Prusa MK3 Spool Holder With Weight Scale (Side mount)

prusaprinters

<p>A side spool holder with an integrated scale.</p><p>Measure sort of exact the weight of the spool in grams using a load sensor connected to a HX711 24-bit ADC that an ESP866 samples every second. Weight is displayed on a 0.96" 80x160 RGB display (currently overkill as I only show a text in black…). There is a button for doing tare when there is no spool on the holder.</p><p>It works, but there are some things to improve:</p><ul><li>The load sensor is a rated for 50 kg which is unnecessary high and thus losing a bit of precision. Better to use a load cell rated for 2 kg.</li><li>Use two sensors instead of one to get a proper wheatstone bridge and increase the precision. Now one side of the bridge is replaced with two static resistors.</li><li>Due to only using one sensor and the lever effect, you have to always place the spool to the most left side of the holder to get a correct measurement. If the spool is moved to the right side the lever effect will cause weight to go up and show the wrong value.</li><li>There are some load cell creep over time that probably can be compensated for.</li><li>Auto turn off/on blacklight, use full potential of 65k RGB display, etc. But that is just code that needs to be added.</li></ul><p>The spool holder/adapter reuses the original prusa spool holder but only with one “handle”.<br/>Apart from the adapter, I also made a filament guide with support for a PTFE Teflon Tube. I found this working better (as in no scratch sounds, wear and tear etc) instead of having the filament running freely.<br/>For the adapter there a two separate plates on which the ESP (M2 screws)/HX711 board (hot glue) and the Display (M2 screws) / Button (hot glue) is mounted. This is to be able to iterate on the boards and also to make it easier to replace the display/esp with other hardware without the need of reprinting the whole adapter. The plates are mounted to the adapter using M3 screws. There is a through-hole for the display and button cable.<br/>I also had to print a stand that is screwed onto the load sensor to get a smaller contact area due to the slight angle of the adapter.</p><p>Included is a schematic on how everything is connected as well as all the code for the ESP8266/D1-mini for use in the Arduino IDE (make sure files currently named .txt ends with <i>.cpp</i> and <i>.h</i> respectively). I use <a href="https://github.com/ayushsharma82/ElegantOTA">ElegantOTA</a> for updating the code remotely as I rarely find the built in OTA to work. Use a 5V 500mA USB charger as power supply. In my case I power it from the Raspberry PI I use for octoprint.</p><p>I'm using <a href="https://www.home-assistant.io">https://www.home-assistant.io</a> for my home automation so I also hooked this scale into my Home Assistant as a light (the backlight for the display) and as a sensor (the weight sensor). Using this I can plot graphs of the weight over time as well as automatically turn off the backlight when going to bed/turning of the printer etc.</p><p>Credits to INeedOneDesigns for the original side spool holder which this is a remix of.</p><p> </p><h4>Part list</h4><ul><li>HX711 Load Cell Amplifier Breakout board: <a href="https://www.amazon.com/Amplifier-Breakout-Converter-Raspberry-Microcontroller/dp/B07MTYT95R">https://www.amazon.com/Amplifier-Breakout-Converter-Raspberry-Microcontroller/dp/B07MTYT95R</a></li><li>Geekcreit 0.96 Inch 7Pin HD Color IPS Screen TFT LCD Display SPI ST7735 Module: <a href="https://www.banggood.com/Geekcreit-0_96-Inch-7Pin-HD-Color-IPS-Screen-TFT-LCD-Display-SPI-ST7735-Module-p-1370911.html">https://www.banggood.com/Geekcreit-0_96-Inch-7Pin-HD-Color-IPS-Screen-TFT-LCD-Display-SPI-ST7735-Module-p-1370911.html</a></li><li>Geekcreit® D1 Mini V3.0.0 WIFI: <a href="https://www.banggood.com/Geekcreit-D1-Mini-V3_0_0-WIFI-Internet-Of-Things-Development-Board-Based-ESP8266-4MB-MicroPython-Nodemcu-p-1264245.html">https://www.banggood.com/Geekcreit-D1-Mini-V3_0_0-WIFI-Internet-Of-Things-Development-Board-Based-ESP8266-4MB-MicroPython-Nodemcu-p-1264245.html</a></li><li>50kg YZC-161B 50kg Half-bridge Load Cell Weighing Sensor: <a href="https://www.amazon.com/YZC-161B-Scale-Sensor-Half-bridge-Weighing/dp/B01MZ2AQ34">https://www.amazon.com/YZC-161B-Scale-Sensor-Half-bridge-Weighing/dp/B01MZ2AQ34</a></li><li>PTFE Teflon Tube with PC4-M6 Pneumatic Fitting and PC4-M10 Straight Quick in Fitting: <a href="https://www.amazon.com/Ewigkeit-Fitting-Straight-Pneumatic-Connector/dp/B07FS2Y148">https://www.amazon.com/Ewigkeit-Fitting-Straight-Pneumatic-Connector/dp/B07FS2Y148</a><br/> </li></ul>