Crinkles NFC Diaper Inventory Management - Complete Guide V1


All Puns Intended
Est. Contributor
  1. Diaper Lover

Blaincorrous here with a complete guide to one of my passion projects over the last few weeks: automating diaper checkout with the iOS/iPhone app Crinkles and commodity NFC tags, widely available at your friendly neighborhood... uhh... Amazon distribution center. I'm sure you can find in other places.

So, allow me to present a complete guide to setting this scheme up for yourself.

I don't want to dissuade you from tackling this project because of your perceived lack of technical skills. I'm dead serious about this. I'll walk through all the details of setting this scheme up for you, including any troubles, costs, or insurmountable limitations I encountered as I iterated through my project. More likely than not, you will learn something new you can use in ways I hadn't thought of. And I've tried to compress a few talking points behind spoilers in anticipation of some discussions, but so as not to bog down the guide too much. There's not that much that's tedious, but mostly, I want this to be a fun way to scratch our OCD while engaging in diaper fun.

By the time you are done, you will have inventory management of your diapers one tap away from you at all times. All the changes tracked and your inventory up to date at all times.

The Setup

Crinkles is a free iOS app, linked here for your convenience. It tracks the use of any number of diapers you could add to your stash. It's preloaded with many popular, common diapers on the market, and you can add a custom entry for anything. You can add stock as it comes in, track changes that automatically decrease your stock, and get metrics on what you use and how long you wear them.

As far as I can tell, the developer appears to be a member of the community with a public facing business possibly created just to support this app and the legal necessities, but here's their privacy policy if you would like to review for yourself. I trust the intentions behind this app, but I leave it up to you if you want to err on the side of caution. I personally believe you will be no more open to threats than you are using ADISC or its Discord server, which is to graciously say I implicitly trust the protection and security @Moo has in place or I wouldn't be here.

NFC tags are a close cousin to RFID tags: they both work on radio frequency to exchange data with a reader and to write durable information to the tag for later retrieval. They are used in a variety of places you might have started to notice. For example, in some malls , you might see an inconspicuous white sticker next to an access corridor. Those are used by security services to enforce their contract with the property management company. By requiring guards to scan them, they can prove they're doing their rounds to the satisfaction of the management.

And finally, the Shortcuts app (also called "Siri Shortcuts" in some contexts) is an Apple aquisition from a few years ago. Since the idea entered my head, I've been obsessively looking for ways to leverage a technology stack that allows me to make my diaper inventory clear and easily manageable. After I started playing with the iOS Shortcuts app to automate pulling driving directions from my calendar when I connect to my car, I wondered what other possibilities existed. Tracking diapers seemed like a natural fit.

Let me be clear that I'm not putting an NFC tag ON each individual diaper. That would be cost prohibitive in this context. If some ABDL manufacturer wanted to find an economical way to take that step and make their own app to go with it, I think it would be very cool, but they're probably looking at the same limitations and the increase of cost per-diaper that I am. It would be vastly more cost efficient to print QR codes on packaging for check in and QR codes on the diaper for checkout, but even then, it's another freaking QR code in the world that could be done via other means.

Let me lay out the limitations up front before the rubber panties meet the road:
  • You can't bring in new diapers with NFC taps. You have to manually add them to the Crinkles app.
  • You can't have multiple items in a change like a diaper AND a booster and track it unless you use an entire tag for just that combination. I recommend those changes be manually managed.
  • Alternatively, you COULD simply scan the tag of the booster first and THEN scan the tag of the diaper being used.
  • If you trigger a change for a diaper that's out of stock, Crinkles will still log the change as if it were in stock.
  • Alas, I couldn't get this to work with an Apple Watch, which would have been even more convenient.

The Cost

Assuming you have an iPhone model that's keeping up to date with the latest releases of iOS, you have the biggest expense already paid for. You could do this with an iPad as well, but you will find that harder to manage than an iPhone, just by virtue of its size.

