EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: rgujju on May 29, 2021, 11:45:14 am
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Hello everyone!
I am designing a smart watch and wanted to understand how to drive the motor.
Should I drive the vibration motor directly from battery or from the output of the LDO?
What would be the advantages and drawbacks of the choice?
What difference would one make over the other?
The other circuit requires about 60mA and the motor would require about 70-100mA.
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Does the motor run on steady DC
or does it need some kind of drive waveform?
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Run from the battery, with a LC filter on the motor supply, and extra filtering after your switch, which should include at least a transient suppression diode across the motor, along with some small ceramic chip capacitors close physically to the motor. Ceramic capacitor across the motor is not too critical, anything from 10-100n chip ceramic, and the LC filter as well is not too critical, just the coil must be well damped or a lossy ferrite bead type, so as not to make it a LC oscillator. Filter capacitor likely will be a high value chip ceramic type, so make sure to have some damping across the inductor to prevent making a high voltage spike that will damage the rest.
99% of small vibratory motors are brushed, and are electrically noisy, but also tolerant of wide supply voltage swings, so unregulated well decoupled supply is fine.
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Does the motor run on steady DC
It works on DC. Its a ERM motor.
Run from the battery
My concern about running from a battery is would the amplitude of vibration change due to drop in battery voltage from 4.2V to about 3.6V?
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Not going to change much, the vibration amplitude depends on the rotating eccentric mass, and does not change much with voltage, though the frequency will change with voltage, but for a vibrator you really do not care if it is 15H or 18Hz vibration, just that it vibrated for the brief periods you need it to.