Self Calibrating Haptic Chip Uses Less Power

Self Calibrating Haptic Chip Uses Less Power

Smartphones and tablets are turning into interactive slabs but those smooth surfaces can provide more than visual feedback with the right haptic hardware. Texas Instruments' (TI) DRV2605 haptic controller with driver provides developers with an agnostic device that will handle linear resonant actuators (LRA) or or eccentric rotating motors (ERM). It comes in a low profile 1.5- by 1.5-mm WCSP (Fig. 1). and incorporates Immersion's haptic library.

Figure 1. Texas Instrument's DRV2605 haptics controller is only 1.5mm by 1.5mm.

The DRV2605 integrates a royalty free library to simplify design chores. It makes stringing a sequence of vibrations together easy (Fig. 2) using the I2C interface. Programmers need only specify the type of feedback and duration.

Figure 2. The DRV2605 can easily handle a sequence of vibrations to match user interactions such as sliding a button to unlock a phone.

Haptic systems can operate more efficiently if they are properly configured. The DRV2605 actually handles its own calibration dynamically using "auto resonance" to determine the optimum operating timing in under two cycles. This is important because a number of issues can affect this including the type of actuator, ambient environment and the age of the motor. TI used sensorless, back EMF feedback to track the actuator's operation and adjust its performance accordingly. It essentially tracks the ripples to determine when to overdrive and when to brake the device.

A calibrated system can deliver twice the vibrational strength using half the power of comparable devices. This makes it more power efficient. It can also make it quieter.

Android provides a basic API for haptic feedback that can be further enhanced by the DRV2605's effects library. There is also a lack of standard recipes for the kinds of feedback a user would expect from a particular on-screen action. TI provides the $99 DRV2605 Evaluation Kit (Fig. 3) that provides access to the wide variety of functions available with the Immersion library.

Figure 3. The DRV2605 evaluation board provides tactile feedback with capactive touch keys.

The evaluation software has a drag-and-drop interface for quickly testing the 123 haptic sequences using the capacitive touch keys. It also provides audio feedback. The board has an ERM and LRA actuator. An on-board TI MSP430 provides the control intelligence for the system.

The DRV2605 is available for $1.60 in 1K quantities.

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