NikosMy first prototype PCBs have arrived!
My first concern with the PCBs was to see which case they would fit in. And by case I mean acrylic cosmetic lotion jar, like the ones you can see below.
The distributor's website only listed their internal volume (Left 5ml, right 3ml) and their external diameter, so I had to calculate the internal diameter by counting pixel on available photos and intrapolating from the external diameter. I also had to guess a margin because these jars tend to get narrower towards the bottom.
The 5ml jars are only a couple mm wider than the 3ml ones, but they are considerably taller so I'd prefer the PCB to fit in the 3ml jar. And it did.
It fits so well that it can't move at the bottom. Once the battery holder is soldered on the underside of the board, there should be half a mm or so of marginal space.
I like these jars because of their very low cost (€0.35 for the 3ml ones, €0.21 for the 5ml ones) but also for their ease of use - just a screw-cap to open/close them. No screwdriver. However, they are certainly not waterproof, and I need them to be.
Since these temperature loggers are going to be inserted in the sand and left there for anywhere between two and six months, regular opening won't be required. To keep costs low, I'd prefer to add a small amount of food-grade silicone (so no contamination will be caused to the environment) on the thread before screwing the cap on. After the data logger is retrieved, the seal can be easily broken open and discarded. The loggers will have to wait for at least 12 hours for the sealant to cure before deployment. Luckily, deferred start of logging should be an easy feature to implement.
Next I plan to hot-plate solder a couple of boards and begin programming them, but also to perform some testing on the sealing process mentioned above and the results in water-tightness.
Discussions
Become a Hackaday.io Member
Create an account to leave a comment. Already have an account? Log In.
I really like this project, especially the use of these jars. I'm using similar jars for a project of mine #TritiLED . The 3g jars I ordered are roughly the same external size as the 5g, they just have an indent in the bottom taking up space (2ml of space, presumably).
I can't tell from your images if they 3g versions you have are shorter than the 5g's - I think from the text that they are. Can you tell me how tall the two versions you have are?
Are you sure? yes | no
Thanks! I didn't notice any extra internal width near the bottom. Sorry but I'm in the middle of a 6-week trip and only have the a 3ml one with me. The 3ml ones were about 3-4mm shorter than the 5ml ones but still tall enough for the coin battery and circuit plus a bit extra.
The 5ml ones were about 2mm wider on the inside, so the biggest difference is the height. With no published specs and so many no-name manufacturers I wouldn't be surprised if you got different jars though.
I like your #TritiLED project, very useful information I hadn't seen before! (now I feel like I sleep-read your posts and copied some of the ideas)
Are you sure? yes | no
Thanks for the info! You definitely found "better" 3g cases: I'll look around for some similar ones.
I've been checking out your project, too. I have some old ideas for long-term loggers that could make use of some of your ideas.
Good luck on the contest; this is a very cool entry.
Are you sure? yes | no
I put some play-doh in the 3ml vase to give you an idea of the shape. A US dollar quarter just fits in but won't go below the middle, so there is a slight narrowing towards the bottom. The CR2032 holder goes all the way down though.
https://hackaday.io/project/27560/gallery#7a9c4491fc1f555ae9af13240af72c6e
https://hackaday.io/project/27560/gallery#d502536b966bbed846a3ece229fd8e73
You're welcome to collaborate if you think this can work for your logger ideas. I'm also trying to keep the option for "expansion boards/shields" open but don't have any plans for that of my own.
Good luck with the coin cell challenge too, I found your project has a lot more technical detail which is very insightful!
Are you sure? yes | no
Thanks for the pics! I definitely have different 3g jars - I'll look around for ones like you found.
I also ordered some 25x1mm rubber o-rings to try sealing the jars in a re-usable way. I guess cracking glued jars like a nut isn't so bad since they're cheap, but it would be nice to have another option, too.
Are you sure? yes | no