Teensy 4.1

Fig. 1. Teensy 4.1, 2x24 2.54 mm, 61 x 18 mm. Hover or tap a signal to light up every pin that carries it.

• No pin is 5 V tolerant. Not one, including the ones that share a name with a 5 V peripheral. A 5 V sensor output into any of these is a damaged board, so level shift or divide first. This is the single most common way a Teensy dies.
• Vin takes 3.6 to 5.5 V. The on-board regulator will hand back 250 mA at 3.3 V, and that is the budget for everything you hang off it.
• This diagram is the two 24-pin edge rows, which is what a header solders into. Pins 42 to 54 exist too: 42 to 47 are the SD card socket signals, and 48 to 54 are pads on the underside. Several of those are printed twice on PJRC's card because the same signal reaches two places.
• Also on the underside: VBAT for a coin cell that keeps the real-time clock running, pads for the Program and On/Off buttons, a 6-pin Ethernet connection, and footprints for extra flash and PSRAM.
• Pin 13 is the on-board LED as well as SPI SCK. Using hardware SPI makes the LED flicker with traffic, which is a free bus activity indicator and a nuisance in equal measure.
• Every digital pin can raise an interrupt, which is unusual and worth remembering before you go hunting for the special ones.
• Analog pins A0 to A17 are scattered: A0 to A9 sit on the right row around pins 14 to 23, A10 to A13 are on the left among 24 to 27, and A14 to A17 come back on the right at 38 to 41.
• The USB connector is at the top of this diagram. Turn the board over and the left column becomes the right one, which is how most miswiring starts.

Table 1. Pin assignments.