Magnetic Bzr
A magnetic sound component converts changing magnetic excitation into sound. An internally driven indicator can operate from its specified DC supply; an externally driven transducer requires the prescribed time-varying drive. Neither its size nor its appearance establishes those requirements.
Electrical current creates a changing magnetic field that moves the sound-producing structure. Built-in drive circuitry provides this excitation in an active indicator. The CMI-1210-90-SMT-TR is a documented internally driven example, but its datasheet does not establish one universal internal transistor or feedback-winding circuit for all magnetic buzzers.
In plain terms
An electrically controlled magnetic pull moves a sound-producing element. A built-in driver can provide the repeated pulls, or the external circuit can supply them.
Why designers use it
- Providing an audible indication with a selected tone and sound level.
- Choosing an internally driven part when a simple supply-controlled tone is suitable.
Best for
- Audible status
- Equipment indicators
- Documented alert requirements
Key specifications
- Example rated supply: CMI-1210-90-SMT-TR: 5 VDC
- Example operating supply: CMI-1210-90-SMT-TR: 4–7 VDC
- Drive type: Identify internal or external drive from the actual datasheet
- Acoustics: Use the specified frequency, supply and measurement distance
When not to use it
- When the chosen component's current, acoustic output or environmental ratings are unsuitable.
- As evidence that a smoke alarm, medical alarm or other safety system meets its requirements without product-level validation.
Common mistakes
- Applying steady DC to a transducer that requires an external alternating drive and expecting a continuous rated tone.
- Assuming a magnetic indicator is always louder or more efficient than every piezo design.
- Ignoring the specified measurement distance when comparing sound-pressure levels.
- Copying a transistor or suppression circuit without checking the actual sounder's drive requirements.
Where you will find it
- Same Sky documents the CMI-1210-90-SMT-TR as a magnetic, internally driven surface-mount indicator. Its rated supply is 5 VDC and operating range is 4–7 VDC.
- A circuit designer can select an indicator for a status beep after checking the actual tone, current and acoustic test conditions, without assuming it is certified for life-safety use.
A short history
The drive arrangement is separate from the magnetic actuation mechanism. Manufacturer documentation explicitly identifies internally driven magnetic indicators, so 'magnetic buzzer' does not necessarily mean the external circuit must generate the tone waveform.
Good to know
- A built-in driver is a feature of a particular sounder, not proof that the element is piezoelectric.
- A small sounder alone does not establish compliance of an alarm system.