Serial Backpack for Avago HDLx-2416 Using Teensy

I purchased an Avago HDLS-2416 display from eBay a while back for my refrigerator monitor project (Fridge Squid FTW!).  This is a really nice compact 4-character 5×7 alphanumeric display, extremely bright and readable.

Unfortunately it was the wrong part; the 2416 is a parallel display, requiring 16 pins for normal operation.  What I *should* have ordered was a HCMx-29xx display, which is a serial device that already has Arduino support (check out the library on the PJRC site).

Last week while researching batch PCB creation on the dorkboxpdx site I stumbled across an interesting post by Ward Cunningham (yes, THAT Ward Cunningham).  In this blog post Ward describes how the 2416 is a near-perfect fit for the Teensy USB development board, a tiny AVR-based board from PJRC.  While Ward’s post focuses on using Txtzyme via the USB port to drive the display, it got me thinking about how to turn this display into a simple serial device that wouldn’t use up all of the ports on my Arduino.

I already had a couple of Teensy boards in my collection from my initial Arduino purchasing frenzy; I picked them up before I discovered the Arduino FIO, which is a much better fit for my wireless sensor project.  Sure enough, the 2416 display fits the Teensy like a glove, almost like they were made for each other.  I initially thought that I’d mount the display using low-profile female headers; soldered the headers on the board, plugged in the display, and…nothing.  Turns out that the pins on the Avago display are far too fine to make reliable contact with the female header that I had installed.  Oops.

I’ve gotten pretty good at soldering over the last couple of months, but desoldering? Not so much.  Removing the female headers took some doing, but eventually I got them removed and soldered the display directly to the Teensy.  Plugged everything in, uploaded Txtzyme to my Teensy and ran Ward’s yow! Perl script.  Very close – alpha characters worked fine, but no numerics or punctuation.  A bit of debugging and I found the problem.  In my haste to remove the female headers I had accidentally pulled the solder pad from one of the Teensy’s pins; a quick jumper to another digital pin, quick change to the perl script, and everything was right with the world again.

I spent some time banging out a simple bit of code to run on the Teensy, and will post the library up on my GitHub account once I’m happy with it.

This could be a nice solution if you wanted to include a HDLx-2416 or similar but were running out of digital outputs on your microcontroller.  This solution provides display integration with a single serial pin, rather than the five required for the serial HCMx-29xx serial display.

Edit: 7/24/2011: Found a source on EBay selling a bunch of these for a very reasonable price ($12.50); check out the auction here.


Don’t Be Afraid of Surface Mount Components!

While taking stock of the components I had on hand last weekend I found a small box of sample components that I had ordered from Maxim a while back; Two each of several components: DS2717 RTC, DS2438 Smart Battery Monitor,  DS2762 Hi-precision Li+ Battery Monitor with Alerts, and an DS2408 8-channel addressable switch.  These parts all have a couple things in common – first, they are all 1-Wire devices, but more to the point they are all surface mount components.  The 2717 is a TSOC-6, the 2438 is a SOIC-8, the 2762 is a TSSOP-16, and the 2408 is a SOIC-16.  And they are *tiny*.  Seriously.  My renewed interest in electronics and the Arduino spurred me on to research whether hand soldering was even possible with these parts, and I was pleased to discover that not only is it possible, it’s really quite easy as long as you use decent tools and follow a few simple guidelines.

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Whozz Calling 2

Finally, a Working Caller ID Solution: Whozz Calling 2

I’m still paying for a POTS telephone (land) line.  Whether it’s just basic paranoia or a product of growing up in the 70s, I just can’t bring myself to get rid of my land line.  For some reason, this cold war era technology gives me a certain degree of comfort.  Not that it’s entirely without merit; during the last appreciable crisis in the pacific northwest (the 2001 Nisqually earthquake, a magnitude 6.8 roller), cell phones were virtually useless; all circuits were busy.

One of my (admittedly numerous) goals in developing my own HA solution is to track all inbound and outbound calls on my land line.  This would allow me to actually measure usage to see if I’m actually getting my money’s worth, and opens the door to lots of potential features – automatically hanging up on known pesky callers, flashing caller ID on computers in the house, call frequency analysis, etc.   Continue reading


Hacking Eaton HomeHeartbeat Part 5: Ack! No Time!

Between one daughter’s wedding and another daughter’s surgery I haven’t had any time to play with this stuff this week.  I did, however, clean out my friendly Ebay vendor’s supply of $5 sensors for my collection, adding a few more motion detectors, a couple door/window sensors, and some other miscellaneous stuff.  Plenty of devices to tear apart and experiment with.  More information to come…