A follow up to my earlier question about UNO pins. Data sheet says UNO input should be
7-12volts. Any reason I can't power a 5vDC relay pack with the 5v pin on the UNO??
Power supply would be 12v/5A more than enough to drive everything. Question is
what could the 5v pin handle?? are we still talking milliamps?? Total load on the relays
would be 640mA. Any info appreciated.
Several reasons. The voltage regulator will overheat and shut down if you try to draw more than about 150 mA, depending on the input voltage. At 12V input you can't draw even a fraction of that.
Relays, motors, servos and the like also inject electrical noise into the power supply, possibly resetting or damaging the Arduino.
Basic Rule: the Arduino is not a power supply.
A solution for the problem may be powering both relays and arduino from 5v power supply
Again, thanks for responding. So what would be the highest (or safest) output from an Arduino. I'm
thinking about a Mega with it's 50+ outputs, at 20mA per pin, and all pins high, that's 1A. Is there a "safe" percentage you should stay below or do I just assume each piece was designed to have all the pins high at the same time. I want to light as many LED's at once as I can by programming without killing anything. Should mention this means high for 1/2sec. then low. Thanks again
From the data sheet...
31. Electrical Characteristics
Absolute Maximum Ratings*
Operating Temperature.................................. -55C to +125C
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to V CC +0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
*NOTICE:
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent dam-
age to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ................................................ 40.0mA
DC Current V CC and GND Pins................................. 200.0mA
So the max for all active pins is 200 ma.
Simple rule:A Power Supply the Arduino Is NOT!
Thanks, printed that out.
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