Isolated Potentiometer and Switch Module using LOC110

This is an Isolated Potentiometer Module that integrates a LOC110 linear optocoupler, an isolated DC-DC converter, an onboard 10K linear potentiometer, 2 x tactile switches, 2 x PC817 optocouplers, and supporting circuitry. It is designed for reliable use in VFD drives, process control, PLCs, automation systems, and other industrial applications where isolated analog signals and isolated switch inputs are required.

The two tactile switches are connected through two PC817 optocouplers, ensuring isolated operation. By default, outputs C1 and C2 remain high, and transition low when a switch is pressed.

Thanks to the onboard isolated DC-DC converter, the module operates from a single 5V DC supply, simplifying system integration. With the full rotation of the potentiometer, the output provides a 0–3.3V DC isolated analog signal, fully isolated from the potentiometer input.

At the core of the design is the LOC110 linear optocoupler, which provides 3750V isolation. The MCP6001 op-amp (U2) functions as a closed-loop servomechanism, sensing the photodiode current and driving the optocoupler’s LED to maintain accurate linearity. A second MCP6001 (U3) further conditions the phototransistor output. An onboard power LED (D1) indicates the active input-side supply.

The LOC110 incorporates an infrared LED optically coupled to two photodiodes. The feedback photodiode stabilizes the LED current, compensating for nonlinearity, time drift, and temperature variations, while the output photodiode delivers a highly linear, isolated analog signal.

This architecture ensures wide bandwidth, robust input-to-output isolation, and excellent servo linearity.

Features

• Single 5V DC supply operation
• Onboard 10K linear Potentiometer
• On Board 2 Tactile Switch
• Integrated isolated DC-DC converter
• Power status LED indicator
• 0–3.3V DC isolated output
• PCB Dimensions: 47.15 × 35.08 mm
• 4 x 3mm PCB Mounting Holes

Connections

• CN2: Pin 1 = 5V DC Input, Pin 2 = Analog Voltage Output 0 to 3.3V DC, Pin 3 = GND
• CN3: Pin 1 = Collector 1 with Pullup Normally High, Pin 2 – Emitter Connected to GND, Pin 3 = Collector 2 with Pullup Normally High, Pin 4 – Emitter Connected to GND
• R15: Potentiometer
• D1: Power LED Input Side
• SW1= Switch 1, Output Collector-1 (CN2 Pin2/C1) goes low when this switch is pressed (Normally High)
• SW1= Switch 2, Output Collector-2 (CN2 Pin3/C2) goes low when this switch is pressed (Normally High)