MERCURY MR50-S3 Single Card Reader Interface Controller - Compact Door

Our review of the MERCURY MR50-S3 finds it a concise, practical controller for installers who need a small-footprint board that handles a single door reliably. The MR50-S3 is best for technicians and integrators seeking a compact interface that supports modern reader protocols without excess features. The single biggest reason to buy is its protocol flexibility: it accepts OSDP, Wiegand, clock/data, magnetic stripe, F2F and keypad or biometric inputs, making it a versatile choice when pairing different reader types with HID Mercury intelligent controllers.

Key Features

• 1 Reader Port: Supports up to two OSDP readers so installations requiring primary and secondary reader inputs are covered without extra hardware.
• Protocol Flexibility: Accepts OSDP, Wiegand, clock/data, magnetic stripe, F2F and supervised F2F to accommodate a wide range of legacy and modern readers.
• Door I/O: Provides the necessary relays and supervised inputs to control one door with tamper detection and multiple input points for sensors or switches.
• Compact Footprint: The small board size makes it easy to install in cramped backboxes or shallow enclosures where space is limited.
• RS-485 Connectivity: Connects over RS-485 for clustering or distributed topologies, simplifying wiring for multi-panel systems.
• Easy Integration: Designed to connect directly to HID Mercury intelligent controllers, streamlining integration into existing systems.

Who It's For

The MR50-S3 is aimed at security integrators, electricians and IT staff installing single-door access control where a compact interface is required. It is particularly useful in retrofit projects that mix reader technologies, since the board supports both legacy clock/data and modern OSDP readers, enabling phased upgrades without replacing wiring or host controllers.

It is less appropriate for projects that need multi-door control from a single board or where on-board advanced logic and many auxiliary outputs are required; larger Mercury controllers would be a better fit in those cases.

Pros & Cons

Pros

• Supports multiple reader protocols, offering flexibility during upgrades or mixed-reader deployments.
• Small footprint simplifies installation in tight enclosures and retrofit locations.
• Includes required I/O for a single door: relays, supervised inputs and tamper detection, reducing the need for extra modules.
• RS-485 connection allows clustering or distributed topologies with HID Mercury controllers.

Cons

• Limited to control of a single door, so larger installations will require multiple boards or a different controller.

Specifications

Brand	MERCURY
Model	MR50-S3
Reader Ports	1 port (supports up to 2 OSDP readers)
Supported Protocols	OSDP, Wiegand, clock/data, magnetic stripe, F2F, supervised F2F, keypad
Door Control	Controls 1 door
I/O	3 inputs (2 general purpose, 1 dedicated tamper), 2 relays (1 x NO 5A @30VDC or NC 3A @30VDC, 1 x 2A @30VDC)
Communication	RS-485

Our Verdict

The MERCURY MR50-S3 is a sensible, cost-effective choice for single-door access control when protocol compatibility and compact size matter. Integrators will appreciate the mix of supported reader interfaces and the included I/O for a complete door solution, making it good value for retrofit and small installations that pair with HID Mercury controllers.

Frequently Asked Questions

Can this board work with OSDP readers?
Yes. The MR50-S3 supports OSDP and can accommodate up to two OSDP readers on its single reader port.

How many doors can this controller manage?
It is designed to control one door; larger installations will require additional MR50-S3 units or a multi-door controller.

Does it connect to Mercury controllers?
Yes. The board easily connects to HID Mercury intelligent controllers via RS-485 for clustered or distributed deployments.