Is Arduino Output Dangerous?

I know it only takes very little current, ~10mA to start causing serious problems, like muscles locking up, etc. Not much more than that can kill you. Do I need to worry about this with Arduino output? The I/O output per pin is 40mA. How is this not dangerous? Especially grabbing a side of the circuit with both hands?

jwilkerson: I know it only takes very little current, ~10mA to start causing serious problems, like muscles locking up, etc. Not much more than that can kill you. Do I need to worry about this with Arduino output? The I/O output per pin is 40mA. How is this not dangerous? Especially grabbing a side of the circuit with both hands?

Because current flow is based on ohm's law and the voltages used in an arduino cannot force enough current through normal human body resistance to cause any sensation. You must first learn and have a good understanding of basic DC electronics starting with ohm's law. Current is not forced through something, but rather something's resistance and the voltage applied determine how much current will actual flow through a circuit.

Lefty

Wikipedia, which may be where you got the 10mA thing from, tells us that the human body's resistance is something like 100,000 Ohms.

Applying that to Ohm's Law (V=IR or I=V/R) as lefty rightly (haha) points out above, gives us 5 / 100000 = 0.00005 Amps which if I counted the zeroes correctly is 5E-5 or 50 microAmps. Certainly very small...

If it worked the way you thought, ie that current is pushed as opposed to pulled as lefty pointed out, and 5V at 40mA was lethal, how would anybody survive touching a 12V car battery which can supply 100s of Amps?

JimboZA: ...how would anybody survive touching a 12V car battery which can supply 100s of Amps?

Well - I wouldn't recommend doing that on a hot summer day after spending it wrenching on a car - it can be a bit...surprising.

/basically a very uncomfortable tingling...if you are really sweaty, tired, grease covered...wondering why that %$&^%! bolt won't come loose...

Well - I wouldn't recommend doing that... basically a very uncomfortable tingling...

Indeed, but we've all survived loosening the positive with the ground still connected and one hand on the fender.

Hands up all those who stuck 9V PP3s in their mouths as kids?

Yes I have my hand up. It was a standard way of seeing if a battery was flat before I could afford a multi meter. They were a bit more expensive in the 60s.

JimboZA:

Well - I wouldn't recommend doing that... basically a very uncomfortable tingling...

Indeed, but we've all survived loosening the positive with the ground still connected and one hand on the fender.

Hands up all those who stuck 9V PP3s in their mouths as kids?

As kids? Hell I still do touch them to my tongue, it's a good quick test to see if it's a dead battery or not and easier then getting the DVM out. Does taste awful though.

Lefty

They were a bit more expensive in the 60s.

Yeah...

My Dad, 97 this year, was an electronics boffin in HM's Royal Air Force and at Redifon (later known as Reduffusion Simulation, now part of Thales afaik) in London and Crawley. Circa 1962, I remember him making a multi-meter in a cigar box.. it was hugely impressive, with all manner of knobs and buttons and stuff.

He also built me a power supply for my Scalextric...

retrolefty:

JimboZA:

Well - I wouldn't recommend doing that... basically a very uncomfortable tingling...

Indeed, but we've all survived loosening the positive with the ground still connected and one hand on the fender.

Hands up all those who stuck 9V PP3s in their mouths as kids?

As kids? Hell I still do touch them to my tongue, it's a good quick test to see if it's a dead battery or not and easier then getting the DVM out. Does taste awful though.

Lefty

one up

DO NOT TRY THIS AT HOME!! :D http://www.youtube.com/watch?v=hp97GjuULX8

DO NOT TRY THIS AT HOME!!

I'm not even going to watch that

JimboZA:

DO NOT TRY THIS AT HOME!!

I'm not even going to watch that

Actually he is pretty funny. No torture allowed, unless your married. ;)

Lefty

Depends what kind of Output you mean. If you mean the Output force of an Arduino board orbiting Earth striking a space station, than yeah that would be dangerous for the crew living on the spaceship.

If you calculate: The mass of an Arduino board is about 25grams and various objects orbit Earth at a speed of 2000 m/s. Now we could find the momentum with this formula. p=m*v.

p=2000*0.025=50 kg/s

I think that is enough to treat a life.

If you are talking about the electric current from the Arduino being dangerous for you, then that is too boring to answer. But considering that you are a Newbie and this is your first post, I'm not going to say anything else.

Actually even relatively lower voltages (say a car 12 volt battery) can be quite dangerous from high current flow across rings and watches worn while working around such live circuits by causing a 'short circuit'. A gold wedding band can turn near incandescent in mere seconds and cause server burn injury if shorting out unfused high current circuits.

Lefty

To the OP who seems to have gone away then think of a kids electric train set. That has over twice the voltage output and twenty five times the current capability and we consider that safe.

retrolefty: A gold wedding band can turn near incandescent in mere seconds and cause server burn injury if shorting out unfused high current circuits.

"Near incandescent"? "Mere seconds"?

I accidentally dropped a wrench across the terminals of a car battery. The wrench melted into the terminals and turned bright orange literally within the blink of an eye. I am ever so grateful the thing lit up before I could grab it or I would have been off to the emergency room with a very very bad burn.

(ALWAYS wear goggles when working around a car battery. NEVER wear jewelry when working around a car battery.)

A gold wedding band can turn near incandescent in mere seconds

I used to work in telephone exchanges, where the 48V bus bars were bare.
However, the bus bars were stacks of centimetre-thick copper plates.
They were fed from banks of bathtub-sized lead-acid batteries, and main fuses were rated in high hundreds of amps.

We were told the (no doubt apocryphal) tale of the painter who put his paint pot across the bars, and pebble-dashed the ceiling as the metal pot vapourised.

Much later, we used 5V 200amp supplies to blow out internal shorts on multi-layer PCBs.

I still take off my metal bracelet watch when working on high amp gear.