GPSDO Display is in the works

As part of the GPSDO project I’ve been working on using a graphical display I picked up from Futurlec several years ago, a 128×64 Blue GLCD (CM12864-2) which uses the KS0108 chipset.

IMG_20150819_185714As I want to drive this from a Beaglebone Black I’ve opted to use a GLCD Backpack from Sparkfun to simplify the hookup and interfacing, sending serial commands should be far easier than sorting though GPIO… at least it _should_ have been.

The first issue is the backpack pinouts don’t match the pin layout on the LCD I have, so I’ll have to make up an adapter board.  Some breadboard does the job while developing so not a huge issue there.

IMG_20150819_185721The standard firmware comes with a number of simple operations for displaying text and some basic geometry operations, functional but nothing flash.

Unfortunately I found the standard firmware to be a little slow on the refresh rate and came with two standard fonts, big and bigger.

A little research found an updated set of firmware listed at the bottom of the page.

I modified this to include a small 3*5 font reminiscent of 80’s era computer games in place of the standard ‘large’ font, and quickly put together a nice summary page for the state of the GPSDO.



IMG_20150819_185703There are some minor dislikes for the font, for example the ‘H’ and ‘N’ characters are identical, but it works well enough that I may live with it.

The software was written in perl and may be shared later, its all very straight forward decoding of the GPS messages and sending serial data to the display so nothing complex in there.   I have included a ‘deltacache’ which detects data changes so only updates are posted to the LCD to conserve the limited serial bandwidth and avoid buffer overflows as I don’t have any flow control at this stage as the ‘TX’ pin isn’t connected to the BBB to avoid damaging the 3v IO pin.

All in all I’m happy with the results so far.   I still have a lot of work to do but this is a promising result.