chembal.com

It’s been awhile since I’ve posted much here, so I thought I’d start it out by detailing my latest and greatest electronics project, the modernization of a practice drag racing christmas tree controller. Check out all the details on it’s electronics sub-page on the page navigation list, or click here. Enjoy!

Check out the progress I’ve made on my mailbox monitor! I’ve designed and fabricated the boards for both the server side and the mailbox side. On the software end, I’ve written the firmware for the microcontroller in the mailbox, and I’ve written at least a rudimentary server daemon to monitor mailbox state changes that have been relayed, and log them to a MySQL database. Next, I need to mount these two hardware pieces, and then get going on the UI side. My hope is still to make use of another ZigBee module hooked up to my small OLED display for real-time notifications, and maybe eventually some house control. Stay tuned!

If you’ve ever checked out my weather links on this site, you might have been curious how I’ve been posting them (or maybe just why).  I’ve been curious about the differences in temperature between different places in my house (especially in the attic where it gets crazy hot), and so I decided to hook up a bunch of digital temperature sensors.  I’ve already got a linux box humming along 24×7, so I figured it might as well take care of this task in addition to its normal file serving duties. Also, I had played with Maxim’s 1-Wire sensors previously, and so decided to use that as a cheap way to get the temperatures.

So, here’s my formula:

• DS18S20 1-Wire Digital Thermometers that I grabbed from here
• An HA7S 1-Wire Host Adapter
• A bunch of CAT5 running through the house
• A simple MAX232 interface to an unused serial port on my motherboard
• A simple java program I wrote to poll the 1-Wire bus and log the results to a MySQL database
• A couple PHP scripts to grab that data and serve it up either as text or as an XML/SWF Chart or Gauge

I decided on the HA7S as my host adapter mainly because it seemed to offer better range than the simpler direct interfaces Maxim offers as single chip solutions.  Using a simple interface would have actually saved a little coding, since Maxim has a nice Java library available for interfacing with 1-wire, but the HA7S was reasonably priced, and looked easy to interface, so I went for it.  It turned out to work as advertised, and was small enough that after I added a simple MAX232 based level converter it was still small enough to mount inside my server case.  This turned out to be a very elegant solution.  My motherboard (an Asus P5BV-C/4L) has a spare serial port onboard exposed via a standard 10-pin DIL header.  My case (an Antek 4U22ATX450-2) has a spare knock-out for a DB-9 connector.  So, I mounted my circuit inside the case, grabbed 5V from a spare disc-drive power connector, and hooked up the MAX232 to the motherboard header and the 1-wire output to a DB-9 connector in the spare knock-out on the case.  I used a female DB-9 connector so I wouldn’t accidentally mistake it for a standard serial port.  The end result was a very pleasing, clean, standard look from the outside, all for around $30-$40 bucks including sensors.  (Disclaimer: I had everything but the sensors and the HA7S on hand in my junk box.)

YMMV, but 1-Wire is a very forgiving electrical protocol.  In my case, I hooked up one sensor to a spare pair in a CAT6 run already going from my server rack (basement) to my bonus room (above garage).  Another sensor is on a separate run from the rack to the attic.  Another separate run goes to a box outside.  (Currently over-stating temps in the morning due to solar warming of the box.  I’ll redo this soon, I hope, in a more shaded area.)  The fourth sensor is mounted on my adapter board inside the server case.  This star topology is not really recommended by Maxim, but it seems to work okay for my limited installation.  My next step will be to hook up my outdoor sensor under an eve, running the cable to my attic sensor.  This more linear bus topology should be more reliable long-term.

I’ve been thinking about how I’m going to actually check the results from my Mailbox Monitor project, and I think I’ve got it figured out.  I’ve got a really cool OLED display that’s been burning a hole in my workbench, and I think that, coupled with an extra XBee module and a Freescale S08QE32 microcontroller are just the ticket.  All three items are 3V devices with low-power sleep modes which will conserve battery consumption.  When a packet of data comes over the XBee module, I will notify the microcontroller, which will then blink a couple obnoxiously bright LEDs for a minute or two to let me know something new came in.  I push a button, and the OLED turns on and shows me the latest info.  This could also be tied in with other sensors around the house, as XBee used a mesh communications protocol.  Should be neat!