Grounding problem? Wave attenuates when I plug in USB.

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SUMMARY

The discussion centers on a PIC-based system experiencing signal attenuation when connecting a function generator to an ADC input while powered via USB. The issue arises when the grounds of the board, USB, and function generator are connected, resulting in a significant loss of signal integrity. Participants suggest that the circuit's layout and grounding scheme may be contributing factors to the problem, indicating a need for further clarification on the circuit design.

PREREQUISITES
  • Understanding of PIC microcontroller architecture
  • Knowledge of ADC (Analog-to-Digital Converter) functionality
  • Familiarity with USB power supply principles
  • Basic circuit design and grounding techniques
NEXT STEPS
  • Investigate grounding techniques in mixed-signal circuits
  • Learn about signal integrity and attenuation in ADC applications
  • Explore USB power management for embedded systems
  • Review circuit layout best practices for noise reduction
USEFUL FOR

Electronics engineers, embedded systems developers, and hobbyists working with PIC microcontrollers and ADCs who are troubleshooting signal integrity issues in their designs.

KingNothing
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Hi all. I have a nice little PIC-based system built onto a breadboard. It has ADC and USB capabilities. I wish to connect a function generator to one of the ADC input pins of the PIC to feed it a sine wave. The board is powered by the USB. However, whenever the three grounds are united (board ground, USB ground, function generator ground), the signal gets severely attenuated to where is it barely recognizable.

Can anyone help explain this?
 
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When you plug in the USB plug, the signal vanishes?

But the circuit is being supplied with power by the USB.

So, what is powering it before you plug in the USB?

Maybe you need to explain your circuit and layout a bit more.
 

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