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Arduino Load Cell

MICRO-LOAD CELL

Here is the micro-load cell I used.  The strain gauges are bonded to the metal.

LOAD CELL SUPPORT

I have fixed the load cell onto a wooden box with metal fixings to stop the wood from crushing.

LOAD CELL SUPPORT

The wooden box is simple some lengths of baton joined with dowels.

A load cell measures weight using strain gauges

Measuring forces is an important aspect of engineering.  We can use a load cell to measure force.  The force we are going to measure in this example is the weight of an object.  Load cells can be found in your electronic kitchen scales and we are essential going to make a set of scales.  The advantage of making a set of scales from scratch is that they are then easy to connect to other devices and/or record the data for other uses etc.

Firstly credit where credit is due, I’d like to thank Christian Liljedahl.  His web site (Link Here) was a great help in pulling this project together.
There are a number of different designs of load cell. In this project I am using a 3133 micro load cell as shown in the photo.  Each load cell has a rated capacity.  The one I’m using has range of 0 to 5 kg.  The load cell is a metal bar with strain gauges glued to it.  When a load is placed on the bar it deforms very slightly due to the shear force.  This deformation is measured by the strain gauges.  We will measure the output voltage of the strain gauge as the voltage changes more the more the bar deforms. The change in voltage is very small, however.  We will amplify the output using the INA 125P.  

The first step is to build a support for the load cell.  For the unit I am using the end with the wires should be secured and the load applied to the other end.  I quickly made a wooden frame to hold the load cell.  I have placed metal fittings around the load cell as I was concerned that the wood would crush under load.  I have also made a small wooden platform to carry the objects we want to weigh and secured this to the other end.  

What is a Load Cell?


Next Step

SIDE NOTE


A load is the force of the mass of an object due to the acceleration due to gravity.  This is normally called the weight of an object.  It is different from the mass of an object.  The mass is the density multiplied by the volume.  The mass and weight are related by gravity (Force (load) = Mass x Acceleration Newton’s 2nd Law).  That is why you will weigh differently on the moon.  Your mass hasn’t changed but gravity has.  The unit of mass is the pound or kilogram and we often talk of things having a weight of 5kg.  Strictly speaking this is its mass.  The weight of the object measured in Newtons (the unit of force) is 5 x 9.81 (the acceleration due to gravity in m/s2) = 49N.


© Flow RC June 2014

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