Now my project using 908QY4 device for low power application, and use two 1.5V AAA batterys for power supply,I want to use 908QY4 AD for sample and monitor the voltage,for example, when the power is below 2.7v ,the alarm will turn on.
Could you please tell me if this is doable and how to achieve this aim?thanks.
You need a reference, normally the supply voltage is your reference. If your supply voltage varies then you need an independant reference. If you put a fixed reference voltage onto the ADC input you should be able to work this backwards from normal. As the supply voltage drops the reference voltage will appear to rise (or it actually will with reference to the supply). This way you should be able to implement a "fuel gauge" as well as a low alarm. This will come at the expense of the current required to run the voltage reference.