e-Gizmo 50A (125A peak) AC/DC Current Sensor Board HLSR 50-P with TRIMPOT

Theory of Operation

This compact module is designed for precise, isolated AC, DC, or pulsed current measurement. Below is a breakdown of how the circuit and its primary component, the LEM HLSR 50-P, operate.

1. Core Sensor Technology (U1)
At the heart of the module is U1, the LEM HLSR 50-P current transducer.
-Hall-Effect Transduction: It operates on the open-loop Hall-effect principle. When current passes through the primary circuit via the terminal block (J2), it flows through internal bus bars connected to pins IN1+/IN2+ and IN1-/IN2-.
-Magnetic Coupling: This current generates a magnetic field proportional to its magnitude. A high-bandwidth, low-loss magnetic core inside the IC concentrates this field onto an internal Hall-effect plate.
- Galvanic Isolation: Because the primary current only couples magnetically to the internal sensor, there is complete physical and electrical (galvanic) separation between the high-power input path (J2) and the low-voltage control electronics (J1).

2. Signal Generation & Referencing
- Ratiometric Voltage Output (Uout): The transducer outputs an analog voltage on pin 2 (Uout) that tracks the measured primary current.
- Reference Voltage (Uref): Under zero-current conditions, the sensor outputs a stable reference voltage at pin 1 (Uref), which typically sits at half the supply voltage (e.g., 2.5 V when powered by a +5 V rail). As current flows in a positive or negative direction, Uout swings linearly above or below this Uref level
-.Filtering: Capacitors C1, C2, and C3 (100 nF) act as decoupling and bypass elements for the sensitive Uout and Uref lines to suppress high-frequency noise.

3. Scale Calibration & Readout Interface (RV1 & JP1)
The module features a highly versatile scaling network at its output stage:
-The Scaling Network: A 100 kOhm multi-turn trimpot (RV1) is connected directly between the output (Uout) and the reference (Uref).
- Adjustable Output vs. Direct Pass-Through:
-- When JP1 is open (not shorted): The output signal fed to the header pin OUT (J1, pin 3) is tapped from the wiper of RV1. This allows you to scale the sensor's raw sensitivity (e.g., matching a default 16 mV/A down to 10 mV/A). This calibrated output is ideal when reading the signal directly with a Digital Multimeter (DMM), as it translates directly to round-number scale factors.
-- When JP1 is shorted: The trimpot RV1 is bypassed, routing the raw, unattenuated output (Uout) directly to the OUT terminal of header J1.
-Filter Capacitor (C4): A 33uF capacitor (C4) stabilizes the output, filtering ripple and low-frequency noise for cleaner micro-controller or multimeter ADC reads.

4. Power Supply & Indication
Power Input: The module operates on a single +5 V supply fed through pins 1 (+5V) and 2 (GND) of header J1.

5. Schematic Diagram