Yes—you can control a hobby servo from a phone over Bluetooth with an Arduino. The phone sends a text command, a Bluetooth module presents that data on a serial connection, and the Arduino sketch validates the value before the Servo library moves the motor. This guide covers a one-servo build, the HC-05/HC-06 Classic Bluetooth approach, the HM-10 BLE alternative, safe power wiring, and a command format that is less fragile than simply calling parseInt().
How the project works
The signal path has three stages:
- The phone app sends a numeric command such as
90, followed by a line terminator. - The Bluetooth module transfers that text to the Arduino UART or a software serial port.
- The Arduino parses the number, checks that it is valid, and calls
servo.write(angle)for a positional servo.
Bluetooth does not drive the motor directly; the Arduino remains responsible for interpreting commands and generating the servo control signal.
Choose compatible parts before wiring
- An Arduino-compatible board and USB cable for uploading the sketch.
- A positional hobby servo rated for the voltage, current, travel, and mechanical load you need.
- Either an HC-05/HC-06 Classic Bluetooth module or an HM-10 BLE module.
- A phone app that supports the selected Bluetooth mode and can transmit text.
- Jumper wires and a regulated servo supply. Add a capacitor only when its voltage rating, polarity, and capacitance suit the circuit.
HC-05/HC-06 Classic Bluetooth and HM-10 BLE are not interchangeable connection paths. Select the module first, then use an app and Arduino serial arrangement that support that module’s mode. Breakout boards also differ in UART voltage limits and onboard regulation, so read the board documentation before applying the example wiring below.
Positional versus continuous-rotation servo
A positional servo uses an angle command; many examples accept 0–180 degrees. That is a common control convention, not a guarantee that every servo can physically reach both endpoints without binding. A continuous-rotation servo uses the same Servo library family but interprets commands as rotation speed and direction rather than an absolute shaft position. Use a positional model when the requirement is “move to 45°,” and a continuous-rotation model when the requirement is “turn forward or reverse.”
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One servo or several
One servo can be driven directly from an Arduino control pin. For several servos, plan the supply for their combined current and consider a PCA9685 16-channel PWM driver, as suggested by the reviewed Bluetooth tutorial. A driver does not remove the need for a correctly sized external power supply or a shared ground.
Power and wiring that will not reset the Arduino
Identify the selected servo’s leads from its documentation. The common convention is red for power, black or brown for ground, and yellow, orange, or white for signal. Connect the signal lead to the same Arduino pin named in attach(); pin 9 is only an example used in Arduino servo guidance.
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Servo current changes with size and load. Arduino documentation advises checking operating voltage, idle current, running current, and stall current rather than assuming the board’s 5 V rail is adequate. Its Feetech Mini Servo example is specified at 4.8–6 V, 5–6 mA idle, and up to 800 mA under load. Those figures describe that named servo, not every hobby servo. High load current is generally not safe to draw from an Arduino board.
Use a separate, regulated supply when the servo’s requirements exceed what the board can safely provide. Connect the external-supply ground to Arduino ground so the signal has a common reference. Arduino’s Servo documentation states: “Note that servos draw considerable power, so if you need to drive more than one or two, you’ll probably need to power them from a separate supply (i.e. not the 5V pin on your Arduino).” Arduino’s servo guidance gives 100 µF as a capacitor recommendation for its named Feetech mini-servo example; use that value only when appropriate for your own supply and component ratings.
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- The SG90 has 3 wire interfaces: Red wire-5V, Brown Wire-Ground, Yellow wire-digital pin 9
Example connection map
The following is an implementation example, not a universal pinout:
| Connection | Example | Check before copying |
|---|---|---|
| Servo signal | Arduino pin 9 | Must match servo.attach() and the servo documentation. |
| Servo power | External regulated supply | Match the servo’s voltage and current, including load or stall demand. |
| Servo ground | External supply ground | Join it to Arduino ground. |
| Bluetooth TX | Arduino receive pin (for example, software-serial pin 10) | Confirm the module and serial-port mapping. |
| Bluetooth RX | Arduino transmit pin (for example, pin 11 through a voltage divider) | Check breakout input-voltage and Arduino logic-level limits. |
The cited HC-05/HC-06 project uses module TX to Arduino pin 10 and Arduino pin 11 to module RX through a voltage divider. Treat that as one build’s map: module breakouts and Arduino boards can require different levels, pins, or serial implementations.
