• Status: Draft
• Device: 10×10 monochrome red LED matrix module.
• Purpose: Display externally generated patterns using multiplexed row drive and constant-current column sinks.

• Prototype/display module controlled by an external MCU.
• 5 V powered; logic inputs compatible with 3.3 V or 5 V controllers.

• Independently control 100 red LEDs arranged as 10 rows × 10 columns.
• Refresh one row at a time using a 4-bit row address and row-enable signal.
• Load column data through a cascaded serial LED-driver chain.
• Default to a blank display when the controller is absent or starting.

• 100 monochrome red SMD LEDs.
• 10 mm LED pitch target for PCB layout.
• Two cascaded 16-channel constant-current sink drivers.
• Ten P-channel MOSFET high-side row switches.
• 4-to-16 HCT decoder for row selection.
• 3.3 V/5 V-compatible external control interface.
• 5 V terminal-block input with resettable fuse and bulk decoupling.

Diagram

• Power: 5 V input, 500 mA resettable PTC, local bulk and ceramic decoupling.
• Column drive: Two STP16CP05 constant-current sink drivers at approximately 20 mA peak per active LED.
• Row drive: Ten P-channel MOSFETs selected by a 74HCT154 decoder.
• Logic interface: Buffered DATA, CLK, LATCH, and OE/BLANK plus row address and enable signals, with 4.7 kΩ input series protection.
• Display: 100 red LEDs, logically grouped into ten rows and ten columns.

• Power connector: +5 V and GND.
• Controller header: GND, DATA, CLK, LATCH, OE/BLANK, ROW_A0–ROW_A3, ROW_EN, 3.3 V-safe serial data output, and spare pins.

• External regulated 5 V source.
• One selected row at a time.
• Up to ten LEDs active in the selected row.

• Input protection is sized at 500 mA hold current to provide startup and tolerance margin.
• Each LED has about 2 mA average current at 1:10 multiplexing when programmed for 20 mA peak.

• SMD logic, drivers, MOSFETs, passives, and LEDs.
• Through-hole power terminal and controller header.
• PCB layout to maintain 10 mm center-to-center LED spacing.

• Shift 32 serial bits per display update; only ten assigned column bits are used.
• Blank outputs while changing row address and column data to avoid ghosting.
• Valid row addresses are 0–9; addresses 10–15 must remain blanked.

• LED centers on a 10 mm square grid.
• Approximate illuminated area: 90 mm × 90 mm between outer LED centers.
• Final board outline will be selected during PCB layout; a custom outline is preferred.

• Red LEDs are assumed because monochrome color was unspecified.
• Two cascaded drivers are retained per the confirmed default, despite unused output capacity.
• HCT logic is used so 3.3 V MCU signals are valid while the board operates from 5 V.

• External controller provides 3.3 V or 5 V push-pull logic and holds its outputs low or high-impedance when the matrix board is unpowered.
• BLANK and ROW_ENABLE_N default inactive using local +5 V pull-ups.
• Firmware provides 2–5 µs blanking/dead time around row changes.
• Refresh timing and PWM brightness are implemented in firmware.
• 20 mA is a peak multiplex current, not continuous average current.

• Initial schematic architecture established from the confirmed defaults.
• Added 4.7 kΩ protected controller inputs, 470 Ω PMOS gate resistors, local +5 V fail-safe pull-ups, and a 3.3 V-safe SDO divider after electrical review.