• Product: q.bit modular educational robotics controller
• Status: Draft — schematic implementation starting
• Purpose: ESP32-S3 controller and shared power/data backplane for eight removable modules.

• Educational and modular robotics development.
• Removable modules attach vertically to magnetic pogo docking zones.
• Production-intent SMT assembly with repeated docking cycles.

• Accept USB-C power and support native ESP32-S3 USB programming.
• Supply a regulated shared 5 V rail operated under a 6.8 A firmware allocation; the power stage remains an 8 A-class design target but does not provide a guaranteed 7.5 A or 8 A hardware ceiling.
• Protect each modular port with an approximately 2 A current limit.
• Provide shared 3.3 V I2C SDA/SCL and one dedicated SIG line per port.
• Provide WiFi and BLE through the ESP32-S3 module.

• ESP32-S3-WROOM-1-N8R8.
• Eight identical 5-contact magnetic pogo connectors in a 4 × 2 top-side grid.
• One top-edge USB-C connector; all other components mounted underneath.
• Six-layer controlled-impedance PCB.
• Side-accessible RESET and BOOT controls.

Diagram

• One USB-C receptacle on the top edge.
• CH224K requests a 20 V fixed PD profile.
• USB D+/D- connect to ESP32-S3 native USB through ESD protection and optional series damping resistors.
• Input protection includes VBUS TVS, fuse/eFuse and bulk capacitance.

• Target output: 5 V with a 6.8 A firmware-controlled operational allocation. The hardware is an 8 A-class design target, not a guaranteed 7.5 A or 8 A current ceiling.
• Preliminary implementation: LM5148 synchronous buck controller with external MOSFETs, designed from 20 V PD input.
• With the actual 6 mOhm shunt/current-sense network, estimated LM5148 equivalent DC current-limit onset is 7.34-11.79 A (9.40 A typical). This is an onset estimate, not a guaranteed output-current or short-circuit ceiling, because the relevant comparator/propagation delay lacks a guaranteed maximum.
• At 90% efficiency and the 6.8 A allocation (34 W output), expected 20 V input current is approximately 1.89 A; a 20 V / 3 A or better PD source remains recommended for transient and conversion margin.
• The originally proposed TPS563201 is retained only as a possible low-power logic regulator candidate; it cannot generate the high-current 5 V actuator rail.

• One independently current-limited 5 V eFuse/load switch per port, nominal limit 2 A.
• Firmware must enforce the 6.8 A global operational allocation and must not assume all eight ports can simultaneously draw 2 A. The present LM5148 network does not guarantee a precise aggregate hardware ceiling.
• Fault reporting and controllable enable are preferred.

• Separate 3.3 V regulator for ESP32-S3 and logic, sized for at least 1 A peak with appropriate transient margin.

• ESP32-S3-WROOM-1-N8R8 with native USB programming.
• Shared I2C bus with one pull-up pair near the MCU.
• Eight independent protected SIG GPIO lines.

1. 5 V protected output
2. GND
3. SDA (3.3 V I2C)
4. SCL (3.3 V I2C)
5. Dedicated SIG

• External USB-C PD source only; no battery in the current scope.
• Required adapter profile: 20 V / 3 A minimum recommended.
• 5 V operational allocation: 6.8 A total under firmware management, with approximately 2 A intended per active port. No guaranteed 7.5 A or 8 A aggregate hardware ceiling is claimed.
• Logic must remain stable during servo transients and port faults.

• Six-layer PCB, nominal 1.6 mm FR-4.
• Matte black solder mask and light silkscreen.
• Top side contains only USB-C and eight pogo docking connectors.
• Bottom-side SMT electronics; assembly must support high-current thermal copper and via arrays.
• Selected pogo connector: SAMZO PR5L5015-5P-C-H, LCSC C41361293, specified 5 contacts, 12 V and 2 A contact rating.
• Exact footprint and magnet/mechanical geometry remain blocked pending an authoritative manufacturer drawing or datasheet.

• Native USB-Serial/JTAG programming through the USB-C connector.
• Side-accessible RESET (EN) and BOOT (GPIO0) buttons.
• Individual port enable/fault control where GPIO availability permits; otherwise use GPIO expanders only if required by final pin budget.
• Port-load scheduling/power management to enforce the 6.8 A operational allocation.

• Exact board size: 155 mm × 85 mm, rounded rectangular outline.
• Eight top-side docking zones arranged four columns by two rows.
• ESP32 mounted underneath at an edge with antenna facing outward.
• No copper, traces, vias, components, magnets or mounting metal in the module antenna keep-out on any layer.
• Low component-height and mechanical-clearance zones beneath docking hardware.

• Six layers selected for USB signal integrity, RF return paths and high-current power distribution.
• 20 V PD followed by a high-current 5 V synchronous buck is required to support the 6.8 A operational allocation with conversion and transient margin; direct 5 V USB-C is not suitable for this power architecture.
• USB-C is shared for power negotiation and ESP32 native USB data/programming.
• All non-docking electronics are mounted on the bottom.

• A 20 V / 3 A USB-PD adapter is available.
• The 2 A pogo rating applies to each electrical contact; the VCC contact operates at its stated limit and therefore has limited current margin.
• Modules tolerate shared 3.3 V I2C signaling and include unique addresses or otherwise avoid bus-address conflicts.
• SIG electrical direction is not yet fixed; protection will be selected once module behavior is confirmed.

• Replaced the stale 5 V / 8 A guarantee with a 6.8 A firmware operational allocation. The LM5148 current-limit onset is estimated at 7.34-11.79 A (9.40 A typical) and is not a guaranteed aggregate hardware ceiling.
• Changed board requirement from four to six copper layers.
• Selected SAMZO PR5L5015-5P-C-H / LCSC C41361293 pogo connector.
• Confirmed top-side restriction: USB-C and eight docking connectors only.