Hi jackrae,
Thanks for the reply. In this instance, the implication you speak of is not as clear. We'd like the Arduino to make these measurements, and control two other shields that transmit this data wirelessly. Ultimately, the Arduino will be entirely powered by this transformerless power supply, similar to the Tweet-a-Watt.
For the prototyping though, we obviously would prefer having a permanent USB connection that we can upload the new code, and read some values from the computer. As I understand, this is when the safety issues arise, right?
So in essence, we should use the opto-coupler during the prototyping phase, but not once we get things running? Is this a fair assessment?
Also, out of curiosity, is there a way to have the analog sensor's ground be set independently of the power supply ground?
Thanks again!