DLP Pico Projector Development Kit

Frank,

The video frame rates use the standard industry protocols such as NTSC (60Hz) and PAL (50Hz) with sync signals that follow the protocol. The DMD pattern rates are special timing sequences that are made specifically for applications that require faster frame rate. When one of those timing sequences (or display modes) is selected, the input can accept more frames per second with a decreased bit depth.

For example, one of the pattern rate is 240Hz. The diagram attached shows timing of system inputs and outputs. The top line shows RGB data input to the projector, coming in via the HDMI port. The next line shows the sequence of light pulses that come out of the projector. For example, the "B5" field is the pulse associated with HDMI input port "blue(5)", "R3" is HDMI input "red(3)", etc. With this display mode, there is a one to one mapping of input port bits to corresponding light output pulses per pixel – all inputs map to a single light pulse timeslot. The table below defines the display time for each light pulse. AUXSYNC3 output is a camera sync timing strobe, that is adjustable in both delay and pulse width. This signal is an output from the projector, configured via I2C commands contained further down in this example procedure.

More information on these DMD pattern rates (or display modes) will be available online in the very near future.

The light output is 10 lumens on the Pico. A higher powered LED will not be able to increase the light output due to the principle of etendu. (You could find out more information on etendu at http://en.wikipedia.org/wiki/Etendue). Also, there is a limit on the amount of current that can drive the LED. Over-current of the LEDs may result in device degradation.

Thank you for helping me get a better understanding of the pattern rates.  To make sure I am understanding everything correctly please let me know if my following paragraph is accurate.

In the period of 16.667ms each of the LED's R-G-B flash 4 times. On top of that the mirrors can either be in the on or off position for .90 and then .45 milliseconds which varies the perceived intensity of each specific LED.  This all blurs together in a frame of a pixel to produce a certain color.

Now if the pattern rate is increased from 60 to 240 is the bit depth decreased from 8 to 2 bits per color?  Or can the mirror cut its first display time from .90 ms in half to slightly increase the amount of data to 3 bits per color at 240 Hz?  What I need to know is how the 120Hz, 180Hz, and 240Hz refresh rates relate to bit depth.

Additionally can the position of each bit in the projected sequence of images, and display time per bit be adjusted?  I will potentially be using this to test a very sensitive light sensor, and need to know the frequency and timing at which the mirrors turn on and off, and if this frequency, and pulse width can be varied by a specific input.

Thank you again for your help, and I will be looking forward to your response.

Frank Regan

Frank,

The Digital Micromirror Device (DMD) uses pulse width modulation (PWM) to achieve various levels of light intensity on each of the pixels in the DMD array. By turning a pixel mirror on and off in response to data bits at a rate faster than the human eye can perceive, the pixel appears to have an intermediate intensity proportional to the fraction of time the mirror is on.

By switching between the RGB light, it effectively produces the different colors.

There is a trade off between the bit-depth and the DMD pattern rate in the Pico V2.0. The time each pixel is on or off can not be changed outside of what is available on the Pico. What I showed above was one of the DMD pattern rates available. There is an app note that should be coming online in the very near future that explains the different DMD pattern rate options available in the Pico with the appropriate bit-depth. If you need more information on the app note, please send me a friend request.

The time it takes for each pixel to process can not be changed outside of the 8 non-display pattern rate. There is a description in the app note to what the DMD pattern rate is for each display mode including an explanation of what the timing is for each bit.

This is very helpful, thank you.  I wonder how the led firing pattern for this patterned illumination mode compares to the firing pattern in normal video mode.  I know with a color wheel DLP there are RGB sequences followed by a white sequence, but presumably this kind of sequencing isn't necessary with an RGB LED light source?  Is there an application note explaining the LED firing for video mode?