This post was written in collaboaration with Evan Sawyer
from the Haptics Team at Texas Instruments
Consumers today are seeking life-like experiences with their electronics, but in a world of touch-screens, confirmation of button presses, scrolls and other tactile inputs is often limited to audible or visual feedback. Texas Instruments offers a complete solution to demonstrate, develop, and evaluate haptics, a technology that provides tactile feedback through vibrations, which is gaining traction in the mobile, wearable, medical and electronic point of sale (ePOS) markets because of how it increases device usability and user satisfaction.
The DRV2605EVM-CT evaluation module (EVM) is a demonstration and evaluation platform for the DRV2605 haptics driver and comes complete with an ultra-low-power MSP430 microcontroller, an eccentric rotating mass motor (ERM), a linear resonant actuator (LRA), waveforms and capacitive touch buttons. While an ERM or LRA can be driven using a discrete solution, the DRV2605 has a range of features such as auto-resonance detection, automatic calibration, low-power modes and 123 built-in waveforms licensed by Immersion.
By handling the haptics functions within the DRV2605, the MSP430 MCU is free for other tasks including battery monitoring, handling capacitive touch buttons inputs, or controlling outputs such as LEDs. Since the DRV2605 only requires simple I2C or PWM communication, designs could easily be implemented using any MSP430 MCU. A unique combination would be pairing with the MSP430FR4x/FR2x microcontrollers to add a segment LCD display or leverage more button control thanks to the available 60 input/output pins.
Two features in particular, automatic overdrive/braking and resonance detection, provide the DRV2605 with a clear advantage over other haptics solutions. Automatic overdrive and braking for ERMs create crisper haptic effects by decreasing the time needed to start and stop the motor. This is accomplished by providing a higher initial voltage to start the motor and high reverse voltage to stop the motor. LRAs can be difficult to use due to their narrow operating frequency range (~10 Hz wide) and a resonant frequency which drifts due to manufacturing tolerance, temperature, device position, etc. In fact, the vibration strength decreases by 40% if the LRA is driven a mere 3.5 Hz off of its resonant frequency. The DRV2605 automatically detects the resonant frequency to provide the strongest haptic effects.
The brain of this particular EVM is an MSP430G2553, a member of TI’s ultra-low-power microcontrollers which provide great features at an awesome price. These low cost 16-bit microcontrollers operate at speeds up to 16 MHz and extend battery life in portable systems through instant wake-up and various low-power modes. They come with 0.5 to 56 kB of flash memory and special features like capacitive touch I/O, watchdog timers, real time clocks, brownout detection and more. If a lower power or lower memory option is desired, the MSP430FR4133 or MSP430FR2033 could be a perfect fit! They provide up to 16 KB of FRAM, which provides real system advantages, including enhanced security and the ability to store state information in the event of a power failure.
There are two ways to control the DRV2605 with the MSP430. The first is through I²C where the MCU tells the driver which waveform to play. The second method is a PWM signal created by the microcontroller which is translated by the driver into a custom waveform. The advantage of the first method is that it offloads the storage of waveforms and the processing needed to drive a haptics effect to the DRV2605, freeing MCU memory and allowing it to perform other processes. The MSP430 can also be re-programed with custom code so that this haptics EVM can be integrated and tested in an existing system. Sample code for controlling the DRV2605 using an MSP430, along with software and GUI-based coding and debugging tools can be found online.
Are you interested in programming your own haptics effects? We have a solution for that as well! By pairing the simpler DRV2603 haptics driver with the MSP430TCH5E, developers can access 122 different haptics effects using industry-leading Immersion TouchSense 2200 haptic technology with licenses included. With this particular microcontroller, more flexibility is provided to create custom effect sequences (like a dice role or heartbeat effect) by chaining effects together and inserting delays. This MCU also provides the audio-to-haptics feature in which haptic vibration can be synchronized to a music source to create the ultimate user experience in gaming and personal entertainment applications.
Check out ti.com/haptics for more information or to order the DRV2605EVM-CT, the DRV2605 or the new haptic Bluetooth kit (DRV2605EVM-BT) which demonstrates haptics in wearable electronics. For evaluation of the MSP430TCH5E, try out the HAPTOUCH BoosterPack. You can also visit the haptics forum for design assistance. TI Designs also contain schematics, block diagrams, test data and system reference designs for simplifying haptics integration into your system!