Review of Microcarl's My_LCD HD44780 Serial Backpack

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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

Last Edited: Sun. Dec 9, 2007 - 07:10 AM
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Kevin, Carl and Eivind,

I think that this posting highlights the value of another forum, 'Product Reviews', where similar AVR based products could be reviewed.

What do you think?

Cheers,

Ross McKenzie ValuSoft Melbourne Australia

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That makes sense, Ross. I know there's the Academy forum, but that's only for projects from the AVRFreak projects. I wasn't sure if Carl's project was listed there.

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kmr wrote:
That makes sense, Ross. I know there's the Academy forum, but that's only for projects from the AVRFreak projects. I wasn't sure if Carl's project was listed there.

Well, the My_LCD Serial Backpack is posted in the Academy section. Though, I'm not sure how hard it is to find by other AVRFreaks. When I posted the project, the web-site provided a link to it on the forums home page. So it's only a click away for me. I assume that this is the case for all projects posted, the author gets a direct link to the project.

The academy link to the My_LCD Serial Backpack is:

https://www.avrfreaks.net/index.p...

And Kevin, thanks for the great review!

It's very well done...

I'm currently negotiating with my employer to have 100 serial backpack PCBs made, as they order PCBs for customers on nearly a daily basis. If things work out, these will remain single sided but have solder-mask and component legends, as well. At that time, I'll be offering blank PCBs, kits and fully assembled and tested serial backpacks for sale. In addition, by the first of the year I'll be offering serial backpacks that will consist of pre-programmed Tiny2313s in the SOIP package.

And, hopefully, on, or around the first of the year, I'm hoping to have a basic web-store open to sell the growing accumulation of products that I've been developing.

There currently isn't anything there but you'll be able to find my web-store front at:

http://www.livingstonelectronics...

The actual time frame of the store front arrival depends on how much time the U.S. military allows my oldest son, Andrew, to spend on development.

Again, thanks for the great review Kevin

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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microcarl wrote:

I'm currently negotiating with my employer to have 100 serial backpack PCBs made, as they order PCBs for customers on nearly a daily basis. If things work out, these will remain single sided but have solder-mask and component legends, as well.

Since this would be a commercial (or at least commercial-ish) endeavor, if you do it under a business name, you could make use of 4pcb's $500 free offer for new customers. I would think that would make a pretty decent run of them.

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microcarl wrote:
I'm currently negotiating with my employer to have 100 serial backpack PCBs made, as they order PCBs for customers on nearly a daily basis. If things work out, these will remain single sided but have solder-mask and component legends, as well. At that time, I'll be offering blank PCBs, kits and fully assembled and tested serial backpacks for sale. In addition, by the first of the year I'll be offering serial backpacks that will consist of pre-programmed Tiny2313s in the SOIP package.

And, hopefully, on, or around the first of the year, I'm hoping to have a basic web-store open to sell the growing accumulation of products that I've been developing.

There currently isn't anything there but you'll be able to find my web-store front at:

http://www.livingstonelectronics...

You're quite welcome, reviewing your product was a pleasure. That's great news about a larger production run and also setting up your web store. That will be a significant service for the AVR community.

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Gluteal-Cleft wrote:
Since this would be a commercial (or at least commercial-ish) endeavor, if you do it under a business name, you could make use of 4pcb's $500 free offer for new customers. I would think that would make a pretty decent run of them.
I signed up for the $500 free offer, but I didn't quite find the details of what "$500 of free stuff" they were offering.

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Sorry that I forgot, but here's link to Carl's My_LCD Serial Backpack project: https://www.avrfreaks.net/index.p...

If you haven't read his PDF documentation, you might wish to -- it's very well done.

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microcarl wrote:
(...)
I'm currently negotiating with my employer to have 100 serial backpack PCBs made, as they order PCBs for customers on nearly a daily basis. If things work out, these will remain
(...)
And, hopefully, on, or around the first of the year, I'm hoping to have a basic web-store open to sell the growing accumulation of products that I've been developing.
(...)

Great step, Carl!
I wish you the best successes.

Embedded Dreams
One day, knowledge will replace money.

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I posted my modification's to Carl's excellent firmware that adds features such as LED PWM backlighting, interrupt-driven UART buffer, sleep mode, and watchdog timer.

Edit: The URL for the zip file of this modification of the firmware is https://www.avrfreaks.net/index.p...