I want to make a simple water level indicator with tank full alarm as shown in the diagram. What I want to achieve is, when the tank is full to 100% and water is still flowing through the inlet pipe (ie, the pump is on) the buzzer should beep. I have two outputs from IC ULN2003 for that- Pin 14 switches on when the water level is 100% and pin 15 switches on when water is flowing through the pipe. Also, I want the buzzer to stay off as long as the above-mentioned conditions are not met. Now my questions are,
1) Is the circuit right on the transistor switch side? If not, is there any other circuit (preferably simple) which I can use?
2) Is transistor 3906 good enough for this use?
3) The resistor values, are they okay?
4) Should I give a reverse bias resistor to the transistor base as shown in the the second diagram (R2)?