Self-calibrating universal input port

A system for sensing heating, ventilation, air conditioning, and refrigeration (HVACR) equipment, the system comprising:

• a controller configured to control HVACR equipment;
• and
• an circuit coupled to the controller and comprising:
• an input port that, upon receiving a device-under-test (DUT), has an input voltage signal;
• a first switch coupled to the input port and a resistive load having a load resistance and having a first open position and a first closed position;
• an input divider coupled to the input port and dividing the input voltage signal;
• an analog-to-digital converter (ADC) coupled to the input divider, generating a first digital signal based on receiving an input voltage reference, 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;
• an amplifier coupled to the ADC and amplifying the output voltage reference to generate a supply voltage;
• a supply divider coupled to the amplifier and dividing the supply voltage to generate the input voltage reference;
• a voltage-controlled current source coupled to the amplifier and converting the supply voltage to a first current configured to drive the input port;
• a second switch coupled to the voltage-controlled current source and the input port and having a second open position and a second closed position;
• and
• a microprocessor coupled to the ADC and configured to:
• calculate a first ratio of the first digital signal and the supply voltage;
• and
• determine the input voltage signal by calculating a second ratio of the second digital signal and the first ratio.

A method for sensing heating, ventilation, air conditioning, and refrigeration (HVACR) equipment, the method comprising:

• receiving, by a microprocessor, a first digital signal converted from a first voltage-divided representation of a supply voltage;
• calculating, by the microprocessor, a first ratio of the first digital signal and the supply voltage;
• receiving, by the microprocessor, a second digital signal converted from a second voltage-divided representation of an input voltage signal corresponding to a device-under-test (DUT) coupled to an input port;
• determining, by the microprocessor, the input voltage signal by calculating a second ratio of the second digital signal and the first ratio;
• setting, by the microprocessor, a first switch coupled to the input port and a resistive load to a first open position or a first closed position;
• setting, by the microprocessor, a second switch coupled to the input port and a voltage-controlled current source to a second open position or a second closed position;
• and
• determining, by the microprocessor, a resistance, a voltage, or a current of the DUT based on the first switch and the second switch.