Example 22: Servo Control (SG90)

Experiment Overview

SG90 is a commonly used micro servo that controls rotation angle (0°~180°) via PWM signal. FastBee has a built-in PWM_SERVO peripheral type (type: 41), directly supporting angle control.

Hardware Wiring

Board Label	GPIO Pin	Connected Device
SIGNAL	GPIO17	SG90 signal line (orange)

SG90 wiring: Red→5V, Brown→GND, Orange→GPIO signal line.

JSON Configuration Example

{
  "peripherals": [
    {
      "id": "servo_01",
      "name": "Servo SG90",
      "type": 41,
      "enabled": false,
      "pins": [13],
      "params": {}
    }
  ]
}

Peripheral Execution Linkage

Scenario 1: Remote Angle Setting (Platform Trigger)

Function: Control servo to specified angle via cloud platform command

Web Interface Configuration Steps

Step 1: Create Rule

1. Click Peripheral Execution in the left menu
2. Click New Rule button
3. Fill in basic configuration:
   • Rule Name: Servo to 90 Degrees
   • Report Data: ✅ Enable
   • Enabled: ✅ Enable

Step 2: Configure Trigger

1. Click Add Trigger button

2. Fill in trigger configuration:

   Field	Value	Description
   Trigger Type	Select Platform Trigger	Receive cloud platform commands
   Operator	Select Set Mode	Received data as action parameters

Step 3: Configure Action

1. Click Add Action button

2. Fill in:

   • Action Type: Select Set Servo
   • Target Peripheral: Select servo_01
   • Action Params: 90 (angle, 0-180)

3. Click Save button

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Scenario 2: Button Controls Servo (Event Trigger + Script)

Function: Each button press increases servo by 30 degrees, cycling 0-180

Web Interface Configuration Steps

1. Create rule, name: Button Control Servo
2. Trigger configuration:
   • Trigger Type: Select Event Trigger
   • Event Type: 100 (GPIO interrupt)
   • Event Source: key1
3. Action configuration:
   • Action Type: Select Command Script
   • Action Params:

   var a=getVar('servo_angle',0);
   a=(a+30)%180;
   servoWrite('servo_01',a);
   setVar('servo_angle',a);

4. Click Save

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Scenario 3: Servo Scan Mode (Timer Trigger + Script)

Function: Servo auto sweeps back and forth (0°↔180°)

Web Interface Configuration Steps

1. Create rule, name: Servo Scan
2. Trigger configuration:
   • Trigger Type: Select Timer Trigger
   • Timer Mode: Select Fixed Interval
   • Interval Time: 50 (50ms refresh)
3. Action configuration:
   • Action Type: Select Command Script
   • Action Params:

   var a=getVar('scan_a',0);
   var d=getVar('scan_d',1);
   a+=d*2;
   if(a>=180){a=180;d=-1;}
   if(a<=0){a=0;d=1;}
   servoWrite('servo_01',a);
   setVar('scan_a',a);
   setVar('scan_d',d);

4. Click Save

SG90 Features

Feature	Parameter	Description
Angle Range	0° ~ 180°	Standard servo
Supply Voltage	4.8V ~ 6V	Recommend 5V
PWM Frequency	50Hz	Standard frequency
Pulse Width Range	500~2500μs	Corresponds to 0-180°
Torque	1.8kg·cm	Light load

Notes

1. Power: SG90 needs 5V/500mA power, do not power from ESP32 3.3V
2. Angle Range: SG90 range 0°~180°, exceeding will damage gears
3. PWM Frequency: Servo standard PWM frequency 50Hz, pulse width 500~2500μs
4. Jitter: Lower quality servos may jitter at certain angles, fine-tune pulse width range
5. Torque: SG90 torque 1.8kg·cm, excessive load will cause stall and heating
6. Multiple Servos: Multiple servos need independent power supply to avoid power fluctuations