Ah yeah I may have made a poor assumption in thinking it would work given it works directly from Spark and Arduino. I figured the Shield Shield would be able to drive at least the same current. Oops.
There’s a chip on the board that I’m not sure what it does (I could probably figure it out by taking one of mine apart):
But since I’m not supplying the PST2 with power, so I doubt that chip is really doing much (I highly doubt it’s a driver). So yeah, god point.
Seems like using a transistor is the better route to go, but curious with the pullup - if I add in a pullup resistor that just means it’s going to pull up the voltage when the output pin is low and higher when high? That means I might need to pick a resistor value that would be able to pull it high enough to engage the relay but keep it low enough to disengage?
Unfortunately, since I want to use I2C, 1-Wire, and relays, the Shield may not be my best choice. But I was planning on making a purpose built board with all this stuff integrated anyway. A little concerned I might run into the same problem as the Shield with converting the logic inputs. I was going to use MOSFETs for that since I really only need be concerned with I2C for my application. I was likely going to leave the signalling for the Dallas Temps to 3.3V (though maybe supply 5V to them). I’d like to do 5V signaling since I’m using the sensors on the end of cables (for underwater application) though the distance is 3 meters or so. 3.3V seems to work fine when using the temp sensor on Spark + breadboard so that may be ok.