Saturday, July 11, 2009

Quickcoms 2 : Pocket Term

I started this project in 2006 while I was living in Japan with an idea to enter it in the 2006 AVR competition. Some things went astray with the hardware design so I dumped it in order to do five other more viable entries. The concept for the project was to take my Quickcoms Renasas design from 2005 and develop it further from the prototype. I mostly wanted to add keyboard support so it could act as stand alone terminal in addition to just decoding serial data. I also wanted it to be the size of a deck of cards and support a LiION battery. I wanted to enlarge the LCD to get closer to 80x40 chars on screen. Include support for a couple of LCDs on the PCBs to allow for a black and white low power version.

What went wrong ( other than trying to put the moon on a stick) ?

  • I made an assumption about the keyboard from the AVR application note that I would not have to send any data to the keyboard. Most AT keyboards will work without you sending any data back towards them so long as you don't wish to change the status LEDs. I bought a neat little keyboard to go with project from one of the many electronics dens around Akihabara. I wanted something small and light to throw in a toolkit without taking up all the room. Unfortunately this keyboard used an obscure chipset which follows an old protocol which purposely sends a malformed packet and waits for you to send an error response. With no scope or Logic analyser at the time this was a pretty big nail in this projects coffin. Although it only required a couple of small changes to the PCB and some voltage dropping resistors to configure the ATMega16 to transmit I managed to procrastinate this for two years.
  • I managed to blow up the back-lighting on the LCD display. Took me a while to get around to ordering a replacement.
  • I didn't provide a decent positive and negative supply rail for the op amps. I tried to rely on the comms transceiver chip to provide this. Unfortunately it was supplying 1 quad opamp and several multiplexes it and seemed to fall over completely. In my prototype I simply used a MAX232ACP with onboard capacitors to provide my circuits with the rails. I had assumed the new transceiver chip would be able to do the same.

Where is it at now?

Well after sorting out the keyboard issue and replacing the LCD I have a small screen that will echo characters from the PS2 keyboard and from PC via a USB serial port. What needs to happen next is sorting out a positive and negative voltage rail to support the multiplexers and opamps. Once that is done I can start porting the code from the original system over to the AVR.
After that is complete I can add the extra features such as logging to the screen, save and replay sessions, and saved macros.

And then What?

After that there is the case (already partially designed) and publishing documentation of the project for the website.