Electronic badges

[Colin McGregor]

As noted in my posting about the Ontario LinuxFest I
am opening up the electronic name badge can of worms
again. So, with that in mind let note the strengths
and weaknesses of the last (well only) electronic name
badge that I made (and keep in mind that I did this
about 10 years ago, some of the choices I made then I
would NOT do again...).

The brain of the badge was a PIC based BASIC stamp, a
device the size of a 9V battery. A revised version of
which can be seen here:

  www.parallax.com/detail.asp?product_id=27100

So, I took a project box mounted a 16 character x 1
line LCD module in the lid. On the back of the box I
attached 2 adhesive name badge pins. Inside the box I
put in the BASIC stamp and a 9V to power everything. 8
wires (4 for data, 2 for control, power and ground)
between the BASIC stamp and the LCD module and I was
done. Throw in a short program written in BASIC and
done. Fairly quick, fairly easy. not that cheap.

So what was wrong with the above? A few things. The
LCD module I used did offer a back light, if I could
supply the module with 100 V AC at 400 Hz. There are
circuits available that will take 9V and convert to
something, but more time, trouble, cost and loss of
battery life than I considered acceptable. So, while
the LCD module was easy to read in bright to moderate
light, in dim light it was unreadable...

The BASIC stamp has 256 bytes of EEPROM memory, which
needs to be shared between program and data storage. I
could pare the program down to the point where I had
some 170 characters of text messages to be scrolled
through on the badge, still, painfully modest...

A neat trick of the LCD modules I was using (and it is
a trick that is I gather common to many LCD display
modules) is that I could write data out to the module
4 bits at a time, which was crucial. Because the BASIC
stamp only has 8 IO lines I had to feed the data out 4
bits at a time, which is another way to say some of
the programming got a little (but not very) weird.

Programming the stamp required (and requires) access
to a box running Windows, which wasn't an issue for me
10 years ago, but now that I no longer have a full
time Windows box, would be a bit of a problem...

The biggest pain for me was weight distribution.
Enough weight was far enough forward that the badge
always wanted to tip downwards, so the LCD would face
towards the ground. Now, this is arguably an issue of
biology, the fattest male GTALug members and all
female GTALug members would not face this as an issue
(depending on where they pinned the badge on their
clothes). But still, for me weight distribution in the
badge was an issue.

So, what was right about the design I did? A few
things, starting with the fact that the thing worked,
and was fairly easy to build. 

Battery life on a standard 9V battery was most of a
day.

Made for a great conversation piece.

The inspiration for the badge came from seeing three
guys at a science fiction convention that had (working
together) done three PIC microprocessor based 64 LED
badges (each guy wearing one of the badges). I wanted
something comparable. So, my badge was scrolling words
rather than a little light show, and mine was clearly
a lot chunkier than the almost elegant, small badges
those guys had.  Still, I had what I wanted, namely
something semi-comparable ...

So, what would I do if I were starting this project
again from scratch? The BASIC stamp was the most cost
effective option at the time, but no more. Some of the
AVR chips seem to be a more cost effective option
(more memory, less money and Linux based development
tools available). As the focus has been message,
rather than light show, I would still tend towards
looking at LCD display modules even though an LED
based option could be cheaper. I would want to keep
the cost down so that it would be easy/cheap to say
build a dozen badges... I would want a thin badge
(back to front), as I don't want a badge that wants to
face the floor, so I would look at how to mount stuff
around the badge, with the batteries either at the
bottom of the badge, or run a wire to a seperate
battery pack that could drop in a shirt pocket.


Colin McGregor

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