Problem of communication of two devices having different baud rate..

[k_ishan]

hello......
i am doing project on "transmission of images from a robot to a computer or laptop".
i am using CMUcam for capturing images as it has serial USART interface capability...
CMUcam can transmit image data through USART with only 115200, 38400 and 9600 baud rates.
After capturing image i want to transmit this data by using RF tranciever module.
RF module i am using is also having USART interface. But RF module i am working with works with baud rates only less than 9600.
Thus i want to communicate a camera whose baud rate is greater than 9600 with a RF tranciever whose baud rate is less than 9600.
so please please suggest some solution to this problem......

 

[3v0]

you need to buffer the data from the camera then send it out at the lower baud rate.

 

[k_ishan]

you need to buffer the data from the camera then send it out at the lower baud rate.

can u please explain how to buffer data from camera?

 

[Sceadwian]

The simplest solution would be to use a micro controller to receive the data store it in memory and then when the full image had been received to transmit it over the RF link.

 

[ronsimpson]

The simplest solution would be to use a micro controller to receive the data store it in memory and then when the full image had been received to transmit it over the RF link.

Why full image?
The camera can transmit at 9600. The RF module can transmit at "less than 9600". I don't know what that means but lets say 4800.
If the data comes into the buffet at 9600 and exits the buffer at 4800 then only half of the image needs to be stored.

A quick search for "CMUcam" came up with many different versions with a wide range of baud rates. Down to 110 baud.

 

[ronsimpson]

From CMUcam4 manual:

The new baud rate can be any number between 1 BPS and 150,000 BPS inclusive. If the new baud rate setting is out of range it will be limited to be within 1 BPS and 150,000 BPS inclusive.

 

[chandan28]

using a controller to store image and then transmit at lower baud rate is not going to be that easy you need to consider other factors also
1. at what rate images are transmitted
2. size of image to be transmitted
3. how much data you can store in controller
4. and you need to change baud rate every time when sending and receiving data
consider all these cases before choosing controller

so better option would be use components which can operate in same baud rate

 

[k_ishan]

i am thinking of using ATMEGA128 as it has 128 kbytes of flash memory.
i think image data is of size upto 15-20kB..........

 

[k_ishan]

i am thinking of using ATMEGA128 as it has 128 kbytes of flash memory.
i think image data is of size upto 15-20kB..........

 

[k_ishan]

Why full image?
The camera can transmit at 9600. The RF module can transmit at "less than 9600". I don't know what that means but lets say 4800.
If the data comes into the buffet at 9600 and exits the buffer at 4800 then only half of the image needs to be stored.

A quick search for "CMUcam" came up with many different versions with a wide range of baud rates. Down to 110 baud.

yes by "less than 9600" i mean 4800.
but i think complete image should be stored in memory.
because for receiving i am using 9600 baud rate and for transmitting i have to use 4800 baud rate.......

so baud rate should be changed in between transmission and receiving.......

 

[ronsimpson]

i am thinking of using
as it has 128 kbytes of flash memory.
i think image data is of size upto 15-20kB..........

The image should not be stored in flash memory. 128kbytes. Flash is for the program.
The sram memory is for data. 2kbytes.

A 640x480 low resolution camera will have 300k pixels. A b/w 8 bit picture will need 300k bytes. A color RGB 8 bit picture is 900kbyters. There is a JPEG camera that compress the video first. Does your camera compress the video. Which CMUcam camera are you using?

 

[k_ishan]

From CMUcam4 manual:

The new baud rate can be any number between 1 BPS and 150,000 BPS inclusive. If the new baud rate setting is out of range it will be limited to be within 1 BPS and 150,000 BPS inclusive.

i am using CMUcam1.....

 

[k_ishan]

The image should not be stored in flash memory. 128kbytes. Flash is for the program.
The sram memory is for data. 2kbytes.

A 640x480 low resolution camera will have 300k pixels. A b/w 8 bit picture will need 300k bytes. A color RGB 8 bit picture is 900kbyters. There is a JPEG camera that compress the video first. Does your camera compress the video. Which CMUcam camera are you using?

i am using CMUcam1 whose resolution is 80x143.
herewith i am attaching a link which contains all the information about CMUcam1...
**broken link removed**

 

[ronsimpson]

I found the manual.
80x143=11440 pixels. 2 bytes/pixel 22.44kbytes in a picture. No compression. You need a 22.44kbyte buffer to hold the picture. The ATMEGA128 is too small.

 

[k_ishan]

I found the manual.
80x143=11440 pixels. 2 bytes/pixel 22.44kbytes in a picture. No compression. You need a 22.44kbyte buffer to hold the picture. The ATMEGA128 is too small.

can u please explain more about buffer circuits and buffer ic's.

 

[ronsimpson]

https://www.sparkfun.com/products/8773
This camera has compression. 160x120 (~ 3kbyte)

 

[k_ishan]

https://www.sparkfun.com/products/8773
This camera has compression. 160x120 (~ 3kbyte)

i dont have any option like buying another new camera.
i think i should use buffer....
bu i dont have any idea of using buffer....

 

[Sceadwian]

The Atmega128 supports an external memory interface, you can add plenty of memory to it.

k_ishan, you've been given plenty of ideas of how to use a buffer, it's not a complex thing, you store data and send it when you're able to.

 

[k_ishan]

thank u very much.....i'll surely try this.....

 

[ronsimpson]

Try searching for this:CMOS Camera Module OV7670 Display + FIFO AL422 / AL422B
The CMOS Camera Module OV7670 Display goes for about $10 on ebay and is a digital camera. 8 bit parallel data out. It can be slowed down.
The + FIFO AL422 / AL422B makes the price $30 but gives you a FIFO memory so the data can be retrieved at any speed.
The data is in parallel format and needs to be converted to serial for you radio. That part is easy.

VGA, 1/4VGA or 1/8VGA