When you need more inputs/outputs for your Arduino project, the response in some forums is "Use a MEGA" instead. While the Arduino MEGA does have more built-in GPIO pins (70 digital input/output pins ...

The internal transistor packs of ULN2803 act as inverters. When point A=0 and B=1, output pins 17 and 18 will be high ... Connect a 9V PP3 battery for power supply to the circuit. You can use ...