Outside of that, here's the project costs for each type and size of diaper in your collection, based on my costs before tax:
  • One 1 inch diap...diameter (US Quarter-sized) NFC tag - $0.3663
  • One 1 inch diameter printer label - $0.0101
  • One US Quarter-sized (1 inch diameter, of course) coin protector - $0.0999
    • Amazon
    • Comes with a case for storing. This is definitely a good thing for storing unused but already setup tags.
  • 0.5 inch square of heavy duty acrylic mounting tape - $0.0124
Please note: I have included links because these fit together perfectly and enable certain functionality that works for me. I'm not making money off these links nor am I promoting or have an interest in these products, the linked apps, or even fricking Apple over any other equivalent products. I'm sure there's other ways to do all this with Google Sheets or something else, but that's going to be even more involved.

Of course, no one is going to sell you one of each and ship it, so you will always buy in quantity, but the total cost for me to realize this part of the project was less than $60. You could probably do a lot better than that if you wanted to, and some of this was bought for other purposes. Again, it's only an issue of volume. I got 30 tags, 100 coin protectors, 1575 labels, and 30 feet of mounting tape. You will end up with more than you probably need for your collection, but this will allow you to expand the digital integration as new diapers land on yourself.

The Crinkles App

First, I'm going to assume that you can use the Crinkles app to add your collection to the database. If you need assistance with that, I can write that up below. Crinkles only exposes shortcut procedures for adding changes to your log and thereby tracking diapers out. This only lets you track diapers as you use them, but adding diapers to your collection should be a breeze.

So, go add your diaper collection to Crinkles, creating custom entries as needed. (Be careful not to assign a brand to a custom item that's not on the brand list. This is impossible to correct later, or at least I didn't find a way.)

The NFC Tags

Next, let's prep our NFC tags.

1 inch diap... dammit, I did it again... ahem...

1 inch diameter is a clear commonality of the physical parts, and what we're going to do with them is fairly obvious: we're putting a label and tag in each protector and mounting them where they will be scanned. But, if you'll indulge me by expanding the below spoiler, I will explain my method to call out what I think is an optimal practice: Leaving one half of the protector on your storage and swapping out tags as your active inventory shifts.

  1. Print or write the names of all the diapers in your collection on labels while they are on the label sheet. You should have a convenient list of your diapers on the Crinkles app to facilitate this now.
    • If you want to track different sizes or versions of diapers, you will need a separate label (and tag, case, adhesive) for each, so make a label for each.
    • Follow the directions for the label paper for printing templates, but a word of caution: you will probably go through a few pages worth trying to get the alignment right, especially at this small a size. I'd just as soon write them with a pen after my experience trying to print. But if you want pictures or to make it extra neat, printers are an option.
    • And yes... you could get a roll of 1 inch circular labels for garage sales if you're just going to write on them.
  2. Open a coin protector and put the label in the smaller "male" side, sticky side AWAY from the protector. I linked specific coin protectors above because they had some ideal characteristics. The way they fit together does three things.
    1. They have a "male" and "female" side. The label should go inside the male side (where there is a lip that will fit inside the other female side of the protector). Again, that's the counterintuitive NON sticky side against the INSIDE of the MALE protector.
    2. You CAN put the label on the tag first, but if you're OCD, you're going to be disappointed with your ability to align it perfectly. Into the protector first will save you the headache and heartache.
    3. They have a lip where you can easily separate the male and female sides of the coin protector. When we mount them, we will mount them with this lip pointing UP, so we can easily find the lip, separate them, leave the female side behind, and change the male side to a new label/tag/protector set.
  3. Take an NFC tag and press it into the male side of the coin protector and into the sticky side of the label. The fit should be fairly tight, but not overly tight.
  4. Cut a 0.5 inch square of acrylic mounting tape with sharp scissors and affix to the OUTSIDE of the FEMALE part of the protector. Leave any protective film attached until you mount this, if doing in batches.
  5. Mount the female sides of the protectors with the separation lip facing up or away from you on your diaper storage bins, on your diaper shelves, on your changing table, or anywhere else you store your diapers just before use. Ideally,.
    • Be aware of the type of adhesive you use. I'm using heavy duty acrylic "jelly" mounting tape and primarily mounting on fabric storage bins. This adhesive can do a real number on painted surfaces and is practically permanent on most painted, drywall, or wallpapered walls and surfaces. You might need to consider alternatives in your case, like foam Command strips, which may increase your cost.

