Friday, May 6, 2011

Arduino notebook: 16x2 LCD display (Part 2)

How to change the default behavior


My last article in this series talked about why I chose Sparkfun's Serial Enabled LCD display kit and how to build it. One of the reasons it caught my eye was because it uses an Arduino as the controller for the display. I figured it was pretty busy doing nothing most of the time and thought it could be used for other purposes in addition to driving the display. Upon further investigation, it turns out I was right.

Nicole, a friend of mine, recently e-mailed me about a photography project she was interested in doing but didn't want to spend the money for a professional rig to do some of the things involved. She asked if I had any ideas. I'd already given some thought to the problem, the investigation of which led me to the Arduino platform in the first place. This project was one I had stewing on the back burner for quite a while and it was now time to turn up the heat on it.

One of the requirements was to be stand-alone. It had to allow for some user configuration at the time of use in battery mode, without any other devices attached. This ruled out the obvious easy solution of setting the parameters via USB through a computer. Also, it involved controlling a stepper motor. I immediately thought of the LCD kit. I knew I would at least use it for the display, and hopefully some toggle switches. I had a distant hope I could also use it for the motor control. Since this was going to be a pretty permanent build, I immediately ordered another LCD to use specifically for this project.

After getting a new display on the way, I pulled out my first kit to take a look at it. Sure enough, it had a handful of empty holes on the PCB labeled with both digital and analog pin assignments. Cool. It had enough extra pins to accomodate everything I needed to do. So, I started work on the rest of the project while I waited for the LCD to arrive. (The other details of this project I'll write about in future articles here and on my photography blog Hooked On Light.)

First thing after getting the new kit, I assembled it. It went much faster this time with no of the frustrations I experienced on the first one. It actually worked the first time I applied power.

One of the biggest things I did differently was to use ribbon cable between the display and controller boards. In some ways this made things easier and in other ways it was harder. I think on the next project I'll probably put the header pins that come with the kit in one board and get a socket to solder onto the other board. That will give me a cleaner build like the first one, but with the ability to separate the boards for easier access like I have with the ribbon cable on the second one.

The web site to order the kit indicates the firmware can be reprogrammed with an FTDI Basic Breakout board. I had ordered one with the first kit, but hadn't had a chance to use it prior to this project. Knowing I needed to use this, I also purchased some 90 degree header pins from my local electronics parts supplier and soldered them into the holes on one end of the board designed for the purpose. This allowed the FTDI board to plug onto the controller board, providing a plug for a USB cable to be plugged in.

Now I started looking for instructions on how to actually reprogram the thing. The order page indicated you needed to change a setting in the Arduino IDE and referenced the github page for further instructions. Well, the github page had no other instructions on programming the thing. All it talked about was how to use the board through the serial interface. The software for the firmware was also hosted there. Besides the one sentence on the order page, I couldn't find any other instructions either on those two sites or anywhere else via web searches on how to reprogram this kit.

Reprograming the kit

I figured, no guts, no glory and decided to experiment some. I downloaded the source code from github, loaded it in the Arduino IDE and made a simple change to the splash screen text. Since the splash screen is the first thing you see, I thought this would be an easy way to verify if my changes worked or not. In the IDE, as instructed on the order page, I changed the target machine to Arduino Duemilanove or Nano w/ ATmega328 and hit the upload button.

It compiled.

It uploaded.

And when it reset after the upload, there was my new splash screen text.

Amazing. That was all there was to reprogram the kit's default software. The reason I couldn't find any other instructions was, there weren't any other instructions needed.


After this success, it was simply a matter of changing things to do what I needed it to do for this project. Essentially, I ripped out everything the existing software does and replaced it with what I needed. There are a few lines to initialize the LCD and one function to write characters to the screen that are the same, but everything else is completely new.

Now that I've found how easy this is to repurpose, I think I'll probably use it for other projects in the future too. It's an easy way to get an entire Arduino system up and running in a clean package with a simple user interface and minimal external support circuitry needed.

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