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+--- Thread: KC868-A16 – Using AI3/AI4 (0–5V) as 4–20mA Inputs Without Replacing SMD Resistors (/showthread.php?tid=9831)
KC868-A16 – Using AI3/AI4 (0–5V) as 4–20mA Inputs Without Replacing SMD Resistors - ramiavdiel - 09-14-2026
Hi KinCony,
We are using the KC868-A16 and need four 4–20mA inputs.
AI1 and AI2 are already configured for 4–20mA, while AI3 and AI4 are configured for 0–5V.
We understand from the schematic that converting AI3/AI4 internally would normally require replacing the SMD resistors (5.1kΩ / 10kΩ network with the 0Ω / 150Ω configuration used on AI1/AI2).
We would prefer not to modify or solder components on the PCB.
We tested an external solution on AI3 by connecting a 220Ω resistor externally across the analog input and GND.
With a 4–20mA pH output connected, the controller showed pH 2.41, and we measured approximately 1.460V at the AI3 input. After taking the existing internal resistor network into account and applying the appropriate conversion in our ESP32 firmware, we were able to obtain almost the same pH value.
The measurement also appears electrically stable at the input.
Our question: Is using an external resistor in this way a safe and recommended solution for continuously using AI3 and AI4 as 4–20mA inputs?
Is there any disadvantage or protection/accuracy issue compared with changing the onboard resistors?
If you recommend a different external solution that does not require PCB soldering, please let us know.
Thank you.
RE: KC868-A16 – Using AI3/AI4 (0–5V) as 4–20mA Inputs Without Replacing SMD Resistors - admin - 09-14-2026
You can connect a 150-ohm resistor in parallel at the analog input port to convert the current signal into a voltage signal.