Tuesday, 18 February 2014

Weighing scales project using a Load Cell and Custard Pi 3

This is an experimental project using a Load Cell and the Custard pi 3 to produce weighing scales. A circuit to amplify the signal and sample code is also presented.

The Load cell below (bought from E-Bay) was used.

The initital findings were:

1. This has a 4 wire interface. You need to supply a voltage on the red and black wires. I supplied 12V from a wall charger. The recommended range is from 10 to 15V.
2.  I attached a multimeter on the white and blue wires.
3.  Put a load of approximately 5 kG on the load cell
I got an output of around 5 mV on the white and blue wires.
The range of this load cell is from 0 to 5kg.
The input range on the Custard Pi 3 is from 0 to 2.5V. So to get the best accuracy from this load cell, we need an amplification of around 400 using an opamp.
After this you can feed the output of the opamp into one of the analogue inputs of the Custard Pi 3 (8 analogue input card) and calibrate the system.
The circuit diagram used is shown below.

Full description is provided on this page http://www.sf-innovations.co.uk/raspberry-pi-tutorials.html
Just click on the Custard Pi 3 weighing scales project.

Sample code is presented here  http://www.sf-innovations.co.uk/downloads.html
Just click on the sample code for wighing scales link.


This experimental project was to show how to use the Custard Pi 3 AtoD to interface to an external transducer, like a Load Cell. It’s up-to the reader to develop this further.


  1. Thanks for sharing!

    A load cell is a sensor or a transducer that converts a load or force acting on it into an electronic signal. This electronic signal can be a voltage change, current change or frequency change depending on the type of load cell and circuitry used. Looking for good load cell for you weighing machine, then purchase load cell at Alectronic and many other online manufacturers. Get load cells in a variety of configurations that are made from mild & stainless steel that are built to last and truck scale score boards & unmanned weighing systems too.

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