Monday, March 11, 2013

Arduino and KTM-S1201 LCD modules

Learn how to use very inexpensive KTM-S1201 LCD modules in this edition of our Arduino tutorials. This is chapter forty-nine 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.

Introduction

After looking for some displays to use with another (!) clock, I came across some 12-digit numeric LCD displays. They aren’t anything flash, and don’t have a back light –  however they were one dollar each. How could you say no to that? So I ordered a dozen to try out. The purpose of this tutorial is to show you how they are used with an Arduino in the simplest manner possible.

Moving forward – the modules look like OEM modules for desktop office phones from the 1990s:

With a quick search on the Internet you will find a few sellers offering them at that price. The modules (data sheet) use the NEC PD7225 controller IC (data sheet):

They aren’t difficult to use, so I’ll run through set up and operation with a few examples.

Hardware setup

First you’ll need to solder some sort of connection to the module – such as 2×5 header pins. This makes it easy to wire it up to a breadboard or a ribbon cable:

The rest of the circuitry is straight-forward. There are ten pins in two rows of five, and with the display horizontal and the pins on the right, they are numbered as such:

Now make the following connections:

  • LCD pin 1 to 5V
  • LCD pin 2 to GND
  • LCD pin 3 to Arduino D4
  • LCD pin 4 to Arduino D5
  • LCD pin 5 to Arduino D6
  • LCD pin 6 to Arduino D7
  • LCD pin 7 – not connected
  • LCD pin 8 – Arduino D8
  • LCD pin 9 to the centre pin of a 10k trimpot – whose other legs connect to 5V and GND. This is used to adjust the contrast of the LCD.

The Arduino digital pins that are used can be changed – they are defined in the header file (see further on). If you were curious as to how low-current these modules are:

That’s 0.689 mA- not bad at all. Great for battery-powered operations. Now that you’ve got the module wired up, let’s get going with some demonstration sketches.

Software setup

The sketches used in this tutorial are based on work by Jeff Albertson and Robert Mech, so kudos to them – however we’ve simplified them a little to make use easier. We’ll just cover the functions required to display data on the LCD. However feel free to review the sketches and files along with the controller chip datasheet as you’ll get an idea of how the controller is driven by the Arduino.

When using the LCD module you’ll need a header file in the same folder as your sketch. You can download the header file from here. Then every time you open a sketch that uses the header file, it should appear in a tab next to the main sketch, for example (click to enlarge):

There’s also a group of functions and lines required in your sketch. We’ll run through those now – so download the first example sketch, add the header file and upload it. Your results should be the same as the video below:

 

So how did that work? Take a look at the sketch you uploaded.  You need all the functions between the two lines of “////////////////////////” and also the five lines in void setup(). Then you can display a string of text or numbers using

ktmWriteString();

which was used in void loop(). You can use the digits 0~9, the alphabet (well, what you can do with 7-segments), the degrees symbol (use an asterix – “*”) and a dash (use  - “-”). So if your sketch can put together the data to display in a string, then that’s taken care of.

If you want to clear the screen, use:

 ktmCommand(_ClearDsp);

Next – to individually place digits on the screen, use the function:

ktmPrnNumb(n,p,d,l);

Where n is the number to be displayed (zero or a positive integer), p is the position on the LCD for the number’s  (the positions from left to right are 11 to 0…), d is the number of digits to the right of the decimal point (leave as zero if you don’t want a decimal point), and l is the number of digits being displayed for n. When you display digits using this function you can use more than one function to compose the number to be displayed – as this function doesn’t clear the screen.

To help get your head around it, the following example sketch (download) has a variety of examples in void loop(). You can watch this example in the following video:

 

Conclusion

So there you have it – an incredibly inexpensive and possibly useful LCD module. Thank you to Jeff Albertson and Robert Mech for their help and original code.

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.

Wednesday, March 6, 2013

posterous is closing at the end of April

Hello everyone

If you're following this blog, please switch to the main site at

http://tronixstuff.wordpress.com 

- as posterous is shutting down at the end of April.

 

Thank you

John Boxall.

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.

Also – a few months ago – we received the new Freescale Freedom FRDM-KL25Z development board from element14. I started to write about using the board but frankly it did my head in, as at the time the IDE was almost a one gigabyte download and the learning curve too steep for the time I had available. Which was a pity as the board is inexpensive and quite powerful. So the board went into the “miscellaneous dev kit” box graveyard. Until now. Why?

You can now use the Freedom board with mbed. 

It isn’t perfect – yet – but 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 (click to enlarge):

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. How inexpensive? In Australia it’s $9 plus GST and delivery.

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:

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. Note that the board ships without any stacking header sockets, but element14 have a starter pack with those and a USB cable for $16.38++.

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. Australians can also get a board from Little Bird Electronics. The procedure is simple:

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

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 (click to enlarge):

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:

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:

#include "mbed.h"
DigitalOut pulsepin(PTA13);
int main() { while(1) { pulsepin = 1; wait(1); pulsepin = 0; wait(1); } }

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 (click to enlarge):

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.

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.

The Freescale Freedom FRDM-KL25Z development board used in this article was a promotional consideration supplied by element14.

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 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.