LM741 based 4-bit DAC

Hi Folks,

As an attempt to understand R/2R DACs, I tried building a 4-bit DAC using an LM741. The circuit and the measured response are in the links below:

http://picasaweb.google.com/glman74/NutsAboutElectronics#5361295651529113874

http://picasaweb.google.com/glman74/NutsAboutElectronics#5361295658833572610

My 9V battery was only giving 8.4 V. Is this why the Vout for the last point (1111) in error, since Vref is only 4.1 V?

I realize that 741 may not be the best choice for a DAC, but I am just experimenting, and am curious to find out if I can build a 10-bit DAC this way.

I'd appreciate any suggestions on improving this circuit.

Thanks

A better op amp would be one of the rail-to-rail variety. The 741 type won’t operate reliably when the input is close to one of the power supply extremes.

You probably want one of the Single Supply and/or Rail-to-Rail type.

Single Supply: ~ cost $1.00
http://focus.ti.com/lit/ds/symlink/tlc272.pdf

Single Supply - Rail-to-Rail: ~ cost $3.00

http://focus.ti.com/lit/ds/symlink/tlv2772.pdf

Thanks.

But I am not sure if these ICs are easily available here in Bangalore.

How about LM358? Is it a good choice for an R/2R DAC?

http://www.datasheetcatalog.org/datasheet/fairchild/LM358.pdf

My experience is that ‘rail-to-rail’ op-amps never really are unless you’re prepared to spend serious coin. It’s much better to spring for smoething like the MAX680 which takes 5VDC in and makes +/- 10VDC out for powering op-amps and the like. It costs ~$2.30 (plus the cost of four caps) and means you can use much cheaper op-amps.