my bulletted lists of parts are improperly formatted on purpose as a markdown workaround. I can't start a sentence with '#' or it becomes a huge title. So all the parts, which should say "#0 machine screw" or the like say "machine screw #0"

Let's see if the backslash (\) escape works:

#0 machine screw
#2 nylon washer

In a list:

• #0 machine screw
• #2 nylon washer

look at those lists now! thanks!

I wonder if I will miss Markdown when the Rich Editor is implemented.

Presta valve on a soda bottle - yes!

Wow, amazing note. Thanks so much for putting all this so nicely together, @mathew!!!

Still digging in, but quick thoughts:

• The 6-32 screws with # 6 rubber washers look great to me. The readings I've done indicate (I think) that for a two-probe design (like this one), a trick that helps to diminish stray field effects (electric field lines that extend beyond the space between the two screws, and interact with e.g. the sides of a calibration container) is to choose probe size and probe spacing that differ significantly -- i.e., it's best (perhaps) to use smaller screws spaced further apart, or larger screws spaced more closely. Exactly as you're doing in the photos above. I'll likely try 6-32 or a comparable size in my next trials -- as you say, it's the easiest to source in the local hardware store.

• it'd be nice to also come up with a nice way of coupling our temperature probe to the water temp that is as easy to implement and render waterproof as the screws + washers designs shown above. Perhaps adding a third screw, and attaching the temp sensor inside the bottle to the screw (somehow), would accomplish this ...

Thanks!

I bet the thermal coupling with a temperature probe could be easily accomplished with some heatsink thermal paste connecting the temperature sensor to a screw through the cap.

That said, I'm strongly in preference to building more components around the stopper-based design and will focus on that, and conductivity setups that fit through the stopper, along with a thermistor.

While I'm sensitive to this use case of rapidly deployed DIY conductivity, I'm more interested in a more rigid bottle platform supporting a variety of sensor configurations.

As a thin piece of HDPE, the cap is a very confining component on top of a very confining (22mm wide) housing size. It seems to me that the ease of setting up a screws-through-the-cap demo has been driving this design, while it introduces a host of other problems without satisfactory solutions:

My primary concern is the rigidity of the internal riffle mount and security of wiring between sensor and riffle. The cap and the riffle can't be rigidly connected because sensors take up the whole cap surface. So the riffle must be mounted independently, and space given to twist the wires between riffle and bottle. The wires are inherently going to get yanked around and that is a reliability issue.

Putting screws through the cap solves a single sensor use-case at the expense of all others since we haven't identified any way to put other sensors through caps at the same time.

If we're going to do screws-through-the-cap as a default configuration suggestion, I'm skeptical that 6-32 screws are worth using despite their ease of availability. 6-32 screws are easy to get, but the ease of working with them stops there:

• Its hard to make properly sized holes for them, as the cap material is hard to drill out and too wide to be poked through with a tack without dramatic warping.
• The screws are awfully crowded in the cap, especially trying to keep the ring terminals from touching.
• Its hard to fit the screws and the ring terminals in a way that doesn't effect the cap's threads. The screws are big enough that they warp the surface of the cap and create flexion during tightening and loosening, a structural issue that might become a calibration issue.

How many sensors can a Riffle monitor gracefully?

Considering that the typical sensors that might be used are cheap and maybe unreliable, does it make sense to have three $2.00 temperature sensors as replicates? Conductivity sensors are even cheaper (a couple of screws), and notoriously unreliable, so why not have three of them on each Riffle deployment?

If the Riffle and batteries are in a water bottle, can a single cable bundle pass to a separate enclosure that is a sensor pod? The pod could be a simple container of tough material (e.g., PVC) that is easy to drill and seal. The pod could bristle with replicate sensors. This gives each Riffle deployment a rigorous test of the precision of the sensors used, in addition to redundancy in case of failure.

But I guess that sensor pod could be just a little bigger and the Riffle could be in there.

