I'm designing a circuit that will use a combination of switches and resistors to allow a microcontroller to identify which switch was pressed based on the voltage read and perform a switch-specific action. The design that I've come up with involves using a transistor to activate a relay, which powers the microcontroller. When the microcontroller is powered, it pulls a pin high to take over powering the relay. When the action is finished the microcontroller pulls the pin low, deactivating the relay and cutting power to the microcontroller.
I've tested the circuit with one switch and a voltage divider to simulate the largest resistor/lowest voltage combination from my switch array. The voltage that I've calculated at the transistor is 1.6 V, and the current is 0.017 mA. The high resistor values are necessary since I need approximately 0.2 V differential between switches. The problem is that the transistor is not being activated (it works if I feed it 5V directly).
My question: Is this because the current is too low? How would I go about rectifying this (other than decreasing resistances)? If there is a better approach to this problem, I'd love to hear it also.
The diagram omits the 15 other switches and resistors for simplicity sake.
This is a circuit for a picture frame that will do specific actions depending on the button that is pressed. This will be battery-operated using 6 D-cell batteries, mounted on the wall. I'd like to get months if not years of operation out of it before having to replace the unit. My Arduino with an attached shield (with using a MAX667 power supply rather than the stock one) consumes 45 mA at low power. The stock Arduino doesn't go into low power mode although with a programmer the chip can be modified to go into low power mode and consume nA of current. At 45 mA, the batteries will last about 11 days (266 hours for a 12000 mAh battery). Hence the requirement that the resistive ladder turn on the device.