Week 6: The Final Countdown

I wanted to refine my code removing all debugging and extract my calculations and MQTT subscriptions. This would make the code flow a little easier and easier to follow should anyone view my HX711 implementation and approach to designing my code.

I have been using a private GITHub to save a repository of my code. To view my code I have compressed my project files to a password protected zip file here. The password is in the file submission in UTS turn it in, otherwise contact me here and I can run you through it.

I was offered an opportunity to head down to UTS Protospace to see the progress of my prototype model with Peter McClean and Danon Bradford. We managed to get into Protospace and see what the department is capable of. There are large scale 3D prints on an almost 1 m2 printer. Some of these prints included furniture designs and a model of the Eiffel Tower. I also found some prints that would be close to what my model would turn out like.

With my sketch model available I wanted to get ahead and calibrate the single strain gauge so I could work further on developing my software features. I decided I would try rewiring my technical package to accommodate for 2 strain gauges providing more stability for weighing a bottle for my test cases. I then reverted back to a single bar gauge and 4 gauges to see whether I could achieve a solid test case to properly explore further development.

I was unable to do any further development which involved practical testing of the strain gauge until my prototype model arrived so I wired my components back to a single 50kg strain gauge. The serial output started only showing zero readings which made me very nervous on the final day of development.

My prototype model had arrived, click here for more details, so I began soldering my Node MCU D1 Mini, HX711, charge module chip, 2 x 1000 KOhm resistors and single 50kg strain gauge. My new chip fit into my model after I screwed it together and I now needed to upload my code into it to begin testing. I got zero readings. 

I continued to debug my issue through software looking back to previous models and found no relief. I then looked at hardware resoldering my D1 Mini circuit a couple of times to no avail. I switched back to my bread board to debug using my ESP8266 chip to find a solution.

I finally rewired my resistors and strain gauge on the breadboard to get a solid connection and my reading came back. I looked at my D1 Mini realising the screwing motion broke the solder on the resistors and interfered with the Serial USB connector on the d1 Mini. My problems were mechanical. The wires of the strain gauge were so small and fragile it was becoming impossible for me to solder them correctly given the time I had. 

I decided I would stick with my breadboard circuitry for the showcase to prove my case with further time required to resolve my soldering issues.

My prototype model had arrived, I am very pleased with the outcome. All the threads work well although my bottom thread needed just a little sanding back the result was perfect.

My technical components fit in especially the HX711 chip that slides under the strain gauge. The tolerances were 0.5 mm for the prototype overall which was enough to allow all separated and moving parts to fit together with ease.

The weight plate balanced well under the anterior lip of the outer housing and on top of the single strain gauge. This will allow me at this late stage to test and calibrate my gauge properly as stability calibrating the strain gauge in a “real world” scenario was without the prototype model. My sketch model would have required too much time in sanding and preparing to make the bottle and weighing plate fit in the outer collar for testing teh strain gauge.

Without calibration, now the strain gauge is working, I can show my proof of concept for our showcase with possible further work in the future to refine and realise this product’s potential.