At the in London we hold repair events where members of the public are invited to bring in all manner of electrical and electronic items for repair, so as to save them from landfill. A few months ago (at an event I didn't actually attend) someone brought in some faulty kitchen weighing scales which nobody could fix. Never having seen inside any digital weighing scales and not knowing how they work, I took it as a challenge to research them, in the process, building two versions of my own. If you wish to build your own weighing scales or incorporate a weighing function in a wider project, you can use this Instructable as a basis, whatever your requirements, from weighing fractions of a gram up to many kilograms. Hence I will concentrate on the electronics, the software and the underlying principles. How you realise your own project is completely up to you.
I will also show you how to calibrate them, even if you don't have any standard weights. Having done my research and having validated it by building my own scales, I wrote up the principles of weighing scales, including whatever I could deduce about fault-finding, in the Restart Project. Go and take a look! All digital weighing scales are built around either a 4-terminal load cell or four 3-terminal load cells.
Which to get depends on what sort of scales you want to make. They are all electrically compatible and fairly cheap so you can change your mind later, or get more than one type to experiment with. For kitchen or postal scales with a maximum load in the range of 100g to 10kg, you can get 4-terminal load cells consisting of an aluminium bar. This is mounted horizontally, supported at one end and supporting the weighing platform at the other. It has 4 strain gauges attached to it.
![Arduino hx711 weight scale interface 1 0 software free Arduino hx711 weight scale interface 1 0 software free](https://images-na.ssl-images-amazon.com/images/I/418MiJzTM%2BL._SX342_.jpg)
I explain fully how it works in my article so I shan't repeat it here. These are less suitable for heavier loads such as bathroom scales, where a person's full weight, not necessarily centred on the platform, is better supported by 4 load cells supporting the 4 corners of the platform. This is where four 3 terminal load cells are more suitable.
![Interface Interface](https://images-na.ssl-images-amazon.com/images/I/61XKXMfhd6L._SX425_.jpg)
The HX711 module based on HX711 consist of an amplifier and a precision 24-bit analog-to-digital convertor (ADC) designed for weigh scale applications to interface directly with a bridge sensor. HX711 module operates at 5V and the communication is executed through a serial (clock-data) interface. For connecting load cell to arduino, you need prepare an amplifier module such as HX711 and connect all wire same to below link. After, you download example library for HX711 and test your load cell.
Ones rated at 50kg each are widely available, which together will weigh up to 200kg. Others with even higher ratings are designed for suspending the weight to be measured after the fashion of luggage scales. In addition to your load cell or load cells, you will need: • An Arduino. You can use virtually any type you like but I used the Nano as it has the USB interface built-in and still only costs a few pounds. • A HX711 module.
This may come bundled with your load cell but is available very cheaply as a separate item from many sources. • For prototyping, a 400 point breadboard, jumper leads, pin and socket strips. You will also need wood, plastic, screws, glue, or whatever you require for your particular version of the project. To use the HX711 module on the breadboard, solder a 4-wide pinstrip to the interface pins (GND, DT, SCK, VCC) of the HX711.
For easy connection and disconnection of the load cell (particularly if you're experimenting with more than one sort) solder a 6-wide pin socket strip to the analogue pins. (You only need the E+, E-, A- and A+ pins but I fitted a 6-wide strip anyway in case I wanted to experiment with the other two.) If you are using a 4-wire load cell you will then need to solder the 4 leads from the load cell to a 4-wide pin strip. The first two pins will be E+ and E- and the other two A- and A+.