Self-calibrating universal input port

1. A circuit for sensing heating, ventilation, air conditioning, and refrigeration (HVACR) equipment, the circuit 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.

2. The circuit of claim 1 , wherein the microprocessor is further configured to:

set the first switch to the first open position;

set the second switch to the second closed position; and

determine a resistance of the DUT by calculating a third ratio of the second ratio and the first current.

3. The circuit of claim 1 , wherein the microprocessor is further configured to:

set the first switch to the first closed position;

set the second switch in to the second open position; and

determine a current of the DUT by calculating a third ratio of the second ratio and the load resistance.

4. The circuit of claim 1 , wherein the microprocessor is further configured to:

set the first switch to the first open position;

set the second switch to the second open position; and

determine a voltage of the DUT as the input voltage signal.

5. The circuit of claim 1 , wherein the microprocessor is further configured to periodically calculate the first ratio at a predetermined interval.

6. The circuit of claim 1 , wherein the amplifier comprises:

an operation amplifier having a first opamp input, a second opamp input and an opamp output;

a first resistor coupled between the first opamp input and the opamp output; and

a second resistor between the first opamp input and ground.

7. The circuit of claim 1 , wherein the input divider comprises:

a first resistive element coupled to the input port and the ADC and having a first resistance; and

a second resistive element coupled to the ADC and ground and having a second resistance.

8. The circuit of claim 7 , wherein the supply divider comprises:

a third resistive element coupled to the amplifier and the ADC and having a third resistance; and

a fourth resistive element coupled to the ADC and the ground and having a fourth resistance.

9. The circuit of claim 8 , wherein a third ratio of the first resistance and the second resistance is same or substantially similar to a fourth ratio of the third resistance and the fourth resistance.

10. The circuit of claim 1 , wherein the voltage-controlled current source comprises a first resistive element coupled to the amplifier and the second switch and having a first resistance.

11. 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.

12. The system of claim 11 , wherein the microprocessor is further configured to:

set the first switch to the first open position;

set the second switch to the second closed position; and

determine a resistance of the DUT by calculating a third ratio of the second ratio and the first current.

13. The system of claim 11 , wherein the microprocessor is further configured to:

set the first switch to the first closed position;

set the second switch in to the second open position; and

determine a current of the DUT by calculating a third ratio of the second ratio and the load resistance.

14. The system of claim 11 , wherein the microprocessor is further configured to:

set the first switch to the first open position;

set the second switch to the second open position; and

determine a voltage of the DUT as the input voltage signal.

15. The system of claim 11 , wherein the microprocessor is further configured to periodically calculate the first ratio at a predetermined interval.

16. 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.

17. The method of claim 16 , further comprising:

setting, by the microprocessor, the first switch to the first open position;

setting, by the microprocessor, the second switch to the second closed position; and

determining, by the microprocessor, the resistance of the DUT by calculating a third ratio of the second ratio and a first current of the voltage-controlled current source.

18. The method of claim 16 , further comprising:

setting, by the microprocessor, the first switch to the first closed position;

setting, by the microprocessor, the second switch to the second open position; and

determining, by the microprocessor, the current of the DUT by calculating a third ratio of the second ratio and a load resistance of the resistive load.

19. The method of claim 16 , further comprising:

setting, by the microprocessor, the first switch to the first open position;

setting, by the microprocessor, the second switch to the second open position; and

determining, by the microprocessor, the voltage of the DUT as the input voltage signal.

20. The method of claim 16 , further comprising periodically calculating, by the microprocessor, the first ratio at a predetermined interval.