Recipe

Can this pin drive it directly?

Use when: you want a pin to turn something on, and need to know whether it may connect straight to the pin

Goal: a yes with a calculated current under the pin's limit, or a clear no that sends you to a switch

Taught in GPIO is not a power supply

1. 1

   If the load is a motor, relay coil, solenoid, speaker or anything else built around a coil, the answer is no.

   Example

   A vibration motor, however small: no, because it kicks back a spike when switched off.

   Why: a coil's kickback is the danger even when its current is small, so no calculation can make it safe on a bare pin.

2. 2

   Calculate it with Ohm's law, or read it from the load's datasheet.

   Example

   A red LED with 470 Ω on a 5 V pin: (5.0 - 2.0)/470 \approx 6.4 mA.

   Why: the load sets the current; the pin can't hold it back.

3. 3

   Use the board's or chip's datasheet; never a number from memory or another board.

   Example

   Uno R4 Minima: 8 mA (Arduino datasheet, section 9.3). ESP32-S3: about 20 mA at the default drive setting (Espressif datasheet, Table 5-4).

   Why: limits differ by chip, and a number from another board can be off by several times.

4. 4

   The load should sit comfortably under the limit.

   • it does — it may connect directly; also add up every loaded pin against any total limit.
   • it doesn't — put a switch between the pin and the load (the next three sections).

   Why: parts vary from their typical values, and a pin run at its limit sags and heats.