I have once again convinced myself to abandon the water bottle.

Sorry.

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To sum: @cfastie will be using a Nalgene bottle, @mathew will be using stoppers and pop bottles, and @donblair will be using screws and water bottles, because the riffle can fit in almost anything.

Yes Nalgene. Remember when BPA drove all responsible mothers and other tree huggers to abandon Nalgene water bottles? I have a box in the shed full of old Nalgene bottles.

Hoarders: 1
Normal people: 0

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That's how i keep score too @cfastie !

Some ideas:

I love the presta valve idea (I used to work in a bike shop, and we threw many of these away each day from flats). I wonder if having a large metal post nearby would interfere with the conductivity measurements?

I'm jumping into the middle of the stopper vs. cap discussion without knowing much, but I like the flexibility of using caps, because of the fact that you can adapt the design to use with larger bottle openings, like the nalgene. Have you experimented with a design that has only cables passing through the cap? Cables could connect to whatever sensors or antennas the deployment is using, if fitting all the sensors on the cap is limiting.

For temperature sensors, do many uses require the sensitivity of having the sensor to be outside of the bottle? Because otherwise the temperature sensor could be attached to the inside of the bottle, assuming the bottle comes to equilibrium with the stream temperature fairly quickly, saving space on the outside.

Goodwill and other thrift stores can be great places to look for old nalgene bottles, and other wide mouthed plastic bottles. Sometimes these come from local losts-and-founds.

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@pdhixenbaugh, we have experimented with putting cables straight through the cap, and it hasn't been successful. the plastic (HDPE) of caps is very hard to glue to and can't be sealed with adhesives or sealants, it has to be a mechanical seal with gaskets or rubber washers.

there are ways to do it mechanically involving custom hardware, such as this Blue Robotics cable penetrator ($4): https://www.bluerobotics.com/product-category/parts/connectors/

While that part is both open source AND cheap, its a custom part from a single supplier. A bunch of those in the lid of a Nalgene bottle would make for a nice and easy-to use system though.

Any hollow bolt can be a cable penetrator. These cost $1.20 apiece, but you also need two nuts and rubber washers. The hole is only 2.3 mm in diameter, so not many cables can pass through each one. Those nice Blue Robotics penetrators have a bigger hole (about 5 mm?) and better facility to glue the cable in.

http://www.mcmaster.com/#91979a846/=112xdbj

For many uses a temperature sensor can be inside the enclosure, but some uses might call for more contact with the medium. Waterproofing the temperature sensor for external use is a separate challenge.

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I've looked at those vented set screws-- their vent holes are tiny but they might work.

I'd like to try sealing one with glue. My suspicion is that its going to be hard to get enough glue in to get a good seal, and that the glue will fill the hex and make removal hard. At a buck a piece its hard to complain and definitely worth a shot.

These M12 vented screws give another .2mm of space for wires (2.5mm) and a knurled end for better purchase when turning. I'd feel comfortable completely filling the hex-key head with glue on one of these: http://www.mcmaster.com/#93235a371/=112yxyn but at $6.75 not including washers and nuts, they can't beat Blue Robotics.

McMaster isn't known for cheap hardware. They just have the best catalog. A better deal is probably available elsewhere and this is a more standardized industrial part.

Threaded lamp pipe. 3/8" OD. $3.27 for 8 pieces

http://www.homedepot.com/p/Westinghouse-8-Assorted-Nipples-7015000/204836020?MERCH=REC-_-PIPHorizontal1_rr-_-204836053-_-204836020-_-N

and nuts, $2.77 for 12 pieces

http://www.homedepot.com/p/Westinghouse-12-Solid-Brass-Hex-Nuts-7017200/204836028

This makes six cable penetrators for: $3.27 + $2.77 + rubber washers + glue for sealing the wires inside the pipes

But regular 3/8" hex nuts are cheaper and should work better.

