Low cost 32-channel standalone board

d

How late?

32000 bytes (1 second later) 1920000 bytes (1 minute later) 115200000 bytes (1 hour later) or 2764800000 bytes (1 day later)

Since the user didn't specify that he needed just 8-bit data, and

16-bit ADCs with appropriate sample rates are not too expensive, you might want to double the number of bytes per unit of time.

I've been doing preliminary design work for a system based on the AD7606, which simultaneously samples 8 channels at 16-bit resolution. Four of those on a fairly fast SPI port and an SD card and USB port should make an interesting project. Building even a few boards like that for $150 would be possible only if I amortized the design effort over many hundreds of boards and ordered the expensive parts in hundreds.

Mark Borgerson

How about a 32 channel sample-n-hold circuit with an external ADC ?

32-S/H circuits and a 32 channel mux should be less than $50.

The ADC will need to be fairly fast and the mux will need to be fast as well.

A parts cost of $150 should be close.

hamilton

And the required resolution and upper bound for the sampling rate is missing. For 24 bits you have to multiply your values by 3. And sampling really concurrently (I guess he means sampling parallel), means there is no mux and slight delay between the input samples allowed. This makes it much more expensive for good ADCs.

Parts cost for using some muxes, a good 24 bit ADC and a microcontroller with a SD-Card and USB connection could be below $50.

--
Frank Buss, http://www.frank-buss.de
piano and more: http://www.youtube.com/user/frankbuss

The real cost of this system will be a low noise PCB.

hamilton

Depends on the required resolution. 8 Bit should be no problem.

BTW: With the parameteric search at Digikey I found a nice microcontroller from Freescale:

Ok, looks like you can't buy it, because it is too new, but maybe this would be a one-chip solution for less than $10: It has 33 ADCs with 16 bit and a sampling rate of up to 8 MHz, and integrated USB.

--
Frank Buss, http://www.frank-buss.de
piano and more: http://www.youtube.com/user/frankbuss

Nice chip, but it looks like it has 2xADC with 16x multiplex each. The original question was:

If this just means sampling all the channels within 1ms, then the above chip (or similar) may be an option. Carefully study specs on conversion time, channel switching and settling times.

If the request was for real simultanious sampling of the 32 channels at >=

1kHz rate, then he would need something else. (maybe adding the sample and hold circuits, as mentioned earlier, would do the trick).

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

The scum also rises.
		-- Dr. Hunter S. Thompson

$150 / 32 ~= $4.69

At about $5 per channel budget, 12-bits and a 1K sample rate,

come in at $2.43 for 32 channels = $77.76 for just the 12-bit ADC parts.

A 16-bit version in a 12-WFDFN is the same price !!

This part uses an I2C interface, so any type of micro could be used to retrieve the conversions.

I wonder if 32 S/H circuits and muxs and 12-bit ADC would be much cheaper ?

hamilton

Designing a practical data acqusition device requires serious hardware and software effort and a development budget in 5..6 digit numbers.

If the goal is making a useful instrument just for yourself, then take a PC and add a data acqusition board from NI to it. It is not going to be any less expensive then that.

If the goal is doing something barely working for the sake of doing, then take an evaluation board for a USB-capable microcontroller with the built-in ADC, and add a breadboard with the 32-channel input multiplexer. With the sample rate as low as ~1kHz per channel, the 32 channels could be sampled in a round robbin manner.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant