KUWTP Ep. 16 | 19th July 2024 | Constructing our weighing scale

Weight is just a number. Thankfully, we live in the day and age where information is readily available online – a huge saviour for the construction of our weighing scale. We meticulously followed the instructions of Indrek and spent an entire day in the lab soldering wires together to build our weighing scale.

Spoiler: We actually had to tear down and re-construct the weighing scale as the first construction possessed fatal electrical connection flaws that hindered our weight measurement and did not produce correct results when we tested the voltage diagonally across the board (which is supposed to be ~2000 ohms).

Some key learning points to note during the video is identifying the 3 different wires. Each load cell consists of 3 wires coming out of it, with either a positive or negative strain between each wire (Fig. 1). Correctly verifying the centre wire is crucial as it allows us to successfully get a resistance of 2000 ohms across the board when connected in a circuit (Fig. 2). The resistance between electrical components can be easily verified using a multimeter, to which one must be cautious when measuring and ensure the multimeter is in contact with the circuit only – otherwise the resistance obtained might be that of the human body (basically don’t use your hands to press against the test leads of the multimeter).

Another point where we strayed from the video are the connections between the HX711 module to arduino. The recommended connections are as follows:

• VCC to arduino 5V
• GND to arduino ground
• amplifier to arduino digital pin 4
• clock pin to arduino digital pin 5

However, this connection lead to us getting a NaN (not a number) reading on arduino. Upon switching the VDD to be connected to arduino 5V instead, it magically worked! #slay

Doing some research, VCC is the supply voltage of the circuit, and VDD is the working voltage of the chip: where C = circuit and D = device. Both are essentially power supply terminals.