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SFM-20B 85dB Active Buzzer Alarm — DC 3–24V, Continuous Sound, Arduino Industrial
SFM-20B 85dB Active Buzzer Alarm DC 3–24V, Continuous Sound, Arduino Industrial
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SFM-20B 85dB Active Buzzer Alarm — DC 3–24V, Continuous Sound, Arduino & Industrial
The SFM-20B is a high-decibel active buzzer alarm module rated at 85dB sound pressure level, operating from DC 3V to 24V. As an active buzzer, it contains an internal oscillator and produces a continuous tone immediately when power is applied — no PWM or frequency signal required from the microcontroller. With a wide 3–24V supply range and -40°C to +80°C operating temperature, it is suitable for Arduino alarm systems, industrial alert indicators, security panels, and any application requiring a loud, reliable audible alarm.
Key Specifications
| Parameter | Value |
|---|---|
| Model | SFM-20B |
| Type | Active buzzer (internal oscillator) |
| Sound Pressure Level | 85dB (at 10cm) |
| Operating Voltage | DC 3V – 24V |
| Rated Voltage | DC 12V (typical) |
| Current Consumption | ~30–50mA (at 12V) |
| Sound Type | Continuous tone |
| Frequency | ~2300Hz (internal oscillator) |
| Operating Temperature | -40°C to +80°C |
| Connection | 2-wire (+ and −) |
Active Buzzer vs Passive Buzzer
| Feature | Active Buzzer (SFM-20B) | Passive Buzzer |
|---|---|---|
| Internal oscillator | Yes — produces sound on DC power | No — requires PWM signal |
| Control | Simple ON/OFF (GPIO or relay) | PWM frequency control needed |
| Sound | Fixed frequency continuous tone | Variable frequency, melodies |
| Volume | Higher (85dB+) | Lower (typically 70–80dB) |
| Best for | Alarm, alert, industrial indicator | Music, variable tone, melody |
Why Choose SFM-20B?
- 85dB sound level — loud enough for industrial environments and security alarms
- 3–24V wide range — works from 3.3V (ESP32 direct), 5V (Arduino), 12V (industrial), and 24V (PLC)
- Active design — simple ON/OFF control, no PWM or frequency programming needed
- -40°C to +80°C — industrial temperature range for outdoor and harsh environment use
- Continuous tone — persistent alarm sound until power is removed
Compatible With / Common Use Cases
- Arduino alarm system: Drive via NPN transistor (BC547) or MOSFET from Arduino GPIO — GPIO HIGH triggers alarm
- Industrial alert indicator: 12V or 24V buzzer on PLC output for machine fault alarm
- Security panel: Door/window sensor alarm buzzer in home security system
- Temperature alarm: Trigger buzzer when temperature sensor exceeds threshold
- Power-on indicator: Brief buzzer beep on system startup for status confirmation
Frequently Asked Questions
Q: Can I drive SFM-20B directly from Arduino GPIO pin?
A: At 3–5V, the SFM-20B draws ~10–20mA, which is within Arduino GPIO limits (40mA max). However, for reliable operation and to protect the GPIO pin, use an NPN transistor (BC547, 2N2222) as a switch: GPIO → 1kΩ base resistor → transistor base; collector to buzzer negative; buzzer positive to 5V; emitter to GND. This allows the buzzer to draw current from the 5V rail, not the GPIO pin.
Q: How do I control SFM-20B with a relay module?
A: Connect the relay NO (normally open) contact in series with the buzzer power supply. When the relay coil is energized (by Arduino GPIO via relay module), the NO contact closes and powers the buzzer. This provides complete electrical isolation between the Arduino and the buzzer circuit, ideal for 12V or 24V industrial buzzer applications.
Q: Can I make the SFM-20B beep intermittently instead of continuously?
A: Yes — control the power to the buzzer with a transistor or relay driven by Arduino PWM or timed GPIO switching. Use digitalWrite(pin, HIGH); delay(500); digitalWrite(pin, LOW); delay(500); for 0.5s on / 0.5s off beeping. The buzzer itself always produces a continuous tone when powered — intermittent beeping is achieved by switching the power on and off.
Package Contents
- 1× SFM-20B 85dB Active Buzzer Alarm Module
