ProCal: A Low-Cost and Programmable Calibration Tool for IoT Devices

TL;DR

ProCal is an affordable, programmable calibration tool for IoT devices that enhances measurement accuracy across sensors and power monitoring systems, using a scalable design controlled via software.

Contribution

ProCal introduces a low-cost, scalable, and programmable calibration platform utilizing digital potentiometers and resistor networks, with validated mathematical modeling and improved accuracy.

Findings

Reduces ADC error from 0.2% to 0.01% for ATMega2560

Costs less than 2% of commercial solutions

Provides extensive voltage and current calibration ranges

Abstract

Calibration is an important step towards building reliable IoT systems. For example, accurate sensor reading requires ADC calibration, and power monitoring chips must be calibrated before being used for measuring the energy consumption of IoT devices. In this paper, we present ProCal, a low-cost, accurate, and scalable power calibration tool. ProCal is a programmable platform which provides dynamic voltage and current output for calibration. The basic idea is to use a digital potentiometer connected to a parallel resistor network controlled through digital switches. The resistance and output frequency of ProCal is controlled by a software communicating with the board through the SPI interface. Our design provides a simple synchronization mechanism which prevents the need for accurate time synchronization. We present mathematical modeling and validation of the tool by incorporating the concept of Fibonacci sequence. Our extensive experimental studies show that this tool can significantly improve measurement accuracy. For example, for ATMega2560, the ADC error reduces from 0.2% to 0.01%. ProCal not only costs less than 2\% of the current commercial solutions, it is also highly accurate by being able to provide extensive range of current and voltage values.