4.1 Configuration 1: Single Conversion without PGA Usage

In the first configuration, the ADC operates in Single Conversion mode with the PGA disabled. An object weighing 2.003 kg is placed on the scale, and 300 ADC samples are recorded and analyzed.

As observed in the above chart, the input signal is not usable without prior conditioning. According to the load cell's data sheet its capacity and output are rated at 5 kg and 1.0+0.15 mV/V, respectively. The load cell outputs 3.3 mV at maximum capacity when supplied by 3.3V. Performing ADC conversions on signals of this scale without prior amplification proves unsuitable as the LSB voltage is in the range of 0.5 mV when the ADC is operating in differential mode, and the voltage reference is 1.024V. In this case, as the resolution is inappropriate, minor variations of the ADC output translate into considerable changes in the computed weight. It is, therefore, impossible to detect any minor input signal variations. Taking into account these observations, the internal PGA proves instrumental in the development of the weight scale application featured in this document.