×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

AD974 output fluctuates

AD974 output fluctuates

AD974 output fluctuates

(OP)
I am using AD974 to convert analog voltage from an instrumentation amplifier and send the result to PIC microcontroller.  The output from AD974 fluctuates as much as 100mV.  I am providing clock from the PIC by just toggling a pin on a port.  My clock does not have 50% duty cycle.  I have also tied the WR1 and WR2 to ground to have the latch transparent since I want to use all four channels and don't want to toggle WR1 and WR2 all the time. Any idea why the ouput fluctuates?

RE: AD974 output fluctuates

Are your inputs connected to anything when you measure this, or have you put locally generated dummy input voltages to eliminate any external influence?

RE: AD974 output fluctuates

(OP)
I tried it even with a fixed voltage and also monitored the voltage with the multimeter.  It still fluctuates.

RE: AD974 output fluctuates

Does you circuit have adequate power supply decoupling? You should have, as a minimum a local decoupling cap on each IC of about 10 - 100nF, and bulk decoupling at the origin of the supply. If your PIC has large current pulses, add a 10uF electrolytic local to the IC.



----------------------------------

If we learn from our mistakes,
I'm getting a great education!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources