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### Topic: Is Arduino Output Dangerous? (Read 4836 times)previous topic - next topic

#### jwilkerson

##### Mar 16, 2013, 04:53 pm
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?

#### retrolefty

#1
##### Mar 16, 2013, 05:11 pm

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

#### JimboZA

#2
##### Mar 16, 2013, 05:25 pmLast Edit: Mar 16, 2013, 05:26 pm by JimboZA Reason: 1
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?
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### cr0sh

#3
##### Mar 16, 2013, 06:07 pm

...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...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

#### JimboZA

#4
##### Mar 16, 2013, 06:11 pm
Quote
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?
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### Grumpy_Mike

#5
##### Mar 16, 2013, 06:14 pm
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.

#### retrolefty

#6
##### Mar 16, 2013, 06:17 pm

Quote
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

#### JimboZA

#7
##### Mar 16, 2013, 06:20 pm
Quote
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...
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### Jantje

#8
##### Mar 16, 2013, 07:58 pm

Quote
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 PM me a question unless you are prepared to pay for consultancy.
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#### Lakes

#9
##### Mar 17, 2013, 01:12 pm
DO NOT TRY THIS AT HOME!!

#### JimboZA

#10
##### Mar 17, 2013, 01:17 pm
Quote
DO NOT TRY THIS AT HOME!!

I'm not even going to watch that
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### retrolefty

#11
##### Mar 17, 2013, 02:37 pm

Quote
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

#### mixania

#12
##### Mar 18, 2013, 01:43 am
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.

#### retrolefty

#13
##### Mar 18, 2013, 02:02 am
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

#### Grumpy_Mike

#14
##### Mar 18, 2013, 05:59 am
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.

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