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Topic: How much current can I drain to an Uno digital I/O pin? (Read 2192 times) previous topic - next topic

jack wp

I see no problem with your schematic in post #13. "Low frequency" is ambiguous, but I think the 500hz from the PWM would qualify.

amirf

I have tried drawing current from more than one pin and it goes close to 200mA. Still it didnt work for me as Fona 3G board needs closer to 500mA occasionally.

Robin2

I have tried drawing current from more than one pin and it goes close to 200mA.
That's crazy. I/O pins should not be used as an energy source.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

MarkT

Thank you -

I guess I just got lucky that my original functioning project didn't cook the Arduino, because the motor happened to be such a low current device.
Luckier than you think, the low current won't protect you from inductive kick-back.

If you switch inductive loads (motors are highly inductive, like relays, solenoids), then you _need_
to protect against kick back, typically with a free-wheel diode (in a DC circuit).

What was happening with the 30mA motor (which BTW probably drew much more than that
at stall), was the ATmega's input anti-static protection diodes were taking the current pulses
and acting as free-wheel diodes, despite them being rated for more like 1mA than 30mA.

If a protection diode were to fail, the inductive pulse voltage would be enough to blow away
the output driver for the pin, and perhaps the whole chip.

This sort of abuse typically leads to seeming random failure at some point in the future, and
is likely to bite back one day when least expected!

The pins on any logic chip like a microcontroller are for signalling, not for powering.  For convenience
the ATmega pins can drive very high currents (for a logic device), to make it convenient to
shine LEDs, drive opto-couplers, etc.  In general a logic signal might be rated for 5mA or so,
sometimes more, sometimes less.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Robin2

Two or three hours spent thinking and reading documentation solves most programming problems.

MarkT

Arghrgh! Zombie threads again.  Please don't activate a zombie thread without good reason!
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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