|HD44780 Compatible display|
There are a number of advantages of an I2C implementation:
- Only two I/O pins are required.
- More i/o can be added on the same two wires.
- The lines can be longer than a parallel implementation and readily screened.
- The Atmel part has a native I2C port
- Lots of support in Arduino libraries
- Could be bit banged if necessary
The implementation was based on the LiquidCrystal_I2C for the Arduino using a Phillips (NXP) I2C chip PCF8574P as described in the libraries associated documentation. Using this device a serial communication can be achieved to a parallel I/O port. This essentially allows for a serial to parallel conversion and thus control of a HD44780 compatible LCD display device as used in the Panelolu design. The chip also has bi-directional i/o ports. Thus supporting input as well as output. So the plan was to use two devices one for the display and one for the switches etc.
The good, the bad and the ugly...
The great thing about open sources is that you get to benefit from lots of people working on projects thus 'standing on the shoulders of giant's'. Simultaneously of course you can find yourself working in parallel on a blind alley. In this case I selected the chip as the library seemed well supported and the chip is low cost, with alternates out there that would not lock a solution into one device.
|LiquidCrystal_I2C implementation from the notes|
So I have decided to junk the Philips part and switch to the Microchip part as one part will support both the LCD and the keboard.
Whilst doing this, I also developed a CAD model to allow me to implement a neat box for my display and keyboard. If you would like a copy of the HD44780 STEP model for the 20 x 4 model, you can download it from here. You can get the software configured for Huxley #710 here. I have no intention of taking this software forward in this form at the moment. I have ordered the Microchip part so that I am hardware compatible with the upcoming Panelolu implementation.
Either way, I will have Huxley #710 running with the Microchip part by the end of January at the latest. Until then, the LCD panel with the Philips part is fantastic. The temperature updates are rapid and the status updates on the display are very handy.
|RS 720-0226 Fordata FDCC2004B-FLYYBW-51SE|
I may yet implement the Nokia 5110 display with Huxley #710, a graphic of the part being printed would be cool on a progress style screen. At the moment though we are just having too much fun printing and working with our new glass table!
|Sparkfun Nokia 5110 LCD Display CAD mode|