TECHNICAL SUPPORT
Published 2026-04-10
A serialservoexpansion board is a hardware module that connects to a microcontroller via a single serial (UART) interface and allows you to independently control multiple standard PWMservos. Instead of using many GPIO pins and complex timing, you send simple text or binary commands over RX/TX lines, and the board translates them into precise PWM signals for eachservo. This guide provides step-by-step instructions, real-world examples, and best practices to help you select, wire, and program a serial servo expansion board effectively.
When you build a robot arm, a hexapod walker, or a pan‑tilt camera mount, you often need to control 6, 12, or even 24 servos simultaneously. A typical microcontroller offers only a handful of PWM‑capable pins, and software‑based PWM often jitters. A serial servo expansion board solves both problems:
Reduces pin usage– Only one UART (TX/RX) or I²C connection is required, regardless of how many servos are attached.
Stable, hardware‑based PWM– Each servo receives a dedicated, jitter‑free signal.
Simplifies code– Instead of managing timers and pin states, you send a short command like#1P1500T100(servo 1, position 1500 µs, time 100 ms).
These boards typically come with an onboard microcontroller (e.g., ARM Cortex‑M0 or AVR) that handles all real‑time PWM generation, freeing your main MCU for higher‑level tasks.
Case 1 – 6‑Axis Robot Arm
A hobbyist built a desktop robotic arm with six servos (shoulder, elbow, wrist, gripper). Initially, he tried driving all six directly from a single development board, but the board froze when three servos moved at once due to current spikes and CPU overhead. After switching to a serial servo expansion board (with a separate 5V/5A power supply), the arm moved smoothly, and the main board only sent serial commands.
Case 2 – 12‑Servo Hexapod
A student team created a hexapod robot requiring 12 servos (2 per leg). They needed precise, simultaneous leg movements. Using a serial servo expansion board, they connected all servos to the board, powered it with a 6V/10A battery, and sent a series of position commands over UART at 115200 baud. The hexapod walked steadily, and the team reduced their code from 500 lines of manual PWM to just 50 lines of serial writes.
Case 3 – Automated Camera Slider
A videographer made a three‑servo camera slider (pan, tilt, zoom). He used a wireless serial adapter to send commands from a laptop. The expansion board provided jitter‑free movement,eliminating the vibration that ruined earlier footage.
These cases show that regardless of project scale, a serial servo expansion board is the reliable choice for multi‑servo control.
Before buying, evaluate these four criteria. They are derived from manufacturer datasheets and verified by community testing.
Common options: 8, 16, 24, or 32 channels. Choose one that exceeds your current need by at least 20% for future expansion.
Operating voltage– Most boards accept 5V–6V for standard servos (or up to 7.4V for high‑voltage servos). Check the board’s specification.
Current per channel– Continuous output per servo (often 1A–3A). Add the stall current of your servos (e.g., a standard micro servo may draw 0.5A idle, 1.5A stall). For 6 servos, a 5V/5A supply is the minimum.
The board itself usually doesnotprovide power to servos; you must connect an external power supply to the board’s “V+” and “GND” terminals. The logic (UART) side is typically powered by your microcontroller’s 3.3V or 5V.
UART (serial)– Most common. Uses TX/RX pins. Baud rates: 9600, 19200, 115200. Simple and reliable.
I²C– Shares the same two wires with multiple devices. Good for projects with many sensors.
USB– Some boards emulate a serial port via USB. Great for direct control from a PC.
Look for a board with a clear, documented protocol. For example:
Position command – #(e.g.,#3P1500sets servo 3 to 1500 µs, neutral position).
Time‑based movement – #1P2000T500moves servo 1 to 2000 µs over 500 ms.
Query commands– Read current position or moving status.
Avoid proprietary or poorly documented protocols – they make troubleshooting difficult.
Follow this exact sequence to avoid damage.
Step 1: Disconnect power– Do not connect anything to a live supply.
Step 2: Connect the external power supply to the expansion board
Identify the terminal block: “V+” (or “VS”) and “GND”.
Connect a regulated DC power supply (e.g., 5V/5A for 6 micro servos).
Do notpower servos from your microcontroller’s 5V pin – it will overheat.
Step 3: Connect servos to the board
Each servo has three wires:
Brown/Black → GND on the board.
Red → V+ (servo power).
Orange/Yellow → Signal (PWM output pin, labeled 1, 2, …).
Insert them according to the board’s silkscreen. Some boards use a standard 3‑pin header (GND, V+, Signal).
Step 4: Connect UART between microcontroller and expansion board
Board’s TX → MCU’s RX.
Board’s RX → MCU’s TX.
Board’s GND (logic side) → MCU’s GND.
Note: If the board has separate logic and servo grounds, tie them together at a single point.
Step 5: Apply power– Turn on the external supply first, then connect the USB to your microcontroller.
Step 6: Verify communication – Send a test command using a serial monitor (e.g., “#0P1500” for channel 0, neutral). The servo should move to 90°.
The following snippet works on any platform that can send raw serial data. Assume you have initialized UART at 115200 baud.
// Move servo on channel 0 to 1500 µs (neutral)
void setServo(uint8_t channel, uint16_t pulseWidth) {
char buffer[20];
sprintf(buffer, "#%dP%04d\r\n", channel, pulseWidth);
serialWriteString(buffer);
}
// Smooth move: channel 0 to 2000 µs over 500 ms
void smoothMove(uint8_t channel, uint16_t targetPulse, uint16_t timeMs) {
char buffer[30];
sprintf(buffer, "#%dP%04dT%d\r\n", channel, targetPulse, timeMs);
serialWriteString(buffer);
}
// Example usage in main loop
void main() {
initSerial(115200);
setServo(0, 1500); // center
delay(1000);
smoothMove(0, 2000, 500); // move to 2000µs in 0.5 sec
}
Important timing – After sending a command, wait at least the specified movement time before sending another command to the same servo. Some boards have a status command (e.g., “Q”) to check if movement is complete.
Never connect or disconnect servos while the power is on – this can create voltage spikes that destroy the board’s driver transistors.
Use a separate power supply for servos. A microcontroller’s USB 5V can only handle ~500 mA, enough for maybe one small servo.
Add a fuse (e.g., 5A fast‑blow) between the power supply and the board to protect against short circuits.
If your board has a “V+” jumper (to optionally power the logic from the servo supply), remove it if your servo voltage exceeds 5.5V – otherwise you will damage the board’s logic chip.
A serial servo expansion board transforms a complex, pin‑intensive multi‑servo project into a clean, two‑wire serial communication task. By offloading real‑time PWM generation to a dedicated board, you gain stability, simplify your code, and protect your main microcontroller from electrical stress.
Actionable recommendations for your next project:
1. Count your servos and calculate total stall current. Add 30% margin.
2. Choose a board with at least 16 channels (even if you need only 6 today) and a documented UART protocol.
3. Buy an appropriate external power supply – regulated 5V or 6V with at least 5A for up to 10 standard servos.
4. Test one servo first using a serial terminal – never write a full program before verifying hardware.
5. Always power the servo board before or simultaneously with the microcontroller – never the other way around.
Implement these steps, and you will have a reliable, scalable servo control system ready for any robotic application.
Update Time：2026-04-10
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