Types of signals being sent through different types of cameras

Question

I'm very much a beginner in electronics, so I apologize if the concepts I'm trying to understand are very basic. I've been looking into making a simple camera setup with my Arduino and an Adafruit product linked here. From looking at this article, It seems that for a simple setup to work, this would require connecting to a Raspberry Pi at least, due to its requirement for a camera module:

The Raspberry Pi camera board transfers data through an extremely fast camera serial interface (CSI-2) bus directly to the system-on-chip (SoC) processor. It does this through a 15-pin ribbon cable, also known as flexible flat cable (FFC), and connects to the surface mount ZIF 15 socket in the Raspberry Pi board. As you may noted, the camera module on this official Raspberry Pi camera board is identical to the camera modules (ccd imagers) found in many mobile phones.

I'm having trouble understanding this as a concept for a couple reasons.

1. Why does a camera, which presumably has a set amount of pins that give video output, require a camera module to "process" its data before sending it into the rpi?

   a. How is the raw input of a camera such as in the Adafruit product formatted?

   b. How is the "processed" input of the camera board formatted?

2. (more dumb question) Assuming there's around 1920x1080 pixels for a video that the camera can take, how is this compressed into the <20 number of pinouts that comes out of the cable?

3. As I understand it from my limited experience with circuit diagramming, the little markers are inputs and triangles are ground, but what are the rest signifying (do lines like CAM1_DN0 signify inputs?

4. How could a circuit be designed to read in pixels of a camera and do high-level processing?

Again, apologies if these questions are really basic, but I couldn't seem to find any way of understanding this in a very detailed format online. Any help would be appreciated. Thanks for reading!

Answer 1

Why does a camera, which presumably has a set amount of pins that give video output, require a camera module to "process" its data before sending it into the rpi?

The camera's output pins may use a different format, but in many cases, the camera module doesn't do any conversion. An example schematic shows the following onboard:

• Power supply (voltage regulators and decoupling)
• An oscillator to provide the necessary clock signal to the camera chip.
• An cryptoprocessor made available on the I2C bus of the board, as well as I2C level shifting.
• Common-mode chokes for noise suppression on the differential signal lines carrying video from the camera.

There is no intermediate conversion chip between the camera chip and the cable; the common-mode chokes are purely passive components that suppress certain types of noise on the line.

a. How is the raw input of a camera such as in the Adafruit product formatted?

There's no separate "raw input" in the example I found, the output of the camera IC directly conforms to the Camera Serial Interface. For a different module, you'd need to consult the datasheet of the camera IC to confirm the format.

b. How is the "processed" input of the camera board formatted?

It follows the Camera Serial Interface format.

Assuming there's around 1920x1080 pixels for a video that the camera can take, how is this compressed into the <20 number of pinouts that comes out of the cable?

The camera data is sent in a serial format over two differential lanes, with a clock signal alongside. The serial format means that bits of all the pixels in the frame follow one after the other. Per [this reference], "Each lane can run at up to 1Gbit/s (DDR, so the max link frequency is 500MHz)". As far as I can tell based on the abstract of the spec, there are multiple options for the image encoding, including 24-bit RAW.

As I understand it from my limited experience with circuit diagramming, the little markers are inputs and triangles are ground, but what are the rest signifying (do lines like CAM1_DN0 signify inputs?

Those lines are differential signals, they can be considered as outputs of the camera module. The SDA and SCL form an I2C bus, which is used to control and configure the camera, while the CAM1_Dxx pins carry the bulk video data.

How could a circuit be designed to read in pixels of a camera and do high-level processing?

It would need a differential transceiver that can handle the correct IO standard, speed, and encoding. If you're designing a chip you might pay for an IP core to integrate in your chip. If you're using an FPGA you will probably use a transceiver provided onboard the FPGA. An Arduino does not have the appropriate hardware to decode the high-speed video data.

Once you receive and decode the pixel data, you'd place it into a frame buffer and then do interesting stuff to it (e.g. encode it, stream it elsewhere, etc).

Being a member of the MIPI organization (which governs the spec) or otherwise having access to the spec is very helpful.