Stick this to the wall

The 40 pins

The GPIO header of every Raspberry Pi from the B+ onwards. You will reach for this every single session from twenty-eight to thirty-six, and so will he.

5V power3.3V powerGroundGPIO — yours to use

3V3	1	2	5V
GPIO2 · SDA	3	4	5V
GPIO3 · SCL	5	6	GND
GPIO4	7	8	GPIO14 · TXD
GND	9	10	GPIO15 · RXD
GPIO17	11	12	GPIO18 · PWM
GPIO27	13	14	GND
GPIO22	15	16	GPIO23
3V3	17	18	GPIO24
GPIO10 · MOSI	19	20	GND
GPIO9 · MISO	21	22	GPIO25
GPIO11 · SCLK	23	24	GPIO8 · CE0
GND	25	26	GPIO7 · CE1
GPIO0 · ID_SD	27	28	GPIO1 · ID_SC
GPIO5	29	30	GND
GPIO6	31	32	GPIO12 · PWM
GPIO13 · PWM	33	34	GND
GPIO19	35	36	GPIO16
GPIO26	37	38	GPIO20
GND	39	40	GPIO21

Which way up? Hold the Pi with the USB ports facing you and the pins along the top edge. Pin 1 is then the top-left pin — the one nearest the SD card corner. Odd numbers run down the left column, even numbers down the right. Getting this backwards is the single most common wiring mistake, and the reason the ribbon breakout is worth buying.

Two rules before any wire goes in. Never connect a GPIO pin straight to 5V — the pins are 3.3V and 5V will kill them. And always put a resistor (330 Ω is fine) in series with an LED, or the LED gets one bright, final moment.

The GPIO pinout · sessions 28–36krishpi.sreeb.dev