IoT-Enabled Mailbox Lets You Check Your Mail Without Leaving Your House

A mailbox with a solar cell on top

Whether you live in an apartment downtown or in a detached house in the suburbs, if your mailbox is not built into your home you’ll have to go outside to see if anything’s there. But how do you prevent that dreadful feeling of disappointment when you find your mailbox empty? Well, we’re living in 2022, so today your mailbox is just another Thing to connect to the Internet of Things. And that’s exactly what [fhuable] did when he made a solar powered IoT mailbox.

The basic idea was to equip a mailbox with a camera and have it send over pictures of its contents. An ESP32-Cam module could do just that: with a 1600 x 1200 camera sensor, a 160 MHz CPU and an integrated WiFi adapter, [fhuable] just needed to write an Arduino sketch to have it take a picture every few hours and upload it to an FTP server.

A pile of components making up an IoT Mailbox
The components inside: a solar cell, battery, power controller, LDO and ESP32-Cam module with WiFi antenna

But since running a long cable all the way from the house was not an attractive option, the whole module had to be completely wireless. [fhuable] decided to power it using a single 18650 lithium ion cell, which gets topped up continuously thanks to a 1.5 W solar panel mounted on the roof of the mailbox. The other parts are housed in a 3D-printed enclosure that’s completely sealed to keep out moisture.

The enclosure had to be made from a material that does not degrade in direct sunlight, which is why [fhuable] decided to try ASA filament; this should be very resistant against UV rays, but proved tricky to process. It warped so much during cooling that the only way to get a solid piece out of the printer was to enclose the entire machine in a cardboard box to keep it warm inside.

The end result was worth it though: a neat little extension on the back of the mailbox that should keep sending photos of its insides for as long as the Sun keeps shining. The camera should also give a good indication as to the contents of the mailbox, allowing the user to ignore any junk mail; this is a useful improvement over previous IoT-enabled mailboxes that use proximity sensors, microswitches or optical sensors.

35 thoughts on “IoT-Enabled Mailbox Lets You Check Your Mail Without Leaving Your House

  1. Lithium batteries for outdoors projects are a pain in the rear, because most types can’t be charged below freezing. if it stays below freezing for 4-5 months a year, you basically have to design the device to charge up in the fall and either hibernate or use so little power that it survives on the last charge it got.

    The reason is, you have to drop the charging rate to ridiculously slow (<0.02C) or else you get lithium plating on the electrodes, which leads to permanent capacity loss and dendrite growth, which leads to breaching the separator, which leads to a battery fire – so your mailbox may torch itself after a while.

      1. Their TLI series does appear to have the ability to charge at negative temperatures, but when you look at the datasheet it reveals the exact problem I was talking about:

        https://tadiranbat.com/assets/tli-1550s-rev-d-june2020-1-.pdf
        “Max Charge Current @ -20 to +50 °C 100 mA”
        “Max Charge Current @ -40 to +85 °C 20 mA”

        Only incredibly slow charging rates allowed. If you get 1 hours of full sunlight limited at 100 mA into a 3.6 Volt cell, you’ve got a whopping 360 milliWatt-hours of energy that day, and you can only utilize 24% of the capacity of your 1.5 Watt solar panel. However, because of this problem, most lithium solar charger ICs with temperature monitoring actually just shut down below 0 C because of this problem.

        1. Also, “For more than 2 cells in parallel, maximum charge current shall be limited
          to 250 mA for the whole pack.”

          So if you want more than 2 Amp-hours of capacity, you can only charge at less than 0.10C.

  2. Fun fact: if you live in the USA the post office will actually email you images of your physical mail each day. You just need to sign up for it. The service is called “Informed Delivery”.

    1. I get Informed Delivery emails, but they don’t show everything (particularly junk mail), and they don’t indicate when the mail is actually delivered. I could see this being handy for knowing that the mail is actually in the box rather than wandering out to the box every so often.

  3. Oof! This is overkill in the extreme. It would be have been way easier to simply have a load cell at the bottom of the mailbox. An MCU waking up every few minutes to check the load cell and report back if it’s changed would do it. The power source could be a tiny amorphous solar cell would likely be able to power it during hours that mail is actually delivered.

