After doing a bit of technical reading about the taptic engine, I am wondering if our frequency is wrong and that is why we are getting no effect. I found a Taptic Engine manufacturer and they listed the resonate frequency their engines operate at.
Here is the paragraph with the info…
“Our Linear Resonant Actuators (LRA) vibration motors are an excellent choice for haptic application requiring a device with high reliability and exceptionally long life LRA s have an internal mass that oscillates back and forth along the X-axis at its resonant frequency. They are an excellent alternative to the brushless vibration motors as the only internal parts that are subjected to wear / failure are the spring. Unlike conventional brushed DC vibration motors, linear resonant actuators must be driven by an AC signal at the devices resonant frequency. There are companies make IC drivers for linear vibration motors that supply the correct drive signals and contain a library of haptic effects you can choose from. TI company makes LRA drivers IC s. We can supply you with an evaluation board that incorporates the TI** DRV8601**,** DRV2603**, haptic driver IC. Contact us for info. It should be noted that unlike brushed ERM vibration motors, varying the amplitude of the applied voltage will only change the amplitude of the vibration force, not only the frequency of vibration. The frequency of vibration is fixed at the LRA s resonant frequency which in the case of our LRA s is either 180 or 200 Hz. Due the LRA s Hi-Q , applying a frequency above or below the resonant frequency of the LRA will result in the LRA producing a lower vibration amplitude or if far from the resonant frequency.”
So basically to get the haptics to work we have to vibrate the spring at the resonate frequency of the Taptic Engine. I’m going to try the recommended 180 or 200 hz above. I would think this means the frequency curve is actually a straight line for the duration of our effect. The amplitude adjusts the force and creates the pattern of the taps.