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# Thread: What is the maximum current a digital output pin can pass through itself?

1. ## What is the maximum current a digital output pin can pass through itself?

What is the maximum current a digital output pin can pass through itself?
What is the maximum amperage of the load Teensy can drive at 3.3v?

I see that it can drive an LED through some diode of unknown value. Maybe 50kOhm. Not sure. I cant find the Absolute Maximum specks for this wonderful hobby microcontroller product.

2. I think the maximum per pin is 10ma, when driving less make sure not to go over that. Usually LEDs are rated between 20-25ma depending on the color, so you will need a higher valued resistor than what you would normally use for that voltage.

3. See this answer by Paul for a more detailed explanation:

4. usually differs in sourcing vs. sinking current.

5. To drive a LED with 25 mA, a transistor or buffer chip is best.

However, you might try testing the LED you're using. Many LEDs have non-linear brightness vs current, where you get diminishing returns in brightness as you approach or exceed the rated max current. The human eye is also similarly non-linear. Most modern LEDs are pretty efficient, where 10 mA might be plenty to make it appear bright enough. With many LEDs, even 5 mA is plenty. But not all are so efficient. Sometimes 20 mA really is best. Just flowing a test current through the LED for a few seconds will give you a lot more insight than hours of studying specs.

Often the required current depends on the surroundings. A LED poking through a hole in a dark colored material is a lot easier to see that one which has other bright stuff nearby.

If you have a lab bench power supply with adjustable voltage, a 1K resistor in series with the LED is the easiest way to test. Put a voltmeter across the 1K resistor, where each 1V read is 1mA in the LED, and then play with the voltage knob to find brightness that works well.

6. A closely related question - how much capacitance can one put directly on an output pin? Either teensy 3.2 or 4.0.

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