Arduino Uno Robot Driver Board

This driver board is designed for use with XGO-Duck.

Version: V1.0 · Schematic Interpretation Edition · 2026-09-28

1. Product Overview

This design is an expansion carrier board that connects to an external controller board through H1–H4 pin headers. The current schematic contains no MCU, processor, or wireless module; program execution, USB downloading, networking, and similar functions are provided by the external controller board.

Main features:

• External DC power input and slide-switch control.
• Conversion of the external supply into on-board 5 V and 3.3 V rails.
• A QMI8658A six-axis inertial sensor that provides acceleration and angular-velocity data over I²C.
• Conversion of the controller UART TX and RX lines into one half-duplex SIGNAL bus.
• Six three-wire ports connected in parallel, exposing GND, power, and SIGNAL for bus devices with compatible electrical characteristics and protocols.
• Two power LEDs: one for the post-switch supply and one for the on-board 5 V rail.

All six ports share one bus; they are not six independent UARTs or six independent PWM channels. The board also has no power bridge for directly driving bare motors.

2. Functional and Power Block Diagram

CN1 / DC1 external DC input (both connected in parallel to Power)
                   │
                  SW1
                   │
                VCC8.4V ─────→ Pin 2 of the six bus ports
                   ├─────────→ Pin 1 of H3
                   ├─────────→ D4 power indicator
                   │
             U2: H7651-50PR (linear regulator)
                   │
                 VCC5V ──────→ D3 power indicator
                   │
             Q2: AMS1117-3.3V (linear regulator)
                   │
                 VDD3V3 ─────→ QMI8658A, transceiver buffers, signal pull-up

H4.2 / TX0 ──→ Automatic direction control and transmit buffer ──→ SIGNAL
H4.1 / RX0 ←── Receive buffer ←────────────────────────────────── SIGNAL
H2.9 / SDA, H2.10 / SCL ←──── I²C ────→ QMI8658A

VCC8.4V is a net name that expresses the design intent; it does not mean that this point has a precisely regulated 8.4 V output. It is the external input voltage after SW1.

3. Power Input and Switch

3.1 Input Connectors

Verify the pin numbering of DC1 against the purchased part, footprint drawing, and continuity of the physical connector before determining the inner/outer plug polarity. Do not infer it from common DC-jack conventions alone.

CN1 and DC1 are directly connected in parallel; there is no power-priority selection or isolation circuit between the two inputs. TPS2116 is not used in this version. In normal use, power the board through one input connector only; do not connect two independent supplies at the same time.

3.2 SW1 Switch

When pins 2 and 3 are connected, Power is fed to VCC8.4V. When pins 2 and 1 are connected, this power path is disconnected. The actual ON/OFF direction depends on the installation orientation.

SW1 controls the external-input path described above. If the external controller board is powered through USB or another interface, turning this switch off does not necessarily mean that the entire system is unpowered.

3.3 On-board Regulation and LEDs

The LEDs show only that their respective power rails are present. They do not demonstrate voltage accuracy, load capability, or correct software operation.

The H7651 product table lists an 8.5 V voltage specification, which is close to the 8.4 V supply naming used in this schematic. Therefore, this board must not be treated as a general-purpose 9 V/12 V input board. The complete allowable input range must be confirmed using the specific IC documentation, supply tolerance, surge conditions, and load testing. [Reference S1]

Linear-regulator dissipation is approximately P = (Vin − Vout) × I. For example, dropping 8.4 V to 5 V dissipates about 0.34 W at 100 mA and about 1.7 W at 500 mA. A 1 A device rating does not mean that this board can continuously provide 1 A: sustained current depends on package, PCB thermal performance, and ambient temperature. A 3.3 V load also consumes part of the upstream 5 V regulator’s current budget.

The bus-device supply comes directly from VCC8.4V, bypassing U2. Its total current remains limited by the input connector, SW1, connectors, and PCB traces; the available information is insufficient to specify a board-wide current rating. This schematic shows no reverse-polarity protection, fuse, battery charger, or battery-protection circuit.

4. External Interface Definitions

All pin numbers in this section are schematic pin numbers. They are not necessarily the left-to-right order when viewing the physical board. Check the PCB’s pin-1 marking before connecting anything.

4.1 Six Bus-Device Ports

Like-named pins on all six ports are connected fully in parallel. Although U3–U5 use U reference designators, they are connectors, not driver ICs.

• SIGNAL is driven by 3.3 V logic and pulled up to VDD3V3 through R8 (10 kΩ).
• Connected devices must support the corresponding single-wire half-duplex communication method. Verify their logic-high threshold and return-signal voltage.
• SIGNAL is not an RS-485, CAN, or RS-232 electrical interface and must not be connected directly to any of those interfaces.
• When multiple devices share the bus, the protocol must support distinct addresses/IDs and prevent simultaneous device responses.
• The bus ports are not general-purpose three-wire PWM-servo ports; three wires alone do not establish compatibility.

4.2 Headers Connecting to the Controller Board

The current SchDoc does not connect on-board VCC5V or VDD3V3 to any other pins of H1–H4. “Not connected” means it is not connected to circuitry on this carrier board; it does not mean that the corresponding positions have no function on the external controller board.

