Vibration motors are the silent workhorses behind tactile feedback in wearables and handheld devices. These compact actuators convert electrical signals into physical cues, enriching user interaction. Whether you are prototyping or troubleshooting, understanding their behavior and integration is key to designing responsive, reliable hardware.
Let’s start with the basics: How they generate vibration, and what sets different types apart.
ERM and coin vibration motors
As is often valuable to design engineers, vibration motors can be categorized by form factors to simplify selection and integration. The two primary types are eccentric rotating mass (ERM) vibration motors and coin vibration motors.
ERM vibration motors generate vibration by spinning a mass that is offset from the center of rotation. This off-center mass creates an imbalance, producing the desired vibration effect. These motors typically have a cylindrical form factor, with the rotating shaft and eccentric mass often exposed. Their design is straightforward and well-suited for applications where space constraints are less critical.
Coin vibration motors, sometimes referred to as “pancake” motors, also rely on an offset rotating mass to produce vibration. However, they feature a flat, compact, and fully enclosed form factor. Internally, they contain a short shaft and a flat mass that is offset from the center of rotation, allowing the mechanism to fit within the coin-shaped housing.
Although coin motors operate on the same ERM principle, industry convention typically distinguishes them by form: the exposed cylindrical type is commonly referred to as an ERM vibration motor, while the flat, enclosed type is known as a coin or pancake vibration motor.
Figure 1 ERM and pancake vibration motors generate haptic feedback via eccentric rotating mass. Source: Author
LRA vibration motors
While our primary focus has been on vibration motor form factors, there is another important category worth highlighting: linear resonant actuator (LRA) vibration motors. In terms of external appearance, LRAs often resemble coin vibration motors, sharing the same flat, compact form factor. This visual similarity can be misleading, as the underlying mechanism is fundamentally different.
Unlike ERM motors, which rely on a rotating offset mass driven by a unidirectional current, LRAs operate using a linearly oscillating mass. This mass moves back and forth in a controlled manner, following the principles of simple harmonic motion. Because the direction of movement continuously changes, LRAs require an alternating current (AC) signal with a specific frequency that matches the resonant frequency of the actuator.
This distinction in operating principle allows LRAs to deliver more precise and efficient haptic feedback, making them well-suited for applications where responsiveness and control are critical. Despite their similar form factor to ERM and coin motors, LRAs represent a distinct class of vibration technology.
Figure 2 LRA vibration motor generates haptic feedback via resonant linear actuation. Source: Author
Keep note that there is also a growing category of brushless vibration motors, typically based on brushless DC (BLDC) technology. These motors offer improved durability and efficiency compared to traditional brushed ERM designs, thanks to the absence of mechanical brushes.
While they may share similar cylindrical or coin-like form factors, their internal construction and control requirements differ. Brushless vibration motors are especially useful in high-reliability applications where splendidly long mean time before failure (MTBF) and low maintenance are priorities.
Figure 3 BLDC motors often feature additional wires that enable functions like speed regulation and directional control. Source: Author
How to use actuators
Up next, we take a closer look at how to use these tiny actuators effectively in your designs.
To start with, ERM and coin vibration motors that run on DC can be powered directly from a suitable DC source. But when it comes to haptics—where you want the motor to respond to input—you will probably want to hook it up to a microcontroller. That way, you can control not just the on/off state but also tweak the amplitude and define vibration profiles.
For those seeking integrated driver solutions, ICs such as the NCP5426 offer a reliable and efficient alternative to using a simple BJT or MOSFET.
LRAs, on the other hand, operate on an AC signal and are tuned to a specific resonant frequency. Driving them properly usually means using a dedicated LRA driver to ensure optimal performance.
At this point, it’s worth noting that the DRV2605/DRV2605L from Texas Instruments is a popular motor driver designed for haptic feedback applications. Unlike basic motor drivers, it can generate nuanced vibration patterns, making it ideal for creating tactile feedback that feels responsive and intentional. Thus, it offloads waveform generation from the host processor, simplifying design and saving resources.
Quick note: After reviewing numerous datasheets, a few general trends emerge. Most ERM vibration motors are rated around 3 V, with a starting voltage near 2.5 V and a rated current close to 100 mA at full voltage.
In contrast, most LRAs tend to have a rated voltage of approximately 2 V RMS, a nominal operating current around 150 mA, and a resonant frequency of 150 Hz ±5Hz. That said, consider these figures as ballpark estimates rather than absolutes. Always double-check with the specific datasheet!
Other design considerations
When it comes to mounting vibration motors, they are typically placed within an enclosure or directly onto a PCB. For enclosure-based setups, custom 3D-printed housing can be a convenient way to fasten the motor. If you are mounting the motor to a PCB, many models offer through-hole pins for straightforward soldering. For coin and LRA types, the adhesive backing is usually sufficient for reliable attachment.
As a little extra, here is a handy blueprint for testing/driving a 6-wire vibration motor with integrated driver (Model NFP-BLV3650-FS, for example)
Figure 4 This handy little circuit tests and runs most vibration motors with internal drivers. Source: Author
Just to round things off, there are numerous ways to integrate haptic feedback into your devices, with vibration motors being one of the most accessible options. Whether you opt for a simple implementation or a more sophisticated approach, adding haptics can significantly elevate your device’s user experience and overall effectiveness.
The insights shared here are intended to serve as a springboard, hopefully helping you incorporate haptic feedback into your designs with confidence and creativity.
T. K. Hareendran is a self-taught electronics enthusiast with a strong passion for innovative circuit design and hands-on technology. He develops both experimental and practical electronic projects, documenting and sharing his work to support fellow tinkerers and learners. Beyond the workbench, he dedicates time to technical writing and hardware evaluations to contribute meaningfully to the maker community.
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