Author Topic: Tiny TH Mote  (Read 12177 times)

joelucid

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Re: Tiny TH Mote
« Reply #15 on: August 27, 2015, 11:15:29 AM »
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I suppose, where you live, heating the room is useful   ;D

Absolutely! That's why I like the si7021 so much: it actually contains a small heater ...

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The Si7021 contains an integrated resistive heating element that may be used to raise the temperature of the
sensor. This element can be used to test the sensor, to drive off condensation, or to implement dew-point
measurement when the Si7021 is used in conjunction with a separate temperature sensor such as another Si7021
(the heater will raise the temperature of the internal temperature sensor).

TomWS

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Re: Tiny TH Mote
« Reply #16 on: August 30, 2015, 01:51:46 PM »
To package the Tiny TH Mote I needed to make a worthy 'enclosure'.  While I don't have my full complement of woodworking tools at my current digs, I was able to cobble together a useful collection of tools to make something close to what I had in mind.

In the attached photo, you'll see a composite of the progression from start to 'almost' finished (finished comes in the next posting since this photo is too large to include anything else).

The first panel shows a couple of scraps of hardwood, one Cherry, one Walnut, and the tools I planned to use to transform these scraps.  The small drill is used to drill a pilot hole to keep the two forstner bits aligned, since I had to drill these holes from opposite sides of the workpiece.  These are not drilled all the way through, but far enough to create a reference counter bore for later. 

The next panel shows the workpieces cut out using the hole saw.  I would have liked to go smaller diameter, but the scrap wood was too thick and the aspect ratio would have been wrong.  In any case, pretty rough looking at this point.

Next two panels show the mounting of the workpiece in my 'lathe'.  I had to go to a hand drill rather than drill press since the thread on the 'chuck' required running the turning  counter clockwise.

The next panel shows the first pass roughing to general shape and then the final panel shows the finished pieces with the center bushing still intact.

More following...



TomWS

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Re: Tiny TH Mote
« Reply #17 on: August 30, 2015, 01:55:19 PM »
Here are a couple of close ups of the finished pieces.  The circuit board will be covered with some screening, but I like the looks of it this way  ;)

Enjoy.

Tom

WhiteHare

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Re: Tiny TH Mote
« Reply #18 on: August 30, 2015, 03:44:23 PM »
Very creative!  I  like how you even made a temporary lathe out of your hand drill.

The device electronics and PCB are so tiny that I had imagined you would be putting them into a shell that was only just a hair bigger than they were.  The approach you took instead looks very nice though, and it's a clever way to keep your antenna wire straight and vertical, like a plumb-bob. 

Would it make any sense to give the PCB a larger air gap (or possibly some insulation) all around to mitigate effects like thermal mass and/or self heating?  Or are those likely to be so small it wouldn't matter?

Also, am curious: if you ever needed to reprogram it, would you be using OTA wireless upload programming , or as during development do you have a jig with pogo-pins that fits into the depression for it to physically dock with?
« Last Edit: August 30, 2015, 04:01:01 PM by WhiteHare »

TomWS

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Re: Tiny TH Mote
« Reply #19 on: August 30, 2015, 04:12:26 PM »
The device electronics and PCB are so tiny that I had imagined you would be putting them into a shell that was only just a hair bigger.
Ultimately that's the plan, but, as I said, you can see in the photo showing the rough turning the tool I used to 'cut' the profile - a file with a flat and a partial round side.  When I get back to my workshop I'll be able to turn a decent piece out of a properly thicknessed piece of wood.
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Would it make any sense to give it a larger air gap all around to mitigate effects like thermal mass and/or self heating?  Or are those likely to be so small that it doesn't matter to you? 
I don't anticipate a problem with this, certainly not self heating - this thing draws virtually no power!  The sensor is an SI7021 which you can see pretty well in the Cherry photo (U2) and it's positioned so that normal convection airflow will affect it.  I want to measure room temperature and that includes the walls.  I don't need instantaneous response.
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Also, am curious: if you ever needed to reprogram it,
Why would I need to do that?  8)
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would you be using OTA wireless upload programming , or as during development do you have a jig with pogo-pins that fits into the depression for it to physically dock with?
For the moment, it'll be pogo-jig reprogramming until I get Joe's bootloader...  The module is only friction fit into the back cavity so pulling it out to reprogram is trivial.  The package worked out pretty well in this regard.  The PCB is 26mm diameter, but leaving the holding tab 'residue' on the edge of the PCB allows it to friction fit into a 27mm hole.  So the wooden piece is drilled to 26mm in the front and 27mm in the back leaving a ring that acts as a stop when inserting the PCB from the rear.  Cutting the slot for the antenna wire was easy with a thin pull saw.

