Xiaomi Mijia Clock\Temp Rechargeable Mod

prusaprinters

<figure class="table"><table><tbody><tr><td style="background-color:#000000;">&nbsp;</td></tr><tr><td style="background-color:#f9cd42;"><p>A warning first: This project involves using lithium ion pouch cells, which is one of the most dangerous types of batteries available. They are easy to physically damage with anything sharp or pointy. If the bag is pierced it will most likely catch fire. After years of use they may also expand due to gas building up - which is normal, but if it starts pressing against something sharp, it can burst into flames.</p><p>Also; I can't guarantee these things will work at this voltage long term. I've tested them up to 5 volts for a few days, which seems fine, but I'm not sure if all components can take the higher voltage continuously. Should be fine since components tend to blow up instantly if the voltage is too high. Still, make this at your own risk.</p><ul><li>My devices has been running for over 2 months now, so the higher voltage seems fine.</li></ul></td></tr><tr><td style="background-color:#000000;">&nbsp;</td></tr></tbody></table></figure><p><strong>---------------------------------------------------------------------------------------------------------</strong></p><p>The Xiaomi Mijia E-INK series of products look pretty nice but they seem to use the coin cell batteries pretty fast compared to regular LCD types (especially the clock). This mod removes the need to keep buying those batteries.&nbsp;</p><p>The mod is simply an extended back cover that allows for more space inside for bigger batteries and a USB charger board. A typical 3v 2032 coin cell has a capacity of about 200mah. If replaced with a 4.2v 500mah lithium, the capacity will increase around 3.5 times for the temp\hygrometer. Can also be powered forever with just USB and no battery.</p><p>Prints solid. No supports.</p><ul><li>These back covers replaces the original ones but uses the same screws.</li><li>PLA should be fine.</li><li>The units can stand on their own but there is a wall mount for both available as well, which can be screwed or attached with 10mm wide double-sided tape. There is also a reverse mount for the hygrometer that's for mounting it on the inside of glass (also fits stock model).</li><li>The hygrometer has an extender for the button that switches between C\F. You will need the original rubber insert though.</li><li>The low battery warning may not work because it shows at 2.5v, which is the same voltage that the protection chip(s) disconnects the battery.</li><li>For the hygrometer, the main chip and SHT30 sensor can take up to 5.5v. More unsure about the clock chips.</li><li>The charger board will output some heat when charging that will affect the temperature reading for a while.</li><li>The charging current for the TP4056 boards defaults to 1A. This might be a little high for smaller batteries so it's recommended to change the resistor that decides what the current is. I changed the one for the 500mah battery to 2K, which cuts down the current to around 500ma. You can see where it is in the picture.</li><li><strong>The positive connector inside the units is very sharp.</strong> It should be removed so it doesn't cut the new battery. Anything sharp should be covered or removed. Check for pointy solder blobs too.</li><li>Battery should be taped down so it doesn't bounce around inside, ideally in the bottom for better balance.</li><li>Batteries in the clock are in parallel so it doesn't matter which connector you use.</li><li>The clock has a small secondary battery for keeping settings. This is not connected to the other battery terminals so it wont be attempted charged.</li><li>TP4056 is glued in place. They can reach 50°C during charge, so maybe not hotglue.</li></ul><p><strong>---------------------------------------------------------------------------------------------------------</strong></p><h3>Parts needed:</h3><ul><li>Wires</li><li>Original screws</li></ul><figure class="table"><table><tbody><tr><td style="background-color:#40C8E818;width:350px;"><p><strong>TP4056 USB Charger</strong></p><p>These are USB battery chargers that works on pretty much all common single cell lithium batteries. Available with micro-usb or usb-c (not sure if the usb-c will fit though).</p><p>Also available with or without battery protection chips (the longer one, which I use).</p><p>Easy to find all over the place, like eBay.</p></td><td><figure class="image image-style-align-center"><img src="https://media.printables.com/media/prints/218583/rich_content/b90f01a4-f0fa-42b6-ab08-d3678e69880c/x1.png#%7B%22uuid%22%3A%2220838d4a-5cd7-4352-8c56-a7f43d7d37b9%22%2C%22w%22%3A1600%2C%22h%22%3A1200%7D"></figure></td></tr><tr><td style="background-color:#40C8E818;width:350px;"><p><strong>Lithium Battery</strong></p><p>These are lithium pouch cell batteries. The numbers on them are the dimensions of the battery. May come with or without a protection board. If it does not, you HAVE to use the protected charger board (double protection is fine).</p><p>I get these from eBay seller “<a href="https://www.ebay.com/sch/tesky12/m.html?_nkw=&amp;_armrs=1&amp;_ipg=&amp;_from=">tesky12</a>”. You can buy sets of these to get more for your money.</p><p>I use the 503450 and 502540, which are 1000 and 500mah. I wouldn't use thicker batteries than 6mm. These are 5.&nbsp;</p></td><td><figure class="image image-style-align-center"><img src="https://media.printables.com/media/prints/218583/rich_content/e56fa051-6efb-48fa-9fa0-f4a16c63c10b/x2.png#%7B%22uuid%22%3A%22c9441b98-2171-4fa2-8893-1fc6ebf263c1%22%2C%22w%22%3A1600%2C%22h%22%3A1200%7D"></figure></td></tr></tbody></table></figure><p><strong>---------------------------------------------------------------------------------------------------------</strong></p>