ADC (analog to digital conversion)

[karmax]

hi,
   I want to make adc that we can interface with computer .I want to make adc whose sampling rate should be more than 250KS/s/ch and i need 4 channels and resolution should be 18 bits.Its least count should be 5uv.I want to use in place of DAQ (data acquisition card) for getting the data of my 4 hydrophones.please help me out

[Admin]

Impossible.

You'd be lucky to get more than about 3 KS/s/ch on a 16MHz microcontroller at a UART of 230400 kbps at 8 bits resolution. You'd also be very hard pressed to find any microcontroller with more than 12 bit ADC resolution.

That said, to hook it up to your PC:
250 KS/s/ch at 18 bits for 4 channels = 250000*(2^18)*4 bps = 262 Gbps

The maximum theoretical speed of USB 2 is about 480 Mbps - a thousand times slower.

That said, have fun with this until you buy a professional oscilloscope:
http://www.societyofrobots.com/sor_scope.shtml

[waltr]

hi,
   I want to make adc that we can interface with computer .I want to make adc whose sampling rate should be more than 250KS/s/ch and i need 4 channels and resolution should be 18 bits.Its least count should be 5uv.I want to use in place of DAQ (data acquisition card) for getting the data of my 4 hydrophones.please help me out

For those specs a commercial DAQ card would be the best way to go.
High speed, high resolution (>16bit) data acquisition is not trivial.

[nottoooily]

Why 2^18?? I'd have thought you only need 250000*18*4 = 18Mbps = pretty fast but not impossible.

250 KS/s/ch at 18 bits for 4 channels = 250000*(2^18)*4 bps = 262 Gbps

[Admin]

oops sorry, brain fart, nottoooily is correct . . . I was wrongly thinking of resolution of 2^18 was also the memory required to store it!

That being said, the Axon USB can only go up to 1 Mbps, and you probably won't find anything much faster. At least not until USB 3.0 becomes everyday, and that'll take a few more years . . .

[karmax]

oops sorry, brain fart, nottoooily is correct . . . I was wrongly thinking of resolution of 2^18 was also the memory required to store it!

That being said, the Axon USB can only go up to 1 Mbps, and you probably won't find anything much faster. At least not until USB 3.0 becomes everyday, and that'll take a few more years . . .

http://www.ni.com/dataacquisition/usb/ But if you see this link they have various usb DAQ that works in few MS/s/ch.and in 16 bit also.But the problem is that i want 18 bit resolution .May be 16 bit also work but i am not very sure so i dont want to buy it first .first i want to try with 16 bit and 18bit .

[hopslink]

The link you post also has 18 bit DAQ's. I would second waltr's suggestion. A DIY solution will almost certainly run to hundreds of $ and a considerable amount of work.