I'm using this lithium backpack from Liquidware: http://www.liquidware.com/shop/show/MBP/Lithium+Backpack to power my Arduino Uno. The battery pack has a common ground with my Arduino and the AREF pin is also connected to that same ground.
The battery pack also has a 'status pin' which is directly connected to the positive terminal of the battery, and can be used to monitor battery life. This pin is connected to my analog pin 0. What I'm observing is that even though the battery pack is off (meaning no current will flow into the 5V input of the arduino, my arduino is seemingly drawing some power from the battery via the Analog pin 0.
This is resulting in my LCD backlight being faintly on, as well as the green 'on' LED lighting up as well. But, the arduino code is clearly not running, as the LCD displays nothing, unless I turn on the battery pack. This is a problem because even though the unit is 'off', it is drawing power from the status pin into the analog input and will drain the battery.
Is this to be expected? Does anyone have suggestions on how I might reroute things to achieve the stated interconnections, but without the battery drain problem?
The battery pack has a common ground with my Arduino and the AREF pin is also connected to that same ground.
Aref pin should never be grounded, it is normally left floating, unless one is using an external voltage reference in the +1 to +5vdc range.
This pin is connected to my analog pin 0. What I'm observing is that even though the battery pack is off (meaning no current will flow into the 5V input of the arduino, my arduino is seemingly drawing some power from the battery via the Analog pin 0.
Yes wiring a 'hot' signal to a otherwise unpowered chip will cause it to try and find a 'backdoor' circuit to ground causing lots of weird and undesired behaviour. In some case can even lead to chip damage. Either find a way to disconnect the 'hot' signal when the chip is powered off, or possibly place a series high ohm resistor from the voltage source to the analog input pin, you would have to experiment with how high a ohms you can use without effecting the accuracy of the measurement.
retrolefty, thank you for the information. Can I connect the aref pin to the arduino 5v pin which has the following states:
during normal battery operation, gets power from the battery pack voltage regulator
during charging, gets power from the external power source
Under both conditions I'd like to use the analog pin to measure the battery voltage and check battery life (or charging time). Under case 1, I sense a loop that might be undesirable. Note the battery is typically 2-4.5V and the backpack boosts the voltage up to 5V.
retrolefty, thank you for the information. Can I connect the aref pin to the arduino 5v pin which has the following states:
You should leave the Aref pin disconnected, the Arduino default analogRead() command uses the chip's Vcc power as the internal reference voltage. You have no need or reason to wire any external voltage to the Aref pin, unless you can specifically explain why you must.