Although the file name includes ArduinoUnoQ, this schematic does not provide the controller-side pin names, processor port numbers, or power specifications. Do not directly apply UNO R3, UNO Q, or other controller-board D0/D1 or VIN mappings merely based on header appearance. The connector definition for the corresponding controller board must be supplied during development.

5. Single-Wire Half-Duplex Communication Circuit

5.1 Component Roles

The enable polarities of SN1 and SN2 are based on the TI datasheets. [References S2, S3]

5.2 Automatic Direction-Control Operation

With the existing connections, the logic operates as follows (propagation delay ignored):

TXEN is therefore generated on-board and is not brought out to a controller GPIO through the headers. This version does not require software to control a separate TXEN pin.

The controller should use standard UART polarity, with the idle state high. Once transmission ends, keep TX0 high to release the bus and receive a peripheral response. Baud rate, parity, frame format, addressing, response delay, and checksum are not defined in the schematic and must be configured according to the target device protocol.

While a low bit is being transmitted, the RX0 buffer is high impedance. The controller RX input should be configured with an appropriate pull-up; software must not assume it will always receive a complete and accurate echo of its own transmission. Confirm the specific MCU input configuration against its port specifications.

Because the high level is established mainly by a 10 kΩ pull-up, bus capacitance, cable length, and the number of devices affect the rising edge. Confirm the maximum usable baud rate with an oscilloscope using the actual cable harness and load; do not infer it solely from the buffer IC speed.

6. QMI8658A Six-Axis Sensor

U1 measures three-axis acceleration and three-axis angular velocity. It can be used for attitude estimation, tilt detection, motion recognition, and vibration monitoring. A six-axis sensor has no magnetometer; sustained absolute-heading estimation needs an additional reference, and long-term heading drift cannot be eliminated using only six-axis data.

The 0x6A address is determined from the definition of SA0 high in QST QMI8658A Rev A. Verify it during development by performing an I²C scan and reading the device ID. [Reference S4]

C1/C2 and C3/C4 respectively form supply filtering/decoupling combinations. Firmware can read data by polling: initialize I²C → confirm the identification register → set range and output data rate → read raw data → convert according to the selected range → perform bias calibration and coordinate transformation.

The schematic library labels pins 10 and 11 as CS-AUX and SDO-AUX, whereas the QST Rev A pinout labels them RESV and RESV-NC. Before production, confirm reserved-pin requirements for the actual purchased version; do not treat the library names as available expansion functions. The sensor mounting direction and mapping to robot coordinate axes must likewise be confirmed from the PCB and physical hardware.

7. First Power-Up and Development Procedure

1. Verify the controller board and headers. Confirm that H3.1 corresponds to a controller-board power terminal that accepts external power; confirm the UART directions at H4.1/H4.2 and the I²C mapping at H2.9/H2.10. Confirm that controller logic is compatible with this board’s 3.3 V signals.
2. Do not connect motors or bus devices yet. Use only one external input and set the supply current limit to a low value appropriate for no-load debugging. Select the input voltage according to the allowable range of the final components and controller board; do not use an unverified 9 V/12 V adapter.
3. Turn on SW1 and measure. Check Power, VCC8.4V, VCC5V, and VDD3V3. Under normal conditions, the latter two should be close to 5 V and 3.3 V. Check regulator temperature rise and D3/D4.
4. Verify the IMU. Initialize the I²C controller actually mapped on the controller board, confirm acknowledgment at 0x6A, then read the ID and configure sampling parameters. Because INT is not connected, use polling first.
5. Verify one bus device. Power off before wiring; verify 1 = GND, 2 = power, 3 = SIGNAL, then power up. Configure the UART according to the device protocol. Start with low-risk commands such as reading status, and confirm normal reception.
6. Add devices one at a time. Configure a different device ID for each device and communicate in request–response order. Check bus waveforms, power-voltage drop, connectors, and regulator temperature rise.

Software is best divided into three modules: an IMU driver, a UART bus transport layer, and a device-specific protocol layer. The UART instance name and GPIO numbers must be determined from the controller-board mapping; this guide does not directly specify Serial, Serial1, or a particular MCU pin.

8. Supported Development Features and Current Limits

This schematic has no battery-level sensing, charge management, motor-current sensing, independent emergency stop, or per-port power-control circuit. Do not infer that these functions are present from the existing interfaces.

9. Information to Complete Before Release

This guide can be used to understand the interfaces and prepare development. Before it is issued as the final product manual, add the following:

• Exact external controller-board model and revision, header mapping, and allowable input voltage.
• Verified complete-board input range, logic-load current, total bus current, and temperature-rise test results.
• Power-jack polarity, SW1 direction, port-location photos, and pin-1 orientation.
• Target bus-device model, signal level, protocol, baud rate, and supported maximum device count/cable length.
• Actual purchased QMI8658A version, reserved-pin treatment, and installed coordinate axes.
• Consistency between the Q2 library’s SOT-89 annotation and the actual purchased AMS1117 part number, package, and pinout, as well as the regulator’s output-capacitor stability requirements.

10. References and Interpretation Method

• S1: Shanghai Siproin H7651 product information. Used to confirm that it is a linear regulator and the manufacturer-listed parameters; board-level capability still requires testing.
• S2: TI SN74LVC1G126 datasheet.
• S3: TI SN74LVC1G125 datasheet.
• S4: QST QMI8658A Rev A datasheet.