SM351LT Magnetoresistive Sensor Breakout Board
Overview
The Boardoza SM351LT is an ultra-sensitive, nanopower magnetic sensing solution designed to replace traditional reed switches and standard Hall-effect devices in battery-constrained applications. Built around the Honeywell SM351LT magnetoresistive (MR) sensor engine, this module offers omnipolar detection capabilities, allowing it to trigger in the presence of either a North or South magnetic pole with equal precision.
Unlike diverse Hall-effect sensors that require significant operating current, the SM351LT utilizes a state-of-the-art magnetoresistive bridge architecture. This enables it to achieve reliable switching at typical currents as low as 360 nA (nanoamperes), making it the gold standard for "install-and-forget" battery-operated systems like utility meters, medical infusion pumps, and wireless security contacts.
Core Technical Specifications
The module is defined by the following operational parameters:
Sensing Technology: Omnipolar Magnetoresistive (MR) sensor, offering superior sensitivity compared to standard Hall devices.
Operating Voltage: Extremely wide input range of 1.65V to 5.5V DC, accommodating direct connection to 1.8V logic, coin cells, or 5V buses.
Supply Current: Ultra-low power consumption, typically averaging 360 nA at 2V, enabling multi-year battery life.
Sensitivity: High-sensitivity switching point (typical operating point around 14 Gauss / 1.4 mT), allowing for the use of smaller, cheaper magnets or larger air gaps.
Output Configuration: Push-Pull (CMOS) output stage. This eliminates the need for an external pull-up resistor, saving component count and board space.
Operating Frequency: Capable of detecting magnetic field changes up to 1 kHz, suitable for low-speed counting applications.
Thermal Endurance: Rated for industrial temperature ranges from -40°C to +85°C.
Physical Dimensions: A compact 20 mm x 40 mm PCB footprint.
Key Engineering Features
Omnipolar Detection Logic
The module is "pole independent," meaning it activates (switches output state) when the magnetic field magnitude exceeds the operating point (), regardless of whether the field is North or South polarity. This drastically simplifies manufacturing assembly and installation, as magnet orientation does not need to be strictly controlled.
Nanopower Architecture
The defining feature of the SM351LT is its duty-cycled power management. The internal logic wakes up the sensing element for a brief interval to sample the magnetic field and then returns to a deep sleep state. This periodic sampling occurs fast enough to appear continuous for most human-interface and mechanical monitoring applications while maintaining sub-microampere average current.
Robust Solid-State Design
As a solid-state device, the Boardoza SM351LT suffers from none of the mechanical wear, contact bounce, or "sticking" issues associated with glass-encapsulated reed switches. It is immune to vibration and shock, providing high reliability in mobile or industrial environments.
Hardware Interface and Signal Mapping
The module simplifies integration via a standard 3-pin interface:
Power and Signal
VCC: Power Supply Input (1.65V - 5.5V).
GND: Common System Ground.
OUT: Digital Output Signal.
State Low (0V): Magnetic field detected (Field > Operating Point).
State High (VCC): No magnetic field detected (Field < Release Point).
(Note: As a push-pull output, this pin drives the logic line actively high and low; do not use strong external pull-down resistors that might contend with the driver.)
Applications
Utility Metering: Tamper detection in water, gas, and electric meters.
Consumer Electronics: Lid closure detection (Open/Close) for laptops and TWS earbud cases.
Medical Devices: Medication delivery tracking in battery-powered handhelds.
Industrial Automation: Pneumatic cylinder position sensing and non-contact limit switches.
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