Where can I buy a good ADC and DAC converter?

Question

I am looking for an ADC DAC that is easy to interface with a computer. USB or PCI interfaces are both good. I need to be able to respond to an analog signal comming in and have a feedback response within under 1ms (as fast as possible, but 1ms is a good start). Preferably something that is < $1000 too, most of what I have seen that can do this is > $3000. Any ideas? And I need 18 bit output resolution. Input resolution of 8 bit would be good enough.

LeftField, many sound cards have 24bit DACs so 18bit is certainly not unatainable.

The application is to position a mirror for an interferometer. The mirror moves due to thermal variations. The mirror is kept inside a vacuum chamber and also vibrates due to the vacuum pump.

Answer 1

A USB or PCI interface?? No!!!
You can do this MUCH easier and MUCH cheaper with a cheap micro. Look at www.atmel.com and their 8-bit AVRs, you can get a development kit for @$49 at Digikey and you should be able to do everything you want. 18 bit output resolution is pushing it in any circuit, you need to ask yourself what you are looking to gain (resolution or accuracy) The AVRs have 10-bit ADCs on them, and can develop a DAC from a PWM with up to 16bit (or more) resolution. If you want a better ADC or DAC, look at integrating a device from Linear Devices (www.linear.com) or Analog Devices (www.analog.com). You can probably get your chip, power it from USB, connect it all with a a serial port (USB->RS232 convertor IC from www.ftdichip.com) on a solderless breadboard for under $50. ($20 USB/RS232, $8 AVR, $15 breadboard, $7 ADC). Simple. And you control your own destiny..
Check out www.avrfreaks.net for more info on AVRs. They are super easy to use

Answer 2

Well if it isn't extreme, technically, than it may be a bit optimistic price-wise;. From the literature and sources I have, you won't get a plug-and-play card with 18 bit output resolution for < $1000.--.
I also don't understand why, considering that you can get a chip set for an ADC 18 bit serial output like the MAXIM 132 for only $8.-- and a DAC chip is about $4.-- ....
If you would consider building something from a chip set level, them MAXIM is likely the source with the most specifications to choose from.
http://www.maxim-ic.com/ADCDACRef.cfm

Answer 3

18 bits of output resolution sounds a bit extreme.

Answer 4

There are many on-line services supplying electronic components - Arrow Electronics, Digi-Key, Future Electronics, RS-Catalogue... I know for sure that Digi-Key can do this becasue I use their service (www.digikey.com).