Development and Testing of a System for Automated Resistance-Voltage Characterization of Programable Optically Variable Resistors

An automated system for resistance-voltage (R-V) characterization of programmable optically variable resistors (POVRs) has been developed. It integrates an ESP-32 microcontroller to modulate the forward bias voltage across the POVR’s light emitting diode (LED) sources via pulse-width-modulated (PWM) signals and measure the corresponding resistance of the light-dependent resistor (LDR)-detector. The forward bias voltages are incrementally varied from zero to the LEDs’ rated values. To accommodate the LDR’s resistance range (from a few megaohms to hundreds of ohms), a 1×6 multiplexer circuit with six precision resistors (10 MΩ to 100 Ω, ±1% tolerance) and corresponding transistor switches ensures automatic range selection. The R-V characteristics of POVRs with four spacer lengths were measured both manually and with the automated system. The automated system demonstrated high accuracy, with a mean percentage error below 2.5%, showcasing its reliability and efficiency for POVR characterization.