Combination MailBox Minder & Freezer Temp Monitor
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Please be positive and constructive with your questions and comments.

Combination MailBox Minder & Freezer Temp Monitor

by Govner on Mon Jun 03, 2019 1:50 am

Mag Mounted to fridge to display remote, garage freezer temp w/alarm and the second LCD line reserved for mail delivery / retrieval.
KitchenDisplayMag_inset.jpg (104.39 KiB) Viewed 173 times

Hi everyone,

I thought that someone might have an interest in building these.

I have three projects that are finally "packaged" inside enclosures. For me, breadboarding is rather straight forward but when it comes to packaging, I find it a challenge to make the project attractive.

This project is a combination wireless 'Mailbox Minder' and a wireless 'Freezer Temperature Monitor'.

There is a battery-powered, 3 ea AA, for a RFM69 (Adafruit) and an off-brand 328 board (good on low battery consumption). It attaches under the mailbox with high-strength magnets and is triggered by a simple magnetic reed switch when the USPS delivery occurs. When triggered, it sends out a packet message via the RFM69 (Adafruit). It's too far from my mailbox to the ultimate display unit in the home, so there needed to be a 'repeater'. That is, there needs to be another RFM69 in range so that it's listening for the mailbox message and can relay it down the line to the ultimate display unit that is observable indoors. So, instead of just having a repeater unit sitting there waiting for mail, what else might it be doing? Bingo! It can be monitoring something the other 99.9% of the time.

This is the unit placed under the mailbox, held in place by magnets. Sends outside air temp and notice alert when mail is delivered / retrieved.
Mailbox1.JPG (211.77 KiB) Viewed 176 times

In the garage, which is about half way from the mailbox to the indoor, final display location, I have an upright freezer that is (believe it or not) one my wife and I bought when we were in college circa 1969. But, a freezer that's a whopping 49 years old?!! Yeah, it's a good idea to keep an eye on it since the consequences of not noticing a slow thaw when the freezer dies would be costly. Plus, designing Adafruit projects to do this function is kind of poetic. After all, at the time we bought this freezer, computer science was still struggling with the massive size of torroidal core memory and computers 10-times the size of this freezer! So, anyway, back to the project.

The garage RFM69 and, I believe a Metro Mini (Adafruit) monitors the freezer using a readily available Dallas 1-wire temp sensor. I carefully drilled a 1/4" hole through the side of the freezer (where no cooling tubing was routed) and fed the sensor inside. The sketch (.ino) for the repeater listens and relays "You have mail", (which is reset when retrieved). This repeater unit also monitors the freezer temperature and once every minute, it sends the inside freezer temperature to the final destination - The Indoors Display unit. I included a photo of that unit.

The Inside Display Unit -- photo included. It uses the Adafruit RGB LCD, large plastic project box, RFM69 and I believe a Trinket Pro 5V (but any one of several uProcessors could have been used.) It also includes a real-time clock (3231 RTC). I like the clear plastic box so that all the component LEDs are visible and serve as operational indicators. The LCD's first line (16-2 Adafruit) displays the Node # I assigned to the Freezer RFM as well as the signal strength (dBm), the current freezer temp, and the highest freezer temp since 'reset'. (Seeing the temperature swing relates the freezer's efficiency and sooner or later, maybe after its 50th birthday, who knows.

Mag-Mounted to side of indoor fridge but it monitors the freezer out in a garage area as well as the mailbox deliveries.
Colorful_Kitchen_Display_80.jpg (89.32 KiB) Viewed 173 times

The second line of the LCD displays the following : "DDD TT:TT TT:TT". For example, "MON 12:45 13:01". This indicates that on Monday, mail arrived at 12:45 and was retrieved at 13:01. It may not seem like much, but before making a useless trip out to an empty mailbox, expecting to receive my latest Adafruit order, it's nice to know if USPS hasn't arrived. And, I don't have to chase down my sweetheart to see if she's 'holding' and forgot to mention it. Either way, it's a very nice and simple convenience that I would really miss not having now that I've enjoyed it. Oh, yeah, the batteries at the mailbox (also enclosed in Adafruits weather-proof box) lasts for (estimated) 2 months. That's reasonable and with the mag-mount, the batteries are easy to change.

My schematics are available to anyone - as is the code. For people just starting out in these projects, I know that electronic schematics are a challenge. Fritzing is a very handy way to visualize a layout - but not so much at learning anything about electronics. I STRONGLY ENCOURAGE you to be wholy dependent upon Fritzing but rather, seek to learn electronic symbols and meanings. If one is dependent on simply following a depiction of wiring (Fritzing imagery), the project may become operational but the builder walks away having learned very little if anything useful. Seek to learn the principles and symbology of electronics and so when projects get complex or they develop problems, the builder can troubleshoot them based on understanding without having to resort to asking others to solve them. Thanks for letting me add my 2-cents worth. We all need help from our friends no matter how much we learn but we are much happier when we can solve the issue ourselves. It's faster too !! No waiting for someone to answer back. And, finally, who knows what job and/or career opportunities may develop. As a kid, I learned everything I could about electronics and it opened many, many doors and financial opportunities for me. If you're a kid, trust me on this one.

