I am trying to get the arduino to sense when the max756 LBO goes to ground. My question is what is LBO voltage supposed to be before the low battery condition is met and what is the minimum voltage requires for the arduino to read high on the digital pins. I get a reading of less than 50mv using the dmm when testing LBO and this seems quite low to me.
Its an open drain output, you need to enable the internal pull-up on the relevant Arduino pin.
How do I go about doing that? and what exactly does that mean?
An open drain output will sink currentwhen active, so with pullups it will read high, then when it gets activated it will go low
You can think of an Open Drain output as a switch, rather than a digital signal.
Normally when outputting a value, an output either outputs (say) +5V, or connects to ground.
With Open Drain the +5V part is missing, to be provided by you. In the normal "off" state the switch is off. If you have a resistor connected between the output and +5v (could be the internal "pull up" resistor in the Arduino's input), then the voltage at the output will be +5V. When the output switches on, the switch is activated, and the output is connected to ground. This makes the voltage at the output 0V. So the output is basically the inverse of the actual function (known as "Active Low").
You can turn on the internal pull-up resistor of an Arduino input port by writing a HIGH to the digital input.
pinMode(4,INPUT); // Set the pin to be input
digitalWrite(4,HIGH); // Enable the pull-up resistor
value = digitalRead(4); // Get the input value