An illustrative embodiment disclosed herein is a circuit for sensing heating, ventilation, air conditioning, and refrigeration (HVACR) equipment. The circuit includes an input port that has an input voltage signal. The circuit includes an analog-to-digital converter (ADC) generating a first digital signal based on receiving a representation of a supply voltage, generating a second digital signal based on receiving the divided input voltage signal, and outputting the first digital signal, the second digital signal, and an output voltage reference. The circuit includes an amplifier coupled to the ADC and amplifying the output voltage reference to generate a supply voltage. The circuit includes a microprocessor coupled to the ADC and configured to calculate a first ratio of the first digital signal and the supply voltage. The microprocessor is configured to determine the input voltage signal by calculating a second ratio of the second digital signal and the first ratio.