Speaking of help, I have a weak, almost non-existent understanding of how to share my project files here. Since I don't have the time to produce graphics, I can supply hand-drawn (very readable) schematics and diagrams. The code is NOT cleaned up. That is, it's full of commented-out lines used during design and prototyping. It does what I want. You are welcome to improve/change/etc as is the case with open source goodies.

Someone advise me please on how to share better.
For now, check out the pictures. And, also, I have an "Air Quality" and environmental data logger that is completed. I'll post its photos and comments separately.

Imagine it. Build it.


PS: Sorry I don't have the camera gear and setup for Adafruit 'Show & Tell'. If this is not a good, useful alternative, please don't hesitate to let me know and to suggest a way I can help others by sharing. Thank you.

Posts: 126
Joined: Wed Sep 14, 2016 4:42 pm

Re: Combination MailBox Minder & Freezer Temp Monitor

by adafruit_support_mike on Mon Jun 03, 2019 4:38 am

This is a great place to share information about projects. We want people to show what they've done, and what they're working on.

Documenting a project for public consumption is a lot like learning electronics or code: there's theory, but it has to be tied to good old trial and error. The practical side gives the theory context, and the theoretical side turns a bunch of random poking around into a coherent exploration of something. For documentation, the underlying principle is that you're trying to tell someone how you got from the first vague idea for a project to something that stands on its own.

One of the harder parts of that involves reverse-engineering the path you followed from the beginning to the end. It was almost certainly convoluted, marked with failures and false starts. Most instructions omit those, but in the process they lose the context those rejected paths lend to the final solution.

Fortunately you have the ideal test audience available to give you feedback: yourself in about six weeks. That's about how long it takes for the details of a project to fade from memory.

Write what you consider a reasonable short description of something you've done, draw some schematics, or write some code, then put it away and come back to it later. You know you understood it when you created it, and the elapsed time will let you see where you were referring to ideas fresh in your mind instead of things you actually wrote down. Every time you do that, you'll come up with ideas about how to make things easier for yourself next time. After a few rounds of that, you'll find yourself developing a set of techniques and preferences that make up a style.

From my own trial and error, I can pass along two items that are probably the most important I've ever found:

1) Call your shots. Before doing anything.. designing a circuit, writing code, modifying something, fixing a bug.. write a quick description of the situation as it is now, what you're going to change, and what you expect to happen. It's almost physically hard to do, but the payoff is enormous. It's way too easy to fiddle around randomly with no clear goal in mind, only to find yourself tripping over half-implemented fragments of ideas you had a few minutes ago.

2) Keep score. After you've done something, test it and see if it does what you expected. Yes or no, record what it actually does, and why it happened. That's a habit I picked up for writing code, but it carries over to hardware beautifully. Having to document all the little failures like typos, forgetting to change the name of a variable, etc, keep you from just shrugging off bad habits and making them part of your routine.

As a case in point, I don't allow myself to use non-keyed power connectors on prototypes any more. I killed one too many circuits tacking in a quick connection with the wrong polarity, and having to write that down ticked me off to the point of saying, "never again." That irritation justified a whole set of purchases, practices, and prep work that keep me from having to spare two seconds thinking about the power connections while I'm working on circuits. Enthusiasm and dedication are great, but vengeance has incredible staying power.

Documentation is the same. You have to see the things that could use improvement enough times to recognize them, and to set your teeth for fixing them.

Don't worry about greatness or having a high bar to cross. Being able to develop a project and provide barely adequate documentation will automatically put you in the top 10%. If you doubt that, choose any part of Linux at random and look at its documentation. That's the combined effort of people all around the world working for decades, and only a small fraction exceeds the "well I know what I'm talking about" standard. Development and documentation are parallel skills, but they both require practice to develop.

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Joined: Thu Feb 11, 2010 2:51 pm

Re: Combination MailBox Minder & Freezer Temp Monitor

by Govner on Mon Jun 03, 2019 1:54 pm

Thank you for your insight and experiences Mike. Fortunately, I do keep a "lab log" of notes and schematics -- something I've done for over 50 years. As you so estutely articulated, the absence of a project's progress log (including schematics) makes the task of writing a manual very difficult. The last manual I wrote was for my "Rainbow Pedestal" project and that manual was about 50+ pages, including photos. I believe that I posted a copy on Adafruit forums -- yes, I did. Though a first draft, my end users found the manual to be everything they needed I guess. I haven't received any questions on the operation of the Neopixel lighting controllers. So, yes, what you are saying strikes a note of familiarity while at the same time offers new and valuable ideas about how to share projects successfully. Thank you for taking the time to write such a comprehensive summary on the subject. I will do my best to find time to actually complete the task of documenting the project well.


Posts: 126
Joined: Wed Sep 14, 2016 4:42 pm

Please be positive and constructive with your questions and comments.