I should have mentioned that the pictures show a magnetic clip holding the end of the antenna wire - that clip is simply attracted to a drywall screw in the wall.  It turns out, with the thin cavity behind the battery (and the fact that the magnet sticks to the battery), I just need a small super magnet to attach the unit to the wall without needing the clip.    A 15mm diameter magnet will be perfect!

Tom
« Last Edit: August 30, 2015, 04:18:47 PM by TomWS »

luisr320

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Re: Tiny TH Mote
« Reply #20 on: August 30, 2015, 04:46:27 PM »
Recently I adapted my CNC to become a 3D printer. You could easily make any type of  enclosure in ABS or PLA. But nothing compares to a good handmade workmanship. Very nice.
« Last Edit: August 30, 2015, 05:44:48 PM by luisr320 »

TomWS

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Re: Tiny TH Mote
« Reply #21 on: August 30, 2015, 05:57:31 PM »
Recently I adapted my CNC to become a 3D printer. You could easily make any type of  enclosure in ABS or PLA. But nothing compares to a good handmade workmanship. Very nice.
LOL, did I mention that I have a CNC router at home?   ;)

Although, in this case, the wood lathe is much more appropriate.  The CNC router will be used to make the enclosure for the Thermostat variant of this Mote (it has an OLED display and, no, it won't run on CR2032  :)
Tom

TomWS

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Re: Tiny TH Mote
« Reply #22 on: September 11, 2015, 04:28:25 PM »
Stepping up to the before and after challenge set down by joelucid in his thread https://lowpowerlab.com/forum/index.php/topic,1269.0.html,
here is the the promised before/after photo of the Tiny TH Mote.  The two circuits are functionally and electrically equivalent, just packaged differently  :)

Enjoy.
Tom

luisr320

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Re: Tiny TH Mote
« Reply #23 on: September 11, 2015, 06:46:09 PM »

No seriously, do you intend to make them available trough Felix store? I would be interested in acquiring some. And they would be a nice addition to the Moteino family. Can you connect anything to them, like some external sensor, or only those onboard?

TomWS

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Re: Tiny TH Mote
« Reply #24 on: September 11, 2015, 08:24:16 PM »
No seriously, do you intend to make them available trough Felix store? I would be interested in acquiring some. And they would be a nice addition to the Moteino family. Can you connect anything to them, like some external sensor, or only those onboard?
I added the design files to the opening posting.  You can build as many as you want.  Not much room for expansion, however.

Tom

TomWS

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Re: Tiny TH Mote
« Reply #25 on: September 13, 2015, 11:00:47 AM »
I've added the ListenMode extensions to my RFM69_ATC library, including two new example files demonstrating how you could use the extensions in both Node and Gateway functions.

The new branch is at https://github.com/TomWS1/RFM69_ATC/tree/ListenModeExtensions

Enjoy,
Tom

WhiteHare

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Re: Tiny TH Mote
« Reply #26 on: September 13, 2015, 12:18:04 PM »
Thanks!

What's the difference between the ATC and ATC_WL examples?   I guess WL are the versions we should use, as they were the ones you just today uploaded.
« Last Edit: September 13, 2015, 12:36:41 PM by WhiteHare »

TomWS

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Re: Tiny TH Mote
« Reply #27 on: September 13, 2015, 01:07:44 PM »
Thanks!

What's the difference between the ATC and ATC_WL examples?   I guess WL are the versions we should use, as they were the ones you just today uploaded.
'WL' versions are 'with ListenMode'...  ;)

Tom

TomWS

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Re: Tiny TH Mote
« Reply #28 on: September 23, 2015, 09:08:22 AM »
I've added the ListenMode extensions to my RFM69_ATC library, including two new example files demonstrating how you could use the extensions in both Node and Gateway functions.

The new branch is at https://github.com/TomWS1/RFM69_ATC/tree/ListenModeExtensions

Enjoy,
Tom
The ListenModeExtensions branch now has the update to remove the inter-packet delay from sendBurst().

Tom