Your thoughts on design testing?
Just wonder what your thoughts and guidance are on the following:-
I have a battery powered microcontroller with analogue circuitry and an LCD in a plastic case. The product works and meets my design goals, but I decided to do some additional test and measurements with a portable digital scope for documentation purposes.
This causes problems I have not observed before (with mains powered earthed designs and test equipment).
1. The battery powered scope when connected to the circuit injects noise. This is made worse when charging/ operating via a mains powered supply with the power supply adding to the noise.
2. Adding a mains earth connection to 0V also makes the noise worse as does placing the unit above an earthed sheet.
Clearly the scope and probe are acting as an aerial injecting noise into the sensitive parts of the analogue circuit. The scope and its power source are also acting as noise sorces. Adding an earth to 0V makes matters worse, by providing a good ground.
In normal use the sensitive parts of the design are of small area on a ground plane and unaffected by the normal environment.
So what are good testing techniques for battery powered portable circuits?