I want to connect scanner for exampe Epson Perfection V33 to arduino throught USB, I understand that need to use USB host shield, but not understand how to send commands to the scanner.
My goal is scanner have to scan paper and save image to SD card, so question - how can arduino do it?
The first step would be to figure out the protocol used by the scanner you have. Most are not published because the scanner usually only talks to the driver provided by the scanner vendor.
Assuming it would succeed then a normal scanner would have scanlines of ~8inch x 600 dpi x 3 colors = 7200 bytes per scanline.
That is almost 4 times the total RAM of an UNO. So even at BW at 200 dpi you would have a RAM overflow in no time.
Unless your goal is different.... ????
You would have more chance of hacking into the linear CCD imager data lines and using arduino to control the stepper to move the image sensor
ok yes spi ram exist's but are you going to have enough speed to deal with a camera in its real time while also streaming that data to an external source without running out of memory on the MCU?
SPI ram is not ram that you plug in and it add's onto the arduino's internal memory, its more or less a tiny SD card
At risk of repeating myself you could try hacking straight into the linear CCD bus, ones i have used output serial data and are clocked by the host mcu so you control the speed of scan but others are different and it would be easy to drive the stepper, have a look here, this isn't my site but just one i found https://github.com/chiva/Arduino-CCD-TSL214