How do you make Scales?

Hi, I am a year 12 design Technology student from Loreto Kirribilli. For my Major Design Project, I have to include two-scale components (max weight 2kg.) I have been browsing this site and understand I need a Strain Gauge Load Cell but am unsure how the use this product and further connect it to an LCD screen. If you would be able to assist me on how to do that/ what products I would need that would be amazing.Grace


The strain gauge is a resistance element - it presents a resistance that is based on the amount of bend that the load induces into the bar. So for your your project you would would fix one end to a base, and the other end to a plate. You would measure the resistance with no weight on the plate, and then measure again when the plate is loaded. A calculation will then tell you the weight. To measure the resistance, do the calculation and display the weight you would use a microcontroller of some type matched to a display - there is one example of measuring and displaying the resistance here but there are many possible variations on those components. The calculation would presumably be based on a calibration procedure to be done once the unit is assembled.


Hey Grace,

Welcome to the forum!

You’re on the right track with load cells. Digital weighing scales are built around either a 4-terminal load cell or four 3-terminal load cells.

For something like kitchen scales with a maximum load in the range of 100g to 10kg, similar to what you’re looking for, 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.

This 5kg Load Cell is likely going to be what you’re after. As mentioned on the product page for that one, pick the one that has at least 2x the max force/weight you intend to apply so you get the most precision with the right range. If you wanted to jump to a higher weight, you can also combine them. In the world of scales multiple load cells are simply parallel wired together. The combined output voltage is very, very accurate. This is the way nearly all multi-load cell scales work! Think the multiple points of contact on a bathroom scale.

You will also need to pick up a Load Cell Amplifier, the HX711 is a great pick from our store, and Sparkfun have put some great intel on their site to get them interfacing with an Arduino, you can find the info through the links on our product page.

From there the LCD should be easy, I’d grab something like this that’ll attach to the Arduino while still giving you easy access to the pins.