DLP4500: How to program the DLP lightcrafter 4500 to repeat patterns during pattern sequence mode

Thanks for the reply!

I appreciate your idea of "create the bitplane sequence to display the desired pattern". But I am confused about " you are required to display all of the bitplanes before the next VSYNC".

Since VSYNC is from the computer graphic card at 60Hz, and the computer graphic input signal is only 24 bits (8R 8G 8B) between two adjacent VSYNC. Do you mean i should manually program the computer graphic card such that it repeats the 24bits three times between every adjacent VSYNC?

Is there a way that i can program the 4500 instead of the PC computer graphic card to achieve this same effect? In other words, program the 4500 such that it automatically repeats 24bits input stream in between two VSYNC three times while the PC graphic only input 24bits every 1/60s?

Great answer and thanks for the reply! Please allow me to clarity a little bit:

1. What do you mean by "slow down the input data"? By selecting video port and VSYNC, isn't it by default that the video input is 24-bit picture frames? The input rate seems to be fixed and non-adjustable.

2. By "entire pattern needs to be done in 1/60seconds", do you mean I should reduce the "pattern exposure time"? For example, if my pattern sequence is:

F0:R0 F0:R1 F0:R2 F0:R3 F0:R4 F0:R5 F0:R6 F0:R7 F0:G0 F0:G1 F0:G2 F0:G3 F0:G4 F0:G5 F0:G6 F0:G7 F0:B0 F0:B1 F0:B2 F0:B3 F0:B4 F0:B5 F0:B6 F0:B7 F0:R0 F0:R1 F0:R2 F0:R3 F0:R4 F0:R5 F0:R6 F0:R7 F0:G0 F0:G1 F0:G2 F0:G3 F0:G4 F0:G5 F0:G6 F0:G7 F0:B0 F0:B1 F0:B2 F0:B3 F0:B4 F0:B5 F0:B6 F0:B7 F0:R0 F0:R1 F0:R2 F0:R3 F0:R4 F0:R5 F0:R6 F0:R7 F0:G0 F0:G1 F0:G2 F0:G3 F0:G4 F0:G5 F0:G6 F0:G7 F0:B0 F0:B1 F0:B2 F0:B3 F0:B4 F0:B5 F0:B6 F0:B7

for a 60hz VSYNC 24-bit video input, then i should set the pattern exposure time to be 1/(60*24*3) = 231.48 us ? Since exposure time must be an integer, should i be 231 or 232 us?

Hello Song,

If you would like each 1-bit pattern to be displayed for 1/60 = 16.667ms and you have 24*3=72 patterns, your VSYNC should occur every 16.667*72 = 1200ms. Therefore, your video rate would be 0.83fps. If you are piping data directly from your computer this may not be supported. This is what I was talking about when I said slow down the input data.

Alternatively you may want to try exploring different ways to send the data by dividing it up in different frames to send and display. Keep in mind the 24-bit video frame you are sending is merely a representation of the data that can be displayed. The Lightcrafter 4500 will display whatever part of the frame you desire with regards to it being video data (ie. there is no requirement for the R bits to actually coorspond to red or for the bits to be displayed in order). I would definitely recommend downloading and using the GUI software to better understand how it works if you haven't been already.

Thanks,
Kyle

Hi Kyle:

Thanks so much for the patience and help!  I have downloaded GUI and played with it for quite some time and i still some of your help.

Sorry that i didn't make clear previously. The depicted scenario i mentioned above is:

1. Video input is simply a Windows PC hooked up with 4500 with HDMI cable. It means the PC sends each frame every 1/60s. Each frame is 24-bit, which means each frame consists of 24 1-bit pattern.

2. During each 1/60s VSYNC interval, there are only 24 1-bit patterns sent from the PC HDMI port. (8R 8G 8B,  and there is no requirement for the R bits to actually coorspond to red or for the bits to be displayed in order).

3. I want to display the 24 1-bit patterns for 3 times repeatedly during the 1/60s VSYNC interval. In other words i want each 1-bit pattern to be displayed for 1/(60*24*3) times.

