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Tag Archives: 3410
LCD testing for Decimus
Having installed the LCD, it was time to get the code working for it. First I realised that it may not have been so clever to put the LCD on the same SPI port as the encoders. This will mean that I have to take care that the encoders are not being read when the LCD is active. Since the encoders are sampled every interrupt, it means turning them off while writing to the screen. That, in turn, means not writing to the screen while moving, or holding position. I may end up having to patch the board to put the LCD on the other SPI port. In fact, I wish I had done that in the first place as it would just share lines with the UART and I could easily switch between the UART and the SPI for writing debugging messages. Ah well, live and learn.Turns out I wired up the LCD module incorrectly and destroyed it. Fortunately I had several spares so I built up another. These things are cheaper than text displays so it is no great loss. Attaching wires to the LCD display is easier than you might think. As supplied, the Nokia 3410 LCD display comes as part of a replacement panel that looks like this:
Prise off the aluminium surround and the actual display element will come free. It is attached with a small amount of adhesive or double-sided tape. Sprung contacts serve to make the connection between the display and the phone main board. These too are attached with adhesive and can be removed to reveal a row of small pads to which you can solder wires. [See warning in comment below before removing this connector]. I used polyurethane coated copper wire from a Verowire pen (about 0.15mm diameter). The ends of the wires are stripped by simply heating with the soldering iron set to about 400 degrees Fahrenheit:
These wires are then taken to pin headers on a matrix board so that the entire assembly can be plugged into the mouse when needed. once the connections have been tested, the LCD is held onto the carrier with some double-sided foam adhesive pads.
It does not weigh much and could probably be left in place when running. The mouse looks a lot better with it off though. For now, a simple ‘hello’ is enough to show that it works.
LCD screen for Decimus
Probably the last part to be added to Decimus will be the Nokia 3410 LCD screen. Nearly all of my mice have these either permanently fitted or attached by a simple socket so they can be removed. With a resolution of 96×64 pixels, this screen is an ideal debugging aid. The display is relatively simple to drive if you have an SPI port available. The more commonly available 3310 screen has a lower resolution and cannot easily display a picture of the entire maze. With the 3410 model, it is possible to either show the maze or to have 8 lines of 16 characters of data displayed.
Because Decimus is the most compact micromouse I have yet built, the display sits on a couple of small riser boards, made from veroboard, to allow it to clear the motors and batteries. Not only is the graphical LCD smaller than the more common 16×2 text display, it is cheaper and lighter. With a bit of care, the display can replace many, if not all, the practical functions of a real-time debugger.
Adding a timer and the graphical LCD
This is a fairly big jump. With the LEDs and buttons tested, it is time to add the main graphical display, made from a Nokia cellphone display. Also, there is the main system timer event.
The simple user IO is working, and it is time to add a system timer. This will generate an interrupt every millisecond. In the final mouse a lot of work will be done in here – processing buttons, driving the LEDs, reading sensors and calculating drive signals for the motors.While that may seem a lot in a millisecond, the dsPIC used in primus can execute about 16,000 instructions in that tme and we should only need a small proportion of that time.Another function of the timer will be to maintain an internal clock so that the main program can time events and produce more reliable delays without holding up everything else. We shall continue to use the already present delay functions when it is acceptable for delays to be a bit rough, very short (less than 100us) or when the blocking behaviour is not going to cause any problems. The interrupts from the system clock will make the software delay functions run slow – possibly very slow so they can no longer be relied upon for anything but the simplest, non-demanding tasks.The system timer interrupts come from a 16 bit timer which will run continuously as long as the mouse is turned on. Since actually configuring the timer is pretty simple, this example will make use of the timer to debounce button presses, flash the LEDs and produce tones from the speaker. Trivial really.As with the other examples, the timer has its own source code module and header. Unlike the others, it is a relatively high-level module and must be able to call functions defined for the LEDs and buttons, and later for the sensors and motors.While we are at it, the nokia LCD is working. The test code should display a start up message followed by the Primus splash screen when you press a button. After that, pressing buttons will change the picture. This is just to show off the fact that it works. The LCD will become an essential tool in debugging and setting up so don’t leave it out.While the demo code displays pictures, these take up quite a bit of flash memory – about 760 bytes each – and they are not really needed. I like to put a splash screen up after a restart – just because I can. The images are a bit of a fiddle to create. I make a 2 colour image in PaintShop and save it as a RAW image file. A utility I have will read that file and convert it into the C definition you see in the source code.Remember that the display I have has 96×65 pixels. Try to get the right one if you are to avoid re-writing some of the driver code. Actually, the text stuff will work fine but you get shorter lines and fewer of them so take care.The complete project for MPLAB contains all the source code, the object files and som HTML documentation generated by Doxygen.Primus3.zip Continue reading
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