In SX Microcontrollers, SX/B Compiler and SX-Key Tool, alex41 wrote:

Hello,

I want my SX to produce an adjustable output voltage from 0-5v. The DAC is a LTC1257, 12 bit resolution. 

The problem I have is that the output is "choppy" to use a non-electrical term. 

My data connection to the chip works fine and my voltmeter is reading the voltage that the DAC chip should be putting out. The basic setup works just fine. Amperage output is very limited directly from the chip as it will only dimly light an LED. I've amplified the output of the DAC through a LM358AN amplifier. No problem lighting a LED now. Also the output is what it should be according to my voltmeter, but still the same choppy output. I'm using the Parallax USB oscilloscope to view the output.

I'm guessing that what I'm seeing is exactly what I'm supposed to see. I know the DAC turns on, creates a voltage, then turns off, repeating this many hundreds or thousands of times a second. I've tried a few capacitors on the output and it has helped, but I'm afraid if I use one that is too big, then it will create a delay when changing the output voltage.

Am I going about this all wrong? Web searches return lots of info on ADC's, but very little on DAC's. Even the datasheet on the DAC isn't very informative. It talks about noise filters, but I don't see this as noise from an external source.

Any ideas? direction to go? things to read?

Thanks for any input.

Alex

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