System with dsPIC which records video signal

[florinalex]

I want to build a system with a PIC (dsPIC) microcontroller that will capture images from a PAL video camera and write them to a SD memory card. I want to know if anyone built this or if it's possible. Thank you.

 

[Buriedcode]

Re: Record Video Signal

Hi,

My knowledge of analogue TV signals is sparse...but I know that you'll need a very fast ADC to capture a frame, a lot faster than the one in any dsPIC. With the highest frequency in PAL being around 5.5Mhz, you'll need to sample at 11MSps, minimum 8-bit. I'm just winging it here but doesn't PAL have a frame rate of 50? Interlaced...so 25 full frames persecond. Thats 40ms, at 11Msps = 440Kbytes of data. I guess a dsPIC could handle that, for storing it on an SD card (spi isn't it?)..but...at that sample rate...I don't think the dsPIC has enough speed. I 'think' they run at 40MIPS max... so assuming you read in a byte from each sample (in parallel) you'll have 4 instructions to store it, on the dsPIC or somewhere else.

I don't think that is going to happen without fast external ram, connected directly to the ADC. Of course, the dsPIC might be able to 'control' the process, that is, start a conversion when it detects a 'start of frame', and possibly use its PWM hardware to generate the necessary clocks for the ADC/RAM, because if I'm not mistaken, the PWM hardware on PIC's can go as fast as the instruction period, AND is in phase with it.

Then all you would do, is start to read back the data from the ram, storing it in the SD card, on the fly.

Google it! thers plenty of frame capture designs that use various chips, including a few that use pure logic (oh yes, hardcore electronics).

Failing that, an FPGA/CPLD could do that just fine, although it could format the SD card for storage, and you'd still need the fast ADC and ram.

As I said, I'm not expert, but thats how I would do it.

BuriedCode.

 

[alec82]

Re: Record Video Signal

hi Buriedcode
do you know micro or dsp that can do this?
best regards

 

[Buriedcode]

Re: Record Video Signal

Hi,
As I said, I'm no expert, I've never built/designed a frame grabber, or used one, I just replied because no-one else would.

I am not aware of any 'one-chip' solutions, let alone ones using a DSP or micro. The key to this is a very fast ADC, one designed for video (there are plenty about), some RAM, and a form of 'contorller' that controls the ADC and ram. You'll also need a way to detect the start of frames/line. There are 'sync seperator chips' around. Some seem to just out the vertical sync, other do the horizontal sync as well. As you can see, even for a basic frame grabber, we're up to quite a few chips already.

Try here for ideas:
http://www.epanorama.net/links/videochips.html
http://www.epanorama.net/links/videocircuits.html

Sync seperator chips.....to tell you when to start grabbing a frame.
**broken link removed**
http://www.intersil.com/cda/deviceinfo/0,1477,EL4581,0.html

Some reference designs:
http://www.atmel.com/dyn/resources/prod_documents/DOC0251.PDF
http://www.epanorama.net/links/videocircuits.html#digitalcircuit


Well, I'm out of my depth, I have a basic understanding of how these things work, but I have no reason to design one myself. Still, its interesting! And if people can make a 200MSps oscilloscope with a PIC micro (note: it uses MANY chips as well), who knows what else it can do

Good Luck,

BuriedCode.

 

[Drago]

Record Video Signal

I'm using mainly DSP. I have several TSM320C6711 and with a fast ADC they can handle the task. My experience with FPGA says that you can do this too. Take a look on Xilinx Spartan II/III series.