Quickly (100Hz or more) blinking of camera flashlight LED

Question

I am trying to write a variable brightness flashlight app by using PWM (might use it for communication later). For that I need fast switching of the camera LED (say 100-200Hz), which is not possible through the Camera API's setParameters functionality (I guess the camera itself slows things down considerably).

Now – The LED is capable of switching rapidly and there are apps doing something similar (HTC flashlight for example, unfortunately couldn't find source code for it) so it all comes down to controlling the LED without the camera.

Any thoughts or ideas?

Answer 1

I know this is 4 years later, but you'd need a lot more than 100-200hz for PWM to work properly, without irritating the eye. You might get some control, but you won't be able to get 10% brightness without the pulses becoming noticeable, and even then, the duration of those pulses is too long to fool the eye. Typically PWM is handled at the microsecond level, around 100khz. I would like this to be possible as well. Except, if we could have say a 100khz carrier frequency in the flash, it would be possible to calculate distance to a subject with dedicated pixels in the sensor, as well as reject all ambient light through demodulation, if all pixels could be scanned fast enough. Sadly not possible though.

Answer 2

Normally to do that there'll be a PWM peripheral in the processor that handles the rapid switching for you, but that would need driver support; it won't be accessible to user applications. Here's a question which uses the driver to do it: Set brightness of flash in Android