Load Cell Weight Measurement

This user guide looks at the steps needed in order to set up a weight measuring system using a load cell. Weight is converted into voltage which in turn is rescaled using code in the Arduino which converts digital units back into weight which corresponds to the weight inputted on the load cell.

Components Needed:

Load Cell

Arduino Nano

INA122 Instrumentation Amplifier

Bread Board

Resistor(s)

Load cells are sensors that detect force. When force is applied to a load cell, it converts the force into an electrical signal. Load cells are also known as "load transducers," because they convert a load into electrical signals. For example, when a certain weight is placed on the load cell, the force of this weight will be converted into voltage corresponding to the weight applied.

The INA122 is a precision instrumentation amplifier for accurate, low noise differential signal acquisition. In simple terms, this particular type of amplifier is well suited to turning low input voltage levels into higher voltage levels. A single exterior resistor can be added to set the 'gain' of the amplifier. This allows the user to dictate the output voltage produced by the amplifier.

The images seen above indicate the pin layout of the instrumentation amplifier.

The Arduino Nano is Arduino's classic breadboard friendly designed board with the smallest dimensions. The Arduino Nano comes with pin headers that allow for an easy attachment onto a breadboard and features a Mini-B USB connector.

The Arduino will be used to code and implement the rescaling part of the process.

This code is uploaded to the Arduino to scale the voltage into digital units and to output the Mass value.

In building the circuit we will first start by placing the LNA122 op amp onto the breadboard positioned in the middle preferably, now from looking at the LNA122 specifications in the above section we can locate Pin 3 and connect the Green wire of the Loadcell to pin 3, Next locate pin 2 and connect the White wire of the Loadcell to pin 2.

The remaining two wire of the loadcell are used to power the device. In order to do this an ac power supply of 12 volts must be connected to the Breadbord, this can be done by connecting the positive terminal of the power supply to the positive terminal row on the Breadbord and the Negative terminal of the power supply to the Negative terminal row of the Breadbord. Now all that needs to be done is connect the Red wire of loadcell to the Positive row of the Breadbord and connect the Black wire of the loadcell to the Negative row of the Breadbord.

Connecting the resistors to the operational amplifier to determine the gain of the op amp can be done by connecting the 520 ohm resistor in series from pin 8 to pin 1. Next the operation amplifier needs to powered this is done by taking a second 12v power supply and connecting the positive terminal to the pin 7 of the operation amplifier and the negative terminal to pin 4 of the operation amplifier, Vref is located at pin 5 and must be connected to the ground of the 12v supply.

The Arduino Nano can now be placed on the Breadbord. Now that all of the input wires are connected to the operation amplifier the output located at pin 6 must now be connected to pin A7 of the Arduino Nano. The Arduino can now be powered by a 5v power supply, the Positive terminal should be connected to the 5V pin on the Arduino and the negative terminal should be connected to the ground pin (GND).

Now that everything is connected Code can then be uploaded onto the ardiuno nano, Once this is complete power can now be supplied to all the componence mentioned above and the circuit will be functional and readings for weight can be seen in the serial monitor tool in the Arduino program.