Propane Weigh Scale Hack

Have been using my propane weight scale hack for over a year and it is awesome!  Life caught up to me and I didn't get to finish my hack logs, but I will have more time now to make more entries about the software in the last few weeks of December....so stay tuned.!  In the mean time...here's a shot of one of the iPhone screens that I designed using RemoteXY application....it's amazing...!

Now that I had the Wheatstone thought out, I connected it to the HX711 and wired it as per the example schematic.  I had to add the two fixed 1000 ohm resistors per the diagram to make the Wheatstone a full four cell bridge.   I added in the color codes of the load cells to the sketch and it is wired internal just like this really Ugly hand sketch shows.  Having found the HX711, I went looking for an ESP32 type chipset that was the smallest unit that I could find that was in stock and available.  I stumbled into the TinyPico.....it is a full ESP32 with WiFi and BLE and extremely small.  I will take more pictures of the installation in future log entries.  But I was able to wire it up and tested it and it worked with the example sketches...!!   A lot of software work needed to be done....and I was still on the lookout for a way to communicate with an iPhone.   The hunt for that continued......

The TinyPico ESP32 Super Small Chipset

Having drawn out the main PCB portion....I measured the load cells and did another Ugly Sketch of just the Strain Gauges and how they configured into a wheatstone bridge.   Knowing this would allow me to add my own load cell amplifier to this circuit and then output to an AVR type microprocessor.   Since I didn't need to recreate the wheel here....I ended up using the HX711, which already had libraries that were well documented and were usable in ESP32 type chips.....which I wanted to use because of their WiFI and Bluetooth capabilities.  Wiring diagrams are on the SparkFun page....but I will do a full diagram when I am done with the project.

Sparkfun HX711 Load Cell Amplifier

I started off this project by trying to understand how the existing scale platform was electronically connected.   So I just started drawing a sketch based on iphone pictures that I took of the PCB and load cell wiring.  It was an UGLY view into basically a 3 way Strain gauge wired as a WheatStone bridge of sorts.  The big ah-ha moment was that there were few 3 strain gauge load cell wiring diagrams on the internet......but after deciphering their PCB, I noticed that they filled in the fourth strain gauge with just passive resistors that were trimmed to equal the series resistance of the other 3 strain gauges.  So I had a VERY UGLY but preliminary sketch and that was a good start!