Raspberry Pi Model B Schematics
raspberrypi.org
raspberrypi.org
I kind of wish there was a harder to use card edge connector for these - they could likely implement an additional 2 SD card slots or similar I/O.
I think it is great that they have released this - and I think that Broadcom also deserves credit for allowing them to release a schematic giving away the pin-out of the BCM2835 SoC - it makes the Raspberry Pi so much more useful to know what the outputs of the system are.
This opens up the possibility of trying to work out how to use the unused pins on the BCM2835 based on the names. I haven't been able to work out what the HD pin group does (probably not SATA or PATA based on the number of pins, and HDMI has its own pin group). There seems to be a CAM0 not connected to anything - given CAM1 seems to be a camera, it looks like it is for an additional camera. It also has CCP2 outputs for a CCP2 camera. I also haven't been able to work out what SLIM is - but given it has two pins, CLK and DAT, I guess it is some kind of serial data protocol.
If you're trying to duplicate the RPi exactly, you won't be able to. Nobody else can get the BCM2835 chip except the RPi guys.
Coupled with that, it can be really hard to get low volumes of some of the parts they use, like the SoC, PMIC (power management IC) and so on (although you can get free samples if you ask sometimes - but they generally won't give them to you unless there's a chance you'll put through a big order with them in the future). And soldering the BGA parts onto the board would be a pain unless you pay for it to be assembled for you...
Unless you know a lot about that sort of thing, it would probably be more successful to design something that interfaces with a Pi.
It was a great way of bridging the abstraction gap between the physical hardware and the code we typed at the keyboard. (We were also required to take courses in basic digital and analogue design and compiler construction to give an overview the rest of the stack, too.)
Nowadays, I think they've switched to using ARM boards for the second course in the build-a-computer series. From a hardware reliability and cost perspective it makes sense, but it's a little sad that the "I built one like this! Just not quite so neatly..." factor has been lost.
As a software guy, the details of the Pi's PCB layout are about as impenetrable to me as the internals of the SoC itself are. It's Magic Electronic Stuff!, but just a tad more powerful than the Z80 I used to play with.
Cheaper than the RaspberryPi? extremely hard. While a body more experienced than the RaspberryPi with more manufacturing clout can probably do that, the RaspberryPi foundation is a non-profit. Roku/Apple might be able to build a RaspberryPi for 75% the price, but their own profit would make it more expensive.
There are equivalently-or-better specced stuff on the market (Roku boxes that run Linux that can occasionally be found for $50, Apple TV that can occasionally be found for $80). But nothing at the $25/$35 price point with similar specs - and I don't expect any in the near future.
As for equivalents: It's a 6 layer PCB, with BGA and other SM components. That's really hard to do at home. So you're unlikely to see hobbyist rip-offs anytime soon.
At some point there might be another similar device - mass made in China, more power, more ram, but probably much worse documentation. There's certainly a big market for tiny dirt cheap computers.