My method was to set the pattern exposure time to be 1/(60*24*3) = 231.48 us and set the pattern sequence to be:

F0:R0 F0:R1 F0:R2 F0:R3 F0:R4 F0:R5 F0:R6 F0:R7 F0:G0 F0:G1 F0:G2 F0:G3 F0:G4 F0:G5 F0:G6 F0:G7 F0:B0 F0:B1 F0:B2 F0:B3 F0:B4 F0:B5 F0:B6 F0:B7 F0:R0 F0:R1 F0:R2 F0:R3 F0:R4 F0:R5 F0:R6 F0:R7 F0:G0 F0:G1 F0:G2 F0:G3 F0:G4 F0:G5 F0:G6 F0:G7 F0:B0 F0:B1 F0:B2 F0:B3 F0:B4 F0:B5 F0:B6 F0:B7 F0:R0 F0:R1 F0:R2 F0:R3 F0:R4 F0:R5 F0:R6 F0:R7 F0:G0 F0:G1 F0:G2 F0:G3 F0:G4 F0:G5 F0:G6 F0:G7 F0:B0 F0:B1 F0:B2 F0:B3 F0:B4 F0:B5 F0:B6 F0:B7

Is my method correct in your opinion?

I have attached the screenshot. Sorry that some part of my pattern sequence is not shown because the pattern sequence is too long.

Hello Song,

At a high level I agree with everything you said. Unfortunately I see two issues with this specific implementation. When doing external RGP Input Patterns (ie. an HDMI input) you are limited to a 2880 Hz binary rate. 1/2880 ~= 348us. Therefore, your minimum exposure time needs to be 348us instead of 231us. See Table 7 in the DLPC350 datasheet for more information on this.

The other issue is all the patterns in your sequence should be be displayed in 1/60 = 16666us. Therefore, with a 348us exposure time you can only display 16666/348 = 47 binary patterns before the next VSNC from the video data arrives. To fix this you need to find a way to reduce the input framerate or rethink your pattern sequence. For example. you could just show 24 of the patterns per frame. While it may be theoretically possible to have a sequence expand over multiple VSYNCs this is not reccommended. 

In my experience it's usually difficult to use a normal Windows computer as an input due to Windows formatting of video and other restrictions. A special program and/or hardware may need to be utilized. Alternatively, it is very poplar to use the internal flash for patterns which is less difficult. If you have a specific application you are trying to meet that makes this difficult please let me know.

Thanks,

Kyle

Hi Kyle:

Wow, impressive comment and sharp observation! I don't have a specific application yet.

The internal flash seems only capable of storing 48 patterns but I want to continuously stream data bits into the projector.

I noticed that the 2880HZ is the "external RGB input pattern rate". I am wondering whether this rate means the HDMI maximum data streaming rate or the DLP display rate. I am actually only streaming in 24-bit color images at a 60hz refresh frequency, hence my streaming data rate is only 60*24=1440 (1-bit pane) 

I am merely tripling the displaying rate but with the same content. Hence am I right to say that the 2880hz is sufficient to support my imagined scenario? I can carry out experiments on it with my 4500evm though.

If it is not fast enough to support my imagined scenario, is there another TI reference design with optics installed that I can purchase instead? thanks

Hi Kyle:

I am just streaming 24 1-bit planes per frame ( 60*24=1440 rate) but at the same time I am repeating each 24 bit plane three times on the projector end.

It is so sad that the 2880hz is the maximum display rate. Isn't DLP technology capable of switching micro-mirrors at an extremely fast rate? I will test my 4500 in the next couple of days to confirm its maximum rate and update you on this.

 

1. Are there other DLP EVM models that is capable of displaying faster which I can purchase? It has best be a model with optical components already installed.

2.  If I "extend across multiple video frames (i.e. can span across the VSYNC boundaries), wouldn't a portion of pictures not be displayed at all? Because the display rate cannot catch up with the incoming new data rate.  Input rate > output rate?

 

thanks so much for the help!

Song