Raspberry Pi CSI Camera Module

The Raspberry Pi camera module transfers data through an extremely fast Camera Serial Interface (CSI-2) bus directly to the Broadcom BCM2835 system-on-chip (SoC) processor. It does this through a 15-pin ribbon cable, also known as a flex cable, and connects to the surface mount ZIF 15 socket.

The two data lanes on the CSI-2 bus provide a theoretical 2 Gbps bandwidth, which approximates to around 5 MP resolution. Therefore, this is what I would expect the new cameras to have. It is very likely to have a maximum video recording resolution of 1920 pixels × 1080 pixels at around 30 frames per second. This is reasonable for the current technology that is around.

Compliant Camera

Mobile Phone Camera

I decided to have a look at some of the Mobile Industry Processor Interface (MIPI) compliant cameras that were already available in mobile phones. This meant making a trip to David’s mobile junk-shop emporium where he keeps all sorts of mobile phones.

After opening many phones, I managed to find a fixed focus lens camera module that had a chance of working. It had the OV5647 integrated circuit (IC), and after researching its design, it turned out to be a 5 MP (2592 pixels × 1944 pixels) camera with 1080p HD recording capability.

As you can see, the CCD imager on this mobile phone is similar to that on the official Raspberry Pi module.


Pinout

After trawling through databook manuals, I managed to find the pinout data for this camera IC. It was not only MIPI compliant but also CSI-2 compliant. I managed to find the complete manual for this chip, which includes information on how to interface the IC, pinout, and the timing control registers used to write an ideal driver. These standards have been in use for many years I suppose. The only problem was that the connector was different because mobile phones use a smaller connection, as space is limited. I therefore had to use a small PCB to solder the wires from the camera.

Module Size

As you can see, many cameras follow the MIPI standard. The principle of serialising CCD data is the same and there are only a few manufacturers of these chips. These camera modules can be very small; this one is smaller than a British penny.

Result

Result

Unfortunately, my recycled ribbon cable was just long enough to take this photograph of my hi-fi system behind my desk. On the other side were my whippersnappers all waiting patiently for their turn to take a photograph. As you can see everything was wrong with this photograph, including, lights, focusing, and composition.

Cost

An image sensor IC is usually inexpensive to manufacture and one could buy them for as little as a few pounds on eBay, however, there is the possibility that vendors and sellers may take advantage of this and a $4.00 camera might turn into a "Raspberry Compatible Camera" that costs significantly more. However, I anticipate that once manufacturers in China have the technical data for it, then they may flood the market, and costs would drop to as little as a couple of pounds per camera!


Conclusion

In conclusion, I would have to say that it was not worth spending so much time and effort to make my homemade camera. The experience of reverse engineering and hacking something was interesting though. For the software driver I had to guess many of the parameters from memory. I shall wait for the official camera to be released and see how it compares to my homemade DIY Camera.

This Article Continues...

Raspberry Pi CSI Camera Interface
Raspberry Pi CSI-2 Connector Specifications
Raspberry Pi CSI Interface Connector Pinout
Raspberry Pi CSI Camera Module