    I’m not saying anything crazy like they should have just used 555 timers but… I mean, it’s possible. ;)

    1. A load cell can tell you *if* something is in the mailbox, but it won’t tell you **what** is in the mailbox. You won’t know if it is a bill or junk, or a small package or dead rat. OP’s camera will tell you that.

    2. It’ll also tell you how much the Robin sitting on the mailbox weighs, the amount of snowfall on the box, icicles, wind loading, etc. it’s not exactly “perfect” weighing the box to determine if your junk mail has arrived.

  4. A friend of mine did this once and got threatened with fines by the post office, it was technically violating a federal law that states only postmarked items are permitted inside mailboxes and only US postal employees are authorized to place them there.
    It appears to be totally at the post office inspector’s discretion what gets considered part of the interior of the box, what is considered an item inside the box and whether to press charges on this.
    I think the real problem was that the delivery person reported it because they had a (probably unjustified) belief that the surveillance device would be used to generate frivolous complaints against them which could harm their career or get them fired.

  5. For those in the US of A, you can sign up for email notices from USPS that will give you image scans of the mail you will receive that day. No email == no mail (or just junk inserts everyone gets).

    The last I knew they didn’t verify that the person receiving the email was the person who lived at the house, so it’s best to sign up anyway. There used to be (may still exist) a scam where someone would sign up to see what a person was receiving in the mail to look for credit cards, checks, etc.

  6. As others have said, the U.S. Postal Service will send you daily images for free via email of whatever they will be delivering that day. Our mailbox is a mile from our house and not near much else. Email easily gets here, but I’m pretty certain this IoT Mailbox doesn’t carry that far.

  7. a simpler solution (for my mailbox at least) would be a switch to detect if the flap has been lifted (no flap, no mail)
    then reset the status on keyed door opening.

    A load cell is probably overkill, and depending on the letter orientation may not trigger (eg if the letter leans awkwardly against the mailbox side)

    in the small, dark space a camera won’t be able to provide much info on what’s in the mailbox, and even if it could, would only give visibility of the nearest item.

  8. I would use one of those WiFi backscatter switches so I wouldn’t need batteries at the mailbox. Just a device underneath so opening the box hits the switch, informed delivery tells me for the most part what’s in there.

    Adding a bunch of electronics to your mailbox is one sure way to get it clobbered by a snowplow. Rule of law in this country may seem to be gone, but Murphy’s is still very strictly enforced.

    1. A hall-effect switch + a magnet would be what I’d do: the microcontroller can be in deep-sleep mode at all times with just a single pin reacting to the switch changing state, thereby consuming extremely little power over time. Also, yes, LoRa can easily handle that distance without a hitch.

      1. If you use a reed switch instead of a hall effect switch, you can put it between the battery and the processor. When the processor powers up, it can send a LoRa message. Closing the door would turn off the power again.

        If for some reason the processor needs to stay active longer than the minimal time to open and close the door, you can incorporate a relay to latch the power on until broken by the processor.

        A small window alarm sensor is an easy way to incorporate a reed switch and magnet.

  9. Congratulations on a cool project! Maybe you could do some ML on the images to differentiate receivers and types of post? I went with simplicity and it has been working for 4 years on the same 2xAAA batteries. Also, my mailbox is outside wifi-range. “No junkmail”-stickers are actually respected in my country, so I don’t have to worry about that. https://hackaday.com/2020/02/15/aaa-powered-lora-mailbox-sensor-goes-the-distance/

  10. Mine has been running great for almost 3 years now. It’s the one listed in the text (mailboxes that use proximity sensors). Here in Minnesota, Winters get to -30F. The key is the LiFePO4 battery, which is more stable than regular lithium batteries at lower temps. I’ve never had any issues with the battery. I have it wake up every 5 minutes to check the sensor. After 5pm it goes to deep sleep until 9am the next morning … that was key to keeping the battery alive at night. Two small solar panels charge it up during the day. It’s been running great and I get mail notifications for both “mail is here”, and “mail has been removed” every day. The notifications come to my smartphone via email (not text message). Sending an email from a website is free (text messaging is not). Email notifications and Text Message notifications look the same on an iphone so I’m only concerned that my phone beeps and displays message on home screen.

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