PRODUCT OVERVIEW
Carl Livinston's My_LCD Serial Backpack is an ATTiny2313 system which interfaces a 14-16 pin HD44780 text mode LCD screen to a simple, one-pin RS-232 input line at up to 115200 baud.
ORDERING
I initially communicated with Carl (microcarl) via AVRFreaks private message and later e-mail. Our exchanges have been very pleasant, productive, and interesting. We agreed upon a trade and Carl was very generous in supplying me with 3 prebuilt/tested serial backpacks and 2 bare serial backpack boards. (I already have a significant number of LCDs that I wish to connect to these backpacks).
BUILD QUALITY
Build quality is top-notch. Carl has generously detailed his home-brew techniques in multiple messages on avrfreaks. By far, these are the nicest home-made PCB's I've encounted. The prebuilt units worked flawlessly on first attempt. My understanding is that Carl may soon acquire additional equipment to produce even better boards, but his homebrew PCBs are already excellent.
HARDWARE MODIFICATIONS
Carl has published very detailed documentation on his board and firmware. With his text descriptions, schematic, and board layout, I modified two of the boards to accept TTL mark/sense levels rather than the default RS-232 inverted voltage levels. This was easily accomplished by removing R1, R2, and Q1 and then soldering a jumper wire from the second pin of HD1 to pad of the now-removed R2. Carl's PCB held up well to the desoldering and resoldering of connections.
The RX line modification works very well for connecting the Serial Backpack to Smiley's USB-BB which output TTL-logic levels for serial communication.
Since I had some firmware changes I wanted to make, I performed a second modification to allow use of debugWIRE. First, I used ISP programming to set the fuses of the ATTiny2313 to allow debugWIRE and to disable the RESET function on the RESET pin. Carl gives directions on how to use ISP in his documentation. Then, I removed C3 and soldered a jumper wire and a pin on to the side of the C3 pad going the RESET pin for using debugWIRE with a JTAGICEMkII programmer/debugger. The advantages of using debugWIRE over ISP for programming are integrated programming and debugging and being able to program/debug the serial backpack while the LCD is connected to the serial backpack. Thus, I was able to debug my below software modifications while the LCD was operating.
SOFTWARE MODIFICATIONS
Carl kindly provides source code for his firmware for personal, non-commerial use. I made extensive additions and changes to it to provide IAR and GCC support as well as interrupt-driven UART with circular buffer, PWM LED brightness setting, idle sleep mode, and watchdog timer. I've given copies of my code to Carl which he may include in future versions of his software.
Carl also provides a testing program for a ATMega8535 controller. I ported that over to Cygwin so that I can run the test suite from my Windows system. While I haven't tried it, that same set of modifications for Cygwin will also likely compile and work fine on Linux.
Addendum: An example of Carl's flexibility and generosity: during the discussion of licensing and redistributing the changes I made to his firmware, Carl very generously opened his license to redistribution of modified versions as well as full commercial usage. His license text is fairly similar to the quite permissive BSD license -- only simpler. Kudos to Carl for his generous donation of code.
SYNERGY WITH USB-BB
It is very nice using the My_LCD Serial Backpack with Smiley (Micros) USB-BB; not only because it provides a USB connection to a PC (rather than a legacy serial port), but also because the USB-BB provides power to the serial backpack as well. Thus, no external power supply is needed for the serial backpack.
OVERALL IMPRESSION
This product works great and I've already incorporated into two projects. At this point, I'd be reluctant not use his product when I need to incorporate a HD44780 LCD panel in a design. The ability to communicate with the panel with a single pin rather than 7-11 pins can be an essential win for many designs.
My communication with Carl has a true pleasure and Carl's work is first-rate. Many thanks to Carl for his useful contribution to the AVR community. I hope Carl continues his hardware and software design. Given my experience, I'd use any of his products without hesitation.
Edit: Fix spacing