Lowes has brass nipples, eight for $2.98 http://www.lowes.com/pd_46816-1811-905L_1z0vitnZ1z135ut__
Or you could use the threaded tube from those discarded Presta valves.

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I ordered these lamp rods, some of the threaded cable penetrators, and some silicone tubes to the pdx office. The blue robotics folks say steep bulk discounts (and custom colors!) are available, but we'll check out how these work side by side

those lamp rods! mic drop

I've toyed with brass nipples, but most valves expect to be screwed into a thicker material and have tapered threads (labeled NPT usually). You can't put a nut on a tapered thread, unfortunately.

I don't follow. Are you saying they will work, and drop the mic in a "hellz-yeah" way? or are you saying they won't work and drop the mic like a Nintendo controller after losing at Tetris?

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I'm excited about lamp rods.

sorry, I was confusing the 'lamp nipples' with air hose nipples and the like:

My one concern is that brass parts will corrode faster than stainless. don't see any stainless lamp pipe on a quick look though.

The lamp pipe looks very close to an ideal solution, but... lead is added to brass to make it more machinable. If the brass isn't certified for use in Californian plumbing, its probably 1-3% lead with high lead motility in electrical grounding and water contact uses. Both outcomes are likely in a long-term underwater or underground sensor installation.

I was hoping that RoHS certified lamp components for the EU might be lead free. but copper alloys have an exception under RoHS.

I think this same lead problem applies to the presta valves as well.

I've only seen light steel as a replacement for brass in lamp pipe. I haven't seen stainless steel or other alternative non-corrosive material. Light steel seems like a bad option because it corrodes readily, but painted steel has a good track record in marine uses. I'd rather use a completely non-toxic material like light steel and coat it in a tough enamel paint, like nail polish.

Threaded lamp pipe comes in zinc plated steel, but I don't think we will find stainless. Here are two bulk suppliers of nipples:
http://www.antiquelampsupply.com/product/1731_18-ip-steel-all-thread-nipples
http://www.grandbrass.com/ShowItem.cfm?ItemNumber=NI1-1/2X1/8&session.currentcategory=Nipples&session.currentsubcategory=Nipples(pre-cut)

A 1 1/2 inch long nipple costs $0.15.

Another problem is that the threads are non-standard (27 threads/inch) so you probably have to use the skinny nuts made for lamps. Standard 3/8" nuts can be 16, 24, or 32 threads/inch.

The thicker lamp nuts are $0.05 apiece:
http://www.grandbrass.com/ShowItem.cfm?ItemNumber=NU234WZ&session.currentcategory=Nuts&session.currentsubcategory=Nuts

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These 18650 keychain battery holders just arrived. They're great:

Tried drilling through bottle cap, then making the hole really jagged using an awl. Then a pen tube through a rubber stopper, thick layer of silicone sealant on outside. Pressed it snug, then backfilled on the inside and let it cure.

The fact that the silicone goes through the cap and flares on both sides makes it work, even though "technically" it doesn't adhere to this type of plastic.

Technically, you can't glue plywood with fiberglass , but it works in practice. And it looks like this method of passing wires out of a soda bottle works in a similar way.

This test was just with a pen with standard plug in it. Assuming it will work to pass wires through the tube and then backfill with more silicone. I'll try that next to make official, but just seeing if I could improvise something with what I had.

FYI, we got the lamp parts in the mail today, and they have a lead warning on them:

Possible we can source parts that don't contain lead, but something to consider in modelling a DIY solution that people might make from local hardware store, espec if we assume not everyone will go through the trouble to track down lead free version to throw in the creek.

hasn't lost a drop!

for completeness' sake: Check out @edwardmallon's note: https://publiclab.org/notes/donblair/09-08-2015/rubba-stoppaz#c13904

Chris fastie's Nalgene Sub: https://publiclab.org/notes/cfastie/03-11-2016/nalgene-submarine

Again with these blue robotics connectors. https://www.bluerobotics.com/product-category/parts/connectors/

dot