Hi!
For a project I'm going to be using a Li-po battery for power.
To charge this battery, I'll be using the TP4056 chip with DW01x protection IC. (Got 2 for like $1 on ebay).
When I connect the micro-usb to the charging-circuit, a red light turns on if it's charging (a blue if fully charged). When the red light comes on, I want to put all the Arduino (and other IC's) to sleep, and wake up when the red light goes off.
Looking at the datasheet of the TP4056 and specifically at pin 7, it says it's an open drain that's pulled low when the light should be on.
(Pin7): Open Drain Charge Status Output: When the battery is being charged, the
pin is pulled low by an internal switch, otherwise pin is in high impedance state.
I know how to set up the interrupt to wake the Atmel chip on a pin state change.
But I'm not sure how to wire everything up to be able to read the state of pin 7 on the TP4056.
The schematic for the LED on the charging broad looks like in the attached image.
Thanks in advanced!
If V+ is lower than 5V then all you need to do is to connect pin 7 to an Arduino input to read it.
V+ would be the 5V+ from the micro-usb when plugged in. So when would be 5V+ even if it's not charging (Battery fully charged)
But if I where to desolder the LED, then the pin 7 of the TP4056 should act as ground when the light should be on. But should it also act as 5V+ when the light is off?
Or would it act as a resistor when the light is off and there for (in coupling with the external resistor) be a voltage divider?
Again, referring to the little information in the datasheet.
When the battery is being charged, the
pin is pulled low by an internal switch, otherwise pin is in high impedance state.
Or is that exactly what you mean? 
But if I where to desolder the LED, then the pin 7 of the TP4056 should act as ground when the light should be on. But should it also act as 5V+ when the light is off?
Yes BUT you need to keep the resistor in if you remove the LED. Do not connect pin 7 directly to 5V.