I guess the big question is: would 2 solenoids that share a ground fire off when only one pin is high? Both pins are output but only one is "on"."
pin1out(high)----solenoid--
pin2out(high)----solenoid--|
pin3out(low)-----solenoid--|---GND
pin4out(low)-----solenoid--|
pin5out(low)-----solenoid--/
Am I at risk of burning out anything?
Forget about driving the solenoids directly from arduino pins.
Don't do it.
I think the basic issue here is not so much a technical one as it is a communication problem.
I guess the big question is: would 2 solenoids that share a ground fire off when only one pin is high? Both pins are output but only one is "on"."
The obvious problem with above statement is that it indicates your lack of experience with electronics, which raises a red flag because who knows what ELSE you don't know ?
At no time should the solenoid be connected directly to GND, period.
WHY you ask ?
1-Because first of all they draw the maximum of an arduino output pin (40mA) so you can't use digital outputs to drive them.
2- Because they are inductive devices and should be driven using current SINK method and NOT current SOURCE (as you were planning)
3- They should be driven using transistors, mosfets or a mosfet based chip like the one Crossroads recommended.
4- When sinking current , the "-" lead of the solenoids does NOT connect to GND.
It connects to the DRAIN of a MOSFET or the COLLECTOR of a transistor. How the mosfet or transistor are driven from the arduino is another issue but the "+" lead of each solenoid should connect to the solenoid powers supply (which you probably don't even have or have even thought of)
5- The solenoids should NOT be driven by the power supply driving the arduino, only because it may induce inductive spikes on the logic power bus.
6- The GROUND BUS is another issue. The solenoid power supply "-" should connect to the GROUND BUS used by the mosfets or transistors. Your arduino needs to connect to that ground bus in order to turn those devices on but the connection from all the transistor or mosfets to the solenoid power supply ground should be direct and not through the "-" "line" as you are calling it (correct term is BUS. (another red flag))
Bottom line, the current path for the solenoids should be from the "+" BUS of the solenoid power supply to EACH solenoid OR to the solenoid "+" BUS , through the solenoid, then through the transistor to the emitter then to the solenoid GND BUS and back to the "-" lead of the solenoid p.s. , or in the case of mosfets , through the solenoid, through the DRAIN (of the N-CHANNEL MOSFET) , through the mosfet, then out the SOURCE of the mosfet to the solenoid GND BUS and back to the solenoid power supply "-" lead.
7- Each solenoid should have FLYBACK DIODE (AKA BYPASS DIODE)
just want to make sure I'm not doing something fundamentally wrong.
Everything you have suggested or implied so far is fundamentally wrong, starting with the idea of driving them from arduino pins to "sourcing " the current instead of "sinking" it (terms which I would be willing to bet are foreign to you) .
The first question of your post should have been:
"Where can I get a power supply to drive my solenoids ?" (ie: dc-dc converter)
SECOND QUESTION:
"How do I hook them up ?"
Google Search: "How to drive solenoid from Arduino"
The entire chip can source or sink 200mA.
The entire chip can source or sink 200mA.