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Topic: How to protect arduino from overcurrent (Read 3619 times) previous topic - next topic

Grumpy_Mike

#15
Aug 26, 2017, 10:01 pm Last Edit: Aug 26, 2017, 10:02 pm by Grumpy_Mike
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Does it works the same way?
A reed switch and magnet on the door works in exactly the same way.

I do post occasionally on other forums, mainly the Raspberry Pi.

maxwell1

@grumpy_mike

I have few questions running through my head if u don't mind asking them.

Exactly the same way.
But!

Mike's answer was for a manually operated, normally open switch.

If the switch is going to be closed (with the magnet) most of the time, it will be useless as the battery will quickly go flat.

1st I got such suggestion from paul but donno what is solution if this is the case?


2nd won't it be dangerous is someone cut the wires between the reed switch and the opt and inserted it into electric outlet or any power outlet with high voltage and current while there is battery in between which might cause explosion?? I don't mind the opt to melt or get fried or damaged but I care about the uino and of course the place and I don't want any harm to either of those?


3rd is it better to roll around the opt and thr wires connecting to it an electric isolator tape to protect the surroundings incase it got fried or any bad case scenarios happened or it might cause problems in the long run?


4th is it better to wire the wires directly to the opt or I can use breadboard?
I have feelings that it would be safer to do it directly for some reason than on breadboard in case of high current and voltage


5th i am using 9v battery cuz AA battery holder wasn't available in the nearest elec. Shop so how i can calculate resistance needed for the opt when using the 9v battery?




Thanks a lot and really appreciate your support especially grumpy_mike, paul_B and of course the rest as well and apologies for long post


Max

Grumpy_Mike

#17
Aug 29, 2017, 03:35 pm Last Edit: Aug 29, 2017, 03:37 pm by Grumpy_Mike
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If the switch is going to be closed (with the magnet) most of the time, it will be useless as the battery will quickly go flat.
If the magnet is going to be in contact all the time you would use a normally closed switch, this will open when the magnet is removed. In fact I used an identical arrangement to turn off a Drum I designed for autistic kids. When a magnet is removed the drum turns on, when the drum is put away the teacher places a magnet on a specific indentation in the drum to turn it off.

Quote
won't it be dangerous is someone cut the wires between the reed switch and the opt and inserted it into electric outlet or any power outlet with high voltage and current while there is battery in between which might cause explosion??
Yes that could happen but we are talking about isolating the Arduino here. It could be equally as dangerous if someone doused your front door with gasoline and set fire to it. That is much more likely than your high tech bandits rewiring things. So far you haven't given us any justification as to why you think this is even a remote possibility.  

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3rd is it better to roll around the opt and thr wires connecting to it an electric isolator tape to protect the surroundings incase it got fried or any bad case scenarios happened or it might cause problems in the long run?
Things like tape will compromise the isolation properties of the opto switch - avoid it.

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4th is it better to wire the wires directly to the opt or I can use breadboard?
For any circuit you want to last longer than a day or two you can not use solderless bread board.

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5th i am using 9v battery cuz AA battery holder wasn't available in the nearest elec. Shop so how i can calculate resistance needed for the opt when using the 9v battery?
Replace the 5V with 9V in your calculations:-
resistor = (9V - (LED's forward voltage drop))/ required current

Note encasing a system in epoxy potting compound is a good way to vandal proof most things.

maxwell1

#18
Aug 29, 2017, 05:38 pm Last Edit: Aug 29, 2017, 06:01 pm by maxwell1
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Yes that could happen but we are talking about isolating the Arduino here. It could be equally as dangerous if someone doused your front door with gasoline and set fire to it. That is much more likely than your high tech bandits rewiring things. So far you haven't given us any justification as to why you think this is even a remote possibility. 
So it's not still safe to do the opt as if someone inserted the wires connected from magnet reed to opt to main outlet it will lead to the battery explosion and maybe other losses from the surroundings which is not what I want.

I really began to give up lol. Seems I am seeking something hard to be done or impossible. I really care about the uino not to be harmed as well as the place of course and I want some cheap solution that won't cost more than the uino itself but idk it's seems bit complicated to achieve such thing.

@Grumpy_mike trust me I know this scenario that amaze you can happen and it's the first and most easy to think about way to destroy the project and feel safe

Anyways I am still waiting more suggestions if anyone have any.


Thanks a lot

Max

MorganS

Look for an introductory lesson on fuses. Fuses protect wires from accidents and idiots. Sometimes you let the wire itself be the fuse: any significant fault current will melt the wire and make it stop conducting.

I second the "armoured cable" idea. If the wire is run through the wall or ceiling, it would take an extremely talented fool to pull the wire out and drag it over to a mains outlet.

Who was it that said "Sufficiently advanced stupidity is indistinguishable from malice"?
"The problem is in the code you didn't post."

Grumpy_Mike

Quote
Seems I am seeking something hard to be done or impossible. I really care about the uino not to be harmed as well as the place of course and I want some cheap solution that won't cost more than the uino itself but idk it's seems bit complicated to achieve such thing.
Well it seems to me that you keep moving the goal posts. A fuse in the battery would stop it bursting into flames. And would seem to answer this latest objection.

maxwell1

Thanks grumpy and everyone and really sorry for any bothering :S. I really appreciate all your time and help, guys. Hope I wasn't that annoying lol :S...


Thanks again,

Max ^^

maxwell1

#22
Sep 08, 2017, 11:32 am Last Edit: Sep 08, 2017, 11:52 am by maxwell1
@grumpy sorry for bringing this topic up again but wondering how to calculate the amount of fuse needed just for the battery to feed the opt isolator and to avoid the main outlet current to reach battery by burning the fuse before it reach it?

Btw, I am following your scheme u provided in previous post.


Thanks alot,

Max

Grumpy_Mike

Just use as small a fuse as you can get. You need it to blow at anything over 40mA but you can't get fuses that low so use the lowest you can get, maybe 250mA.

Southpark

#24
Sep 09, 2017, 02:36 am Last Edit: Sep 09, 2017, 02:40 am by Southpark
but what I am doing is I try to connect a door switch to the uino but as I need to be 100 percent secure that the uino won't be destroyed if someone intentionally cut wires of the switch and insert it in 220v electric outlet for sake to destroy the project
If this is for a security project or security system, then the switch and wires would usually be on the internal side of the door, where somebody isn't supposed to be able to access, right?

If somebody does want to tamper, then set up some kind of motion detector, alarm, lights, and camera to catch the culprit that is trying to interfere with your door switch.

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