Automating heating vents with openHAB, esp8266 and LEGO - Part 3; Firmware intro

Continuing to work up the stack from my LEGO physical vent manipulator(V1), (V2), I decided to do something new for the embedded control software part of this solution and employ an Expressif ESP8266-based chipset and an accompanying L293D H-bridge daughterboard, primarily because they are just ridiculously cheap.

It took a little bit of finessing to find out exactly what to search eBay for (try ESP-12E + L293D) but listings like this, for AUD$12.55 including postage are simply incredible value. That's an 80MHz processor, motor driver board, USB cable and motor cable, all for less than I probably paid for the serial cable I would have used for my primitive robotics exercises back in university. Absolutely extraordinary.

As this setup uses the "NodeMCU" framework, it can be developed in the Arduino Studio IDE that I've used previously for Arduino experiments, in Arduino's C++-esque language that is simultaneously familiar, but also not ...

But I digress. The real trick with this board package is deducing from the non-existent documentation, exactly what you have and how it's meant to be used. For this particular combination, it's a "Node MCU 1.0 (ESP-12E Module)" that is accessed by using the CP210x "USB to UART" port driver available here. Once you've got the board installed, you can browse example code that should work perfectly for your hardware under File -> Examples -> Examples for NodeMCU 1.0. There's a generous selection here, all the way from "Blink" (which, as the "Hello World" of hardware, should always be the first sketch your hardware runs) all the way to "ESP8266WebServer" - which unsurprisingly ended up being the perfect jumping-off point for my own firmware.

After a frustrating and time-consuming detour getting the device to join my WiFi network (it transpires that the "Scan" sketch can find the SSIDs of 802.11b/g/n networks, but to actually connect, it's far better to be on 802.11n-only) it was time to drive some output, which meant more Googling to determine exactly how the L293D "Motor Driver Expansion Board" actually connects to the ESP's GPIO, and what that means in terms of software configuration.

Eventually I cobbled together the necessary knowledge from this board datasheet which talks about D1-D4, and the Arduino documentation for NodeMCU which indicates that these symbols should be magically available in my code. Then I took a tour through the ESP8266WebServer example code to find out what handler methods I had available. At last, I was ready to put it all together - as you'll see in the next blog post.

But before then, a cautionary tale - I fried both the motor shield board and an ESP board while developing this, and I suspect it was due to not being able to resist the temptation to run the whole thing off a single power supply. You can do this by moving this jumper to bridge the VIN (for the chip) pin to the VM (for the motor) pin. But I suspect the resulting exposure to back-EMF and all that grubby analogue stuff is not good for either the ESP chip nor the L293D motor driver on the shield board. You've been warned.

Use 2 separate power supplies here, or just one, but beware ...

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Putting the jumper across here allows using just one of the Vx/GND input pairs ...

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The L293D chip looking worse for wear, having overheated and/or died

(from the eBay listing) this should probably say maximise interference...

Automating heating vents with openHAB, esp8266 and LEGO - Part 2.5; Hardware rework

Working with hardware is fun; working with LEGO hardware is awesome. So before proceeding with the next part of my heating vent automation series, I took the opportunity to refine my vent manipulator, with the following aims:

• Quieter operation; v1 sounded like a coffee-grinder
• Faster movement; to sound like a quieter coffee-grinder for less time
• Lower stack height above floor level; to avoid impeding the sofa-bed mechanism directly overhead

V1 Hardware

As a reminder, here's the first hardware revision featuring a LEGO Technic XL motor and an extremely over-engineered - and tall - chassis.

V2 Hardware

Here's the respun version, which works as well as, if not better than, the original.

The changes:

• The chassis is half as high above the vent surface
• The rack-and-pinion mechanism is centered in the chassis to reduce torque
• The rack is situated lower to reduce flex
• The motor is reduced in size to a LEGO Technic "M" motor (quieter and faster)
• The manipulator clamps to the vent with a Technic pulley wheel instead of a brick, further reducing height-above-floor

Now we're in a really good position to get down-and-dirty with some firmware...

Automating heating vents with openHAB, esp8266 and LEGO - Part 2; Hardware implementation

In the first part of this series I outlined what I'm trying to build - a smart vent on the cheap - so now it's time to build it! Here's what I'm working with - these are "period-style heating registers" as available from my local warehouse-style hardware store. A decorative "vintage" metal plate (scratched to hell) holds a rectangular plastic frame with two pivoting slats sitting in the airflow. A simple plastic slider protrudes through a slot in the metal plate for user control of slat angle.

In the grand tradition of absolutely-ridiculous first hardware versions (check out Mouse v1.0!), I've built this proof-of-concept out of LEGO Technic. In an excellent coincidence, the width of the vent is a perfect fit for the crab-claw-like clamping mechanism I've created, which is fortunate because it requires quite a decent bit of force to move the slider. This gizmo is heavily overbuilt using my best "LEGO Masters" techniques and doesn't flex, warp or bend one bit once it's in position. I'm using an "XL" LEGO Power Functions motor with a worm drive PLUS some extra gear reduction to make sure that:

• I have the torque to move the slider
• The slats won't move unless I want them to (one of the best features of worm-drives); and
• The transition from shut-to-open (or vice versa) takes a while

It might be counterintuitive, but since this solution has no feedback (i.e. to tell it when the slats are truly open or shut) then timing is all I have. Moving everything slowly gives me the best chance of stopping any movement before any hardware limits get exceeded (and expensive Danish plastic starts snapping).

Here it is all mounted up. It sits up about 5cm above the normal vent height, which is obviously less than ideal, but should be fine as the whole assembly sits under a sofa-bed which has copious amounts of space underneath it. The dual pinions (to spread the torque and keep everything level) drive the rack left or right, and the slider is "captured" between the red elements and opens or shuts the slats.

The remainder of the hardware is pretty simple - a butchered LEGO Power Functions cable connects the motor to a standard L293D H-bridge, and thence to the "embedded computer" part of the solution, which I'll talk about next...

Automating heating vents with openHAB, esp8266 and LEGO - Part 1; rationale

It's winter here in Melbourne, and it's a cold one. Combined with the fact that everyone is spending a lot more time at home than before, it's time to start optimising for comfort and efficiency...

I've shared my house's floorplan before on this blog, but this time here it is overlaid with the "schema" of the gas central-heating system, which sends hot air through underfloor ducts into the house through eight vents (or "registers" if you prefer) - shown as red squares:

Now some houses *might* have "zones" implemented, where certain areas of the house are on a physically separated section of ducting and can be addressed and controlled individually. This house is not one of those. I've shown the two *notional* zones we'd probably *like* to have in orange (living spaces) and green (sleeping areas). If you're wondering, we've been advised that for technical reasons related to our heating unit (aka furnace) and available space under the house, a zoned system is not practicable. In any case, it would probably be a bit coarse-grained anyway, as these days I'm working pretty-much 5-days-a-week at home, from the study - the room at the bottom-left of the floorplan.

As such, I would like to be able to control the specific vent in my study, opening and closing it as needed so that it's warm to work in, particularly in the mornings, but also not wasting warm air that is better off being routed to elsewhere in the house in the evenings and on weekends. Also, if the temperature in the study is warm enough, I'd like the vent to shut itself off. It sounds like the height of laziness, but it happens that this vent is located underneath a large couch, so it's actually a major pain to adjust it by hand.

Off-the-shelf "smart vent" solutions have been available for a number of years, from Flair and Keen but they are Not Cheap, don't have any openHAB binding support, don't have stock available and/or don't ship to me in Australia. So it's a roll-your-own situation...