Introduction: Idea: Medium Speed USB Oscilloscope.
Just an idea at the moment. A (cheapish) USB oscilloscope with moderate resolution at medium speeds.
TI has two high speed (2MSPS) 16 bit analog to digital converters (ADCs), the ADS8411 and ADS8412. One is differential, the other is single ended.
A PIC 18F2550 (with USB) can read the ADC and send data to a PC for display.
2 MHZ of speed isn't that great, but its faster than a multimeter :)
USB full speed is 12 Mbps
I guess I can sustain about 8Mbps of data through the USB, leaving 4 bits of control layer for every 8 bits of data.
At full ADC speed (2MSPS) samples would have to be limited to 4 bits resolution (and combined into a single byte?) to hit the 8Mpbs mark.
8 bit resolution = 1 million samples/s max (8mbps)
16 bit resolution = 500K SPS max (@ 8 mpbs throughput)
The ADS841x interfaces with some control lines and a 16 bit bus - a low instruction count can be used to move the value from the PORTS to the USB peripheral.
@ 48MHZ the pic does 12 million instructions/s.
@ 2 MSPS (or 2 MHZ acquisition speed, 4 bits resolution) there is a 6 instruction limit to move data from port to USB. This could be considered 12 instructions @ 4 bits because 6 instructions would just move 4 bits into a byte, other operations could be done during this time.