Can the spark core get the amount of draw from the relay shield? EG, detect if a light is on or off?
Unfortunately no; measuring the current draw of high voltage electronics is somewhat complex, whereas simple relay controls are relatively simple. However Ladyada’s got a tutorial for hacking a Kill-a-watt to send power consumption via XBees, and I bet it wouldn’t be too hard to do something similar with the Spark Core:
@zach Thanks again for the info! I’ll check that out. I don’t think it’ll be critical, it just would have been a neat bonus.
@mnewport I designed another relay shield that can do that:
Using on of these:
You can also toggle the relay manually, and the Spark Core can know if the the relay was enabled manually or through the Spark Core.
I’ve tested the PCB with and Arduino and it works fine, but I have not a Spark Core yet so is not really tested with it.
You can order a PCB on OSHPark if you want to try it.