Archive for June, 2011


DIY HVAC zoning


Last December (just in time for the “perfect storm” of energy credits…) we had a new heat-pump installed to replace the old gas furnace.  Additional work was done to run ducts to my office upstairs.  The plan was to make the upstairs actually workable during the summer, rather than having the window unit chill the office overnight, then lose the battle at 2 or 3pm and effectively end my productive work day.  So far the system has worked nicely, though the actual compressor has been a persistent noise problem (which Carrier is slowly working on).

The problem is, there really is no such thing as “balance” in a straight ducted system like this.  If the heat is on at any point, the duct to upstairs has to be completely closed off in order to not boil me alive, since there’s plenty of existing heat-producing equipment on my desk.  If it switches to cooling mode, I have to open the duct lest the ambient temperature ooze through the roof and equally boil me alive.  To help this later situation the installation included a duct-assist fan for the upstairs registers, which has to be turned on in many cases to get enough cold air (which is heavy and doesn’t want to go upstairs) where it needs to be.

Unfortunately, the assumption that there would be enough air return “falling” down the stairs hasn’t turned out to be true, which means I’m likely going to have to look into adding return registers and figuring out how to route a duct alongside the supply to the basement.  That’ll mean disassembly of the supply duct because it was positioned in the middle of the available space….

All of this is of course a preamble to the real topic (as per the, um, topic line) of this post, which is my plans to turn this into a zoned system.  The actual meat is after the break…. Read the rest of this entry ?


I have a friend at Fedex ;-)


So there I was yesterday, placing an order with Digikey for some spacers, LEDs, pins, etc.  It’s 4:50pm on Thursday, and the parts aren’t exactly time-critical, but I go with the company-standard Fedex Economy (2-day), expecting them on Monday or so.

Then a couple minutes ago (1:25pm Friday) through my headphones I hear somebody shouting outside, competing with the lawn equipment grinding away nearby.  Headphones come off, and it sounds like my name…. Huh?  Then I recognize the local Fedex driver’s voice and run downstairs, apparently I missed the doorbell (gotta find a solution for that).

He hands me a Digikey box, and I’m thinking “was there another order before this I forgot about???”.  He points to the “Monday” on the box and says he’s just “getting a jump on things”.  Out comes the leatherman, and out come the parts I ordered 22 hours and 25 minutes ago…..  These early deliveries are becoming a common event with this driver, and I’m definitely not complaining <g>

Making it even more amazing, one of the parts I ordered was a replacement for some parts Digikey mis-picked for the big assembly order.  I got a call from them around 5pm yesterday and he said he’d try to make sure the confusion with the parts was dealt with before the order shipped out.  I only got the shipment notification from them at 10:51 this morning.


Bootstrapping the new boards


So far so good with the new boards.  I started very carefully by feeding it 5V on the intermediate rail to see if the 3.3v supply comes up, which it did.  Next was hotwiring the microcontroller to my AVR-ISP mkII and confirming the chip is happy, then replacing that with one of my program/debug boards and connecting it to my isolated 8-channel programmer:

I’m taking the old codebase and rebuilding it module-by-module so I can clean things up as I go, and make the main loop more configurable for various experiments.  After getting the serial port (which is running over the same cable, to my programming board) up and running, I moved on to the FD77T (which is an CDCE949 + crystal).  Now I’m starting to build in all the other subsystems necessary to get the thing actually talking to other units…


Fully-assembled boards


I got a call yesterday that triggered a mad dash to try to get to Canby by 5pm to grab the freshly assembled PCBs.  Not sure they wouldn’t have answered after 5pm, but didn’t want to take the chance, eh? ;-)

The only error was actually caused by Digikey, where somehow they managed to stick a cut tape of some random SOT23-5 part inside a bag marked for SC70-6 parts…  I’ll have to figure that one out with them and mount those parts myself.  Luckily those are on the controller boards, of which there are only 3.

I have to assemble the 3rd board of each stack myself, because I ran them on the DorkbotPDX group order.  That’s because they’re simple by design, so I can run variations more frequently (and cheaper) as I work on fine-tuning that part of the product.  That and the debug board (which I have to solder a cable to) bracket the above boards, making the whole thing quite colorful ;-)

Part of my design is careful re-usability of parts.  The interface boards I’ve designed for upgradability are also snapped onto the controller, so if I come up with a better version I can replace the controller’s interface just as easily as all the others.

The next step of course is to bootstrap them, which is always a very nerve-wracking procedure…  It begs the question though: if the boards are red and purple, what color of smoke should come out if something goes wrong???