How a digital to analog converter works

[variable]

can someone please explain how a digital to analog converter works if say your equipment includes a computer with a software like Labview, a Lab-NB board, a terminal block (USB) and an oscilloscope. what is each component doing and what is being transferred between them? thanks.

 

[berkeman]

Do you understand how a DAC works? If not, here's a tutorial on the R-2R DAC (as opposed to a binary-weighted DAC, which has some limitations):

http://www.allaboutcircuits.com/vol_4/chpt_13/3.html

National Instruments also has some good tutorials and articles about their boards. Check out this jump-off site:

http://zone.ni.com/zone/jsp/zone.jsp

Basically, to answer your question, the software on the PC writes to the DAC card to tell it what binary data it should convert into an analog voltage. The data transfers can happen in several different ways, but the simplest way to think about it is that the PC program writes a new data value to the card at each clock tick (whichever clock), and the DAC card drives the analog value for that data out at each clock tick. The PC software could write values out that made a sine wave at the analog output, for example. The DAC card typically has configuration registers that set whether the digital data represents a single-ended output voltage range (like 0V to 10V) or a bipolar range (like -5V to 5V).

The terminal block that is connected to the DAC card's output cable just makes it easier to probe the signals with an oscilloscope. In real applications of the DAC card, the cable connects to whatever circuit you want to drive the output analog waveforms into (like a speaker, or whatever).

Hope that helps. -Mike-

 

[variable]

thanks, that really helps. just one follow-up question. does the board have the same function as the card? I've been trying to look through the manual for the board and it's several hundred pages long so haven't been too successful.

 

[berkeman]

thanks, that really helps. just one follow-up question. does the board have the same function as the card? I've been trying to look through the manual for the board and it's several hundred pages long so haven't been too successful.

Sorry, I read your question fast and assumed that you were using an NI DAC card (like one that plugs into the PCI bus in a PC). Is the Lab-NB board an external DAC module or something? I tried searching NI.com for Lab-NB but got no hits, so it's probably from some other DAC supplier? Does it use USB or GPIB or some other interface to the PC?

If the Lab-NB is the DAC module, then yes, what I said in reference to an internal DAC card in the PC applies similarly to an external module connected to the PC via some digital interface cable.

 

[variable]

It's connected to the terminal block which uses USB and it's external. I think they are the same because I remember reading something about registers in the manual and the bipolar range, etc. Thank you so much for your help!