Testing the Load Cell

Original Amplifier Shield Setup

After ordering a proper amplifier shield to boost the small voltage changes that Wheatstone bridge on the load cell gives off, some Arduino programming was done to interpret the voltage as load. Fortunately, the amplifier shield purchased was configured to output a boosted voltage that the built in Analog to Digital Converter could read and convert to integer values (0-1023 for a 10 bit system). However, this was found to be inadequate for the load cell and could only give an accuracy of 1.54 LBS per integer value. In other words, a 5V input divided up into 1024 sections yields a readable voltage change of 4.9mV (5V/1024=0.0049V). The load cell is capable of reading changes much smaller than 4.9mV so some changes were in order because the system needed to be more accurate than 1.54 LBS for measuring the rocket engine thrust.

Amplifier Shield coupled with the 16 bit ADC

So, to make this more accurate, a 16 bit Analog to Digital Converter was used. The ADS1115 board, made by Adafruit, was the perfect solution for this problem. The 16 bit resolution yields 32,768 individual integer values, far greater than 1024. So 5V/32,768 = 0.000152V or 0.152mV. This is 32x better than the Arduino's on-board analog to digital converter. Furthermore, since the output from the 16-bit ADC is no longer analog and now digital, the Arduino's ADC can be bypassed and the digital output can be read with just any ordinary pin on the Uno board. This made taking measurements astronomically easier and like said, 32x more accurate.