From spec sheet:
Supply voltage: 2.5 V to 5.5 V
You are providing the voltage of 6 AA batteries, around 9V. So it is too high. If you have a 3-AA battery pack, it will work. Or if you connect the power to arduino 5V directly.
I cannot believe I forgot about that - thanks for reminding me!
No common GND connection?
Did not catch that.
So OP, why do you want to power this sensor with a separate battery from arduino?
I knew it was a bad idea to not tell you guys the whole story.
Okay, so I have some circuit boards. Here's the schematic for how they're supposed to work. The plan is, there are 3 PCBs, each with 3 sensors and an LED. (Yes, it is ok to use 3 sensors.) The LEDs draw about 98 mA, each, with the 51 ohm resistor they recommend. I can't use the Arduino to power them because it is already going to provide power to, let's see here: A 16x2 character LCD, an XBee, an Adafruit Wave Shield, possibly a small amp, and a PCF8574 I2C port expander. (I'm not even sure if it can handle all of that, yet.)
The 3 PCBs will be wired together like this. ("To tagger" refers to the uC.)
The problem is, everything on the PCB (the 3 sensors and the LED) need to be powered by the same source. The PCB has 4 spaces to solder wires in, shown in the schematic - +5v, ground, data, and hit LED.
My new idea is:
+5v and ground will be taken care of by the battery pack.
Hit LED is simple - just tie it to ground, and trigger it with a MOSFET.
Now the data pin...here is where I'm stuck.
I have a schematic of my idea here. What I need is: on the schematic, there is a part labeled "???". I don't know if this kind of part exists, but I'll ask anyway. What I kinda need is a reverse MOSFET - where power can flow freely between drain and source, but while power is flowing, the gate pin outputs a 1. When power is not flowing, it outputs a 0. I imagine something like this would need to be powered as well.
What I'm asking is - does something like this exist?
(By the way - none of this matters if I can just use the data pin with the Arduino, without a common ground. I can't do that, right?)