SCL SDA AREF GND 13 12 ~11 ~10 ~9 8 7 ~6 ~5 4 ~3 2 1 0 IOREF RESET 3.3V 5V GND GND VIN A0 A1 A2 A3 A4 A5 DIGITAL (PWM ~) POWER ANALOG IN UNO CH340G ATMEGA328P − − + + − − + + 1 1 5 5 10 10 15 15 20 20 25 25 30 30 j j i i h h g g f f e e d d c c b b a a CLK DT SW + GND KY-040 R1 · 220 Ω U2 · KY-040 U1 · Arduino UNO D1 · green U1 · Arduino UNO U2 · KY-040 R1 · 220 Ω D1 · green 2 2 3 3 4 4 5 5 7 7 9 9 11 11 13 13 14 14 15 15 16 16 17 17 18 18 b b d d f f g g h h j j MODEL · DC simulation USB 44.9 mA 0 A 0 A 0 A 4.99 V 4.99 V 4.99 V 4.99 V 0 V 0 V 4.99 V 4.99 V 4.99 V 4.99 V 0 V 0 V 0 V 0 V