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Use a clear command protocol
Make the phone send one integer per line, such as 0, 90, or 180, terminated by a newline. The sketch below buffers characters until a newline, rejects non-numeric input and values outside 0–180, then moves a positional servo. This avoids depending on a phone’s exact line-ending behavior or on parseInt()‘s timeout-based parsing.
#include <Servo.h>
#include <SoftwareSerial.h>
Servo servo;
SoftwareSerial bluetooth(10, 11); // Arduino RX, TX
const byte SERVO_PIN = 9;
String line;
void setup() {
servo.attach(SERVO_PIN);
servo.write(90);
Serial.begin(9600);
bluetooth.begin(9600); // use the module's configured baud rate
}
void loop() {
while (bluetooth.available()) {
char c = bluetooth.read();
if (c == 'n' || c == 'r') {
if (line.length() > 0) {
bool valid = true;
for (char ch : line) {
if (!isDigit(ch) && !(ch == '-' && line.indexOf(ch) == 0)) {
valid = false;
}
}
int angle = line.toInt();
if (valid && angle >= 0 && angle <= 180) {
servo.write(angle);
bluetooth.println("OK");
} else {
bluetooth.println("ERR: send 0-180");
}
line = "";
}
} else if (line.length() < 8) {
line += c;
} else {
line = ""; // discard an overlong frame
bluetooth.println("ERR: too long");
}
}
}Set bluetooth.begin() to the baud rate configured in your module; the sources do not establish one universal rate. If your phone app sends only carriage returns, configure the app accordingly or treat both r and n as terminators, as this example does. Do not combine a character-command protocol from one example with numeric parsing from another unless you document both formats and implement both branches.
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Pairing and operating the project
- Upload the sketch over USB with the Bluetooth module disconnected from any pins that interfere with uploading.
- Connect the servo signal, power, and common ground; verify polarity before energizing the supply.
- Connect the module’s TX/RX according to its breakout documentation and the serial pins in the sketch.
- Power the Arduino and servo supply, then pair using a Classic-Bluetooth terminal for HC-05/HC-06 or a BLE-capable app for HM-10.
- Send a line such as
45followed by the configured terminator. The servo should move toward that command if it is a positional model and the value is accepted.
Classic Bluetooth and BLE: practical differences
| Question | HC-05/HC-06 Classic Bluetooth | HM-10 BLE |
|---|---|---|
| Phone connection | Use a Classic-Bluetooth serial terminal or equivalent. | Use a BLE app that can write to the module’s characteristic. |
| Arduino-side data model | UART-style serial data on the module. | BLE characteristic writes are exposed by the module as serial data. |
| Main compatibility check | Phone OS support for Classic Bluetooth serial profiles and module voltage levels. | BLE support, app characteristic handling, and module firmware/configuration. |
| Pin map | Use the selected breakout’s TX/RX and logic specifications. | Use the selected breakout’s TX/RX and logic specifications. |
These are connection choices, not a universal performance ranking. Verify the exact board revision, module breakout, phone, and app before finalizing a bill of materials.
Quick Recap
Troubleshoot in this order
- No movement: confirm the servo has power and that signal, ground, and power leads match its documentation.
- Wrong pin: compare the physical signal wire with the pin passed to
attach(). - Resets or jitter: test the servo on a supply that meets its loaded current requirement; use a shared ground and appropriate supply decoupling.
- No Bluetooth data: check TX-to-RX crossing, the selected serial port, logic-level compatibility, pairing mode, and module baud rate.
- Commands rejected: make the phone send plain decimal text with the terminator expected by the sketch; remove spaces or other characters unless the parser handles them.
- Servo binds or hums at an endpoint: reduce the commanded range and follow the servo manufacturer’s mechanical limits.
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