If you want to make an OSHW oscilloscope you should consider these boards... They are more expensive than a $20 one because of the PCB itself... ( I'm working on a 386 processor in Verilog/VHDL, and then a cross-assembler FPGA to convert x86 to ARM... So I wouldn't even start this project yet, so this is an interesting idea I thought of for the future)...
This is MUCH MUCH faster than the raspberry pi which the clock speed of the pi is very deceiving... This is also COMPLETELY OPEN SOURCE:
http://beagleboard.org/boneThe BeagleBone uses a TI AM3358 ARM Cortex-A8-based microprocessor. Announced on Oct 31, 2011, the main processor is available for as little as $5, uses a 0.8mm ball-grid array and standard DDR2 memory, making this board easier to clone than other BeagleBoard designs.
I also have some M/F jumper wire going to my DE-0 so I have programmable logic as well. 3.3v compatible and cheap...
http://www.altera.com/education/univ/materials/boards/de0-nano/unv-de0-nano-board.htmlThis is like the Xilinx Spartan-6 series but cheaper... This particular model is 22k LUT-4 I believe and the FPGA itself is around $10-20 ( maybe less now ) ... That's quite a lot of gates. I never started this project in 2004 because back then you only had maybe 6-10k LUT ( For reference a lookup table is sram cells I believe + 4-6 MUX or multiplexers... You can emulate basically anything, the hard-IP block DSP is also fairly good )...
I think if you were to make an OSHW oscilloscope you could get it into the $50-100 range in total with a custom PCB. The real work is just making the ADC front end since you might need to blow around $20-50 of prototype money selecting one with the right sample rate while keeping the cost low... That sounds like a joke but you could easily do it to those who are critical... If you have the I/O with serdes/transceivers in PLL arrays I'm sure a 400-700mhz A8 is enough ( not to mention it blows the doors off of the pi in processing power and I/O )... Once again this is only prototype cost to DESIGN an oscilloscope kit ( with another kit )... You're easily going to have to make a separate board since you don't know what voltage/current scenario you're going to get out of your front end even buying these two things... I think it's an interesting idea though... Then you can just feed it back to either the beaglebone or FPGA board... Analog devices also makes a $150 board that has a spartan 6 + blackshark on it @ 600mhz+ ...Which those are both budget lines that can be scaled up or down depending on needs. All you'd need as the hobbyist to solder BGA would be a cheap IR... OR even just the ATTEN hot air, reballing stencil, gel, etc... That sounds extremely fussy and risky, but I think if people had the technique down ( I've seen a lot of attempts to teach it on this site so I think it's the best place to talk about it) it wouldn't be that risky to try at least since the investment wouldn't be that high ( once the community has a premade PCB and the parts are standard for the kit )... The only real investment is getting together a kit based on these parts. But we'd have to prototype the system first, and THEN build an OSHW board specifically for test gear...
All the processing power is easy to get and an LCD display isn't that surprising to add... Even an 800x600 display is laughable for a cyclone IV FPGA since it can handle an overlay too... I'm not sure about the cost of that though... It would be fine even with monochrome I think. But once again it could be MODULAR and hardware-agnostic with risers... MUCH MUCH better than the weak amtel in the arduino, and it's a huge improvement over the pi... But the raspberry pi is also a $35 kit and it's ultra low cost. Beaglebone is around $90 but the processor itself is only $5... These particular FPGA and microcontroller are perfect I think for a test piece. I saw examples on the texas instrument site showing how to design your own washing machine ( commercially ) and everything with block diagrams... Which basically is a cry for help saying it's so cheap and fast it can be, and should be tried in anything almost... Xilinx has low-cost platforms, but they start out at $150 usually through digilent design, or they have no features like easy-access GPIO... I have also looked at analog devices blackshark boards ( which surprisingly is only $50 or so for one, but they only work with the BEmicro board, which also doesn't have the 40+ GPIO pins like the DE-0 by terasic )...
Anyways, I hope that offers some insight...
This is a rather tricky thing to find on google:
http://www.analog.com/en/evaluation/sdp-bemicro/eb.htmlThe SDP platform starts at $50 and goes up to around $175 I think? But this isn't easy to find on the analog devices website... Look at the H1 series...
http://www.analog.com/en/system-demonstration-platform/evaluation/index.htmlThe only problem with the $50 one is getting the connector to mate with your board. The cost of the nicer ones is for I/O, bigger PCB, and then the final one you're paying for the FPGA too...
http://www.analog.com/en/system-demonstration-platform/controller-boards/evaluation/EVAL-SDP-H1/eb.html ...They are almost a waste though compared to the beaglebone I think...