One other thing to consider, you should reserve a few tags for your diaper pail or other trash cans. You will be able to scan that tag to tell Crinkles that you're not presently wearing anything, IF you want to track that state... and I suppose IF you ever find yourself in that state again...

The Shortcuts (Automations)

Now, open your Shortcuts app and choose the Automation section from the bottom of the screen.

You need to do this for EACH tag you’ve created. This part is a little time consuming, and I intend to rework this method entirely, but for now, this is how it works.
  1. Tap the + to create a new automation. You need to choose personal automation and then NFC.
  2. Tap Scan and touch the phone to the tag you’re writing (keeping other tags away from your phone to avoid confusion). After it accepts it, name the tag with the name of the diaper. That will make the automation easier to keep track of.
  3. Next are the actions. I’m recommending two actions: A “Vibrate Device” action, and then the “Add a New Change” action. Add them in that order by searching for them with the Add Action button or the search field at the bottom.
  4. The Vibrate action needs no setup, but you will need to set the Change action item to specify the diaper of the NFC tag. (While you’re here, I suggest you also tap the little arrow to open the Change and choose to Show When Run, to give you an added confirmation, but that is technically optional.) Once that’s complete, hit done.
  5. Finally, you will get a summary of the automation you’re about to create. I recommend turning Ask When Run off and hitting Done to complete the tag.
Great, you have ONE tag done. And if you’re anything like me, you have a lot of tags. You can streamline some of this by creating all the automations with blank Action sections to get all the scanning out of the way and set up the actions at your leisure. You can also copy and paste the Vibration and Change actions by using the little icon next to the action block, or you can simply set the Actions as favorites in the Action picker.

That’s enough to do inventory tracking. When you tap tags you registered and set up, it will log the diapers you’re using.

If you want to create the disposal tag and log when you’re not wearing with a tag on your diaper bin, it’s not necessary for inventory (what does Crinkles care if you’re wearing the same diaper for 3 weeks), but you can do so in a similar procedure. It’s just a little more complicated to get the Not Wearing state into an action.

Open Crinkles, choose the Changes screen, and tap the ‘i’ next to a Not Wearing change. Create the Siri Shortcut to log not wearing. Then, go through the above procedure to register the NFC tag you’ll mount on the trash can. The only difference is that instead of creating a Change procedure, you can copy the action from the shortcut you had Crinkles create, or you can just reference that Shortcut with the “Run Shortcut” action.

I had to make a few choices. If you start poking around in Shortcuts, you might think there’s got to be an easy way to take the details of the diaper directly from the NFC tag and pass it to Crinkles and make use of refactorable procedures, one shortcut, and one automation. Well, let me tell you… I went through a FUCK TON of testing trying to find a way to preserve the datatype that Crinkles uses to represent a change and utterly failed to recreate it. I only ever succeeded in making hardcoded actions for each diaper type. Other little odd things here and there have been integrated into this method, like adding a Vibrate action to each automation to give quick feedback on scans and silencing extraneous notifications. My next version is intended to use Google Sheets and skip Crinkles entirely, but that’s going to take some more work and time on my part. However, I should be able to create a system that also handles incoming stock and exposes better opportunities for refactoring and efficiencies in setup.

I do some other clever things with this. At the time my phone prepares for sleep mode, it asks me what diaper I'm wearing tonight. Then, when my morning alarm goes off, it automatically logs a Not Wearing, because I always immediately take it off.
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