Solar eLabel

Write a text or send an image to a solar powered ePaper with your smart phone.

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This solar powered ePaper can be updated from any smart phone over Bluetooth Low Energy.

In 2017 the global market for sticky notes was 2,190 million US$. One small sticky notes block weights 40 g and costs EUR 2.69, about $3. This means in 2017 there was 29,000 metric tons of sticky notes produced (maybe less, because of discount if you buy bigger packs). A pine tree, which is used for making paper, can weight 3 tons. Without leafs, branches and bark, maybe half of it can be used for making paper. This means about 20,000 trees per year are used just for making sticky notes, which covers about 10 football fields. And this is just for the paper itself. Then you need energy to make it, the glue, the yellow paint etc. This product helps to reduce this.

The concept is easy:

- start an app on your mobile phone
- enter a text or draw an image
- press the button on the eLabel to transfer the text or image

The eLabel uses Bluetooth Low Energy, which means it needs no complicated pairing with the phone, and it doesn't need much power, so it can be powered from solar cells.

Some of the ideas of this project are based on my WiFi ePaper project. But WiFi needs too much power for solar cells, and with an additional server etc. it is too complicated for a consumer product. This eLabel product is much simpler to use and has many applications:

- replaces sticky notes
- label for conference room schedule
- public notes on a bulletin board
- price labels

It uses solar cells to power it, ePaper to display the content, which doesn't need power, and one button to update the display with a smart phone. Additionally the access can be restricted with a password, so that it can be used for price labels and other information that not everyone are allowed to change. Inside the device is a button to reset the password.

  • New parts

    Frank Buss05/28/2019 at 07:22 4 comments

    For a product later, the device shouldn't cost too much. So I searched for new ePapers, because the nice 4.2" Pervasive Display ePaper costs EUR 51. And I found the GDEW027C44 2.7" ePaper, also black/red/white, for about EUR 8. Still sufficient space for short messages, images or the coffee timer application.

    And for the solar cell I found this panel for EUR 2.89:

    Maybe not as efficient as the expensive ones you can get from Digikey, but the bigger size of 60x90mm should more than compensate it. It says 6 V / 0.6 W, but I guess only in bright sunlight at the equator, I will test it.

    It has 2 solder contacts on the back:

    There are many similar solar cell modules on eBay. If one module gets out of stock, I can just use one of the other modules. I think I can glue it to the case and use 2 holes to connect the cables, and it won't look too bad, because of the beveled edges.

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morgan wrote 04/18/2019 at 03:04 point

Look forward to seeing this come together. I would happily be the first in line to purchase, that coffee pot still needs a "Brewed X Hours Ago" sign.

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Frank Buss wrote 04/18/2019 at 06:58 point

It will have only Bluetooth, at least when powered with solar cells. But good idea, maybe I should add a RTC. It will be programmable with some kind of script, probably Lua, so a button press could display a custom text and the current time even without the hassle to use a smart phone to update the text.

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morgan wrote 04/18/2019 at 16:25 point

That would work for the minimal use case I'm interested in. What MCU did you switch to?

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Frank Buss wrote 04/18/2019 at 20:13 point

I'm thinking about using one of the Blue Geckos:

I have used this for a client project and it is a very nice low power chip, using only 2.5 µA in deep sleep mode with the built-in RTC running (with external 32.768 kHz crystal), and less than 10 mA when transmitting data over BLE.

The latest version for the ESP32 needs 30 mA:

This is already much better than before version 3, which needed more than 100 mA. And in deep sleep mode, with the RTC running, it needs 2.5 µA as well:

but it doesn't preserve the RAM content, as the sleep mode for the Blue Gecko does, so I think it is better to use this chip.

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