDs are connected to existing GPIO pins: green – PTB19, red – PTB18 and blue – PTB.

Where to from here? 

It’s up to you. Review the Freedom board manual (from here) and the documentation on the mbed website, create new things and possibly share them with others via the mbed environment. For more technical details review the MCU data sheet. And to order your own Freedom board, visit tronixlabs.com

Conclusion

The Freedom board offers a very low cost way to get into microcontrollers and programming. You don’t have to worry about IDE or firmware revisions, installing software on locked-down computers, or losing files. You could teach a classroom full of children embedded programming for around $20 a head (a board and some basic components). Hopefully this short tutorial was of interest. We haven’t explored every minute detail – but you now have the basic understanding to move forward with your own explorations.

visit tronixlabs.com

Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our forum – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in 1 hz, arm cortex, education, FRDM-KL25Z, freedom, freescale, lesson, M0+, mbed, MKL25Z128VLK4, MMA8451Q, opensda, part review, tronixlabs, tronixstuff, tutorial0 Comments


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