Killed my laptop it seems

Projects General Guidance
1

Basically, i tried to vary the speed of the dc motor, using a pnp transistor, connected the base of transistor to analog pin of arduino, which would be variable

I had used a 12v adapter to power the motor through the transistor, however the arduino was powered through the laptop's usb.

Hence for the transistor to work, i had to connect the adapter's ground to the arduino's ground

Now i think, that's what caused the problem, i think the "ground" of the adapter had voltage, which through the arduino connected to the laptop's ground and killed it.

Anyways, the instant i connected the adapter, a blue screen appeared on the laptop and it shut down, so i disconnected the adapter, and now the laptop doesn't turn on.

Note to self: Don't use external power supply and laptop connection at the same time

Edit:
Well folks I took John's advice and it worked! when i touched the laptop it was somewhat
hot, meaning it was running although the screen was off, i figured to take out the battery and when i put it back in, it started normally! also the port itself was not damaged as well, so that's great too. I thank you all for your help trying to figure out the problem

Here is some more info on what i did:
now I measured that usually the motor takes 100mA at 12V. and the Hfe of the transistor was 300, so current through base would be 100/300 = 0.34mA, and with 0.7v drop across base-collector, resistor at base would be (4.3*1000)/0.34 = 12,650 -120 = 12,530 ohm. (120 is resistance of the motor itself). i obviously did not have an exact resistor for this resistance, so i put 10k and 2.2k resistors in series to make 12.2k resistance. Then i connected the the base to the A1 pin of arduino(through the resistor ofcourse). Now my thinking was, that reducing the voltage at arduino's pin would therefore reduce base current, which would reduce collector current, and slow the motor down.

hopefully this is right, i'm new to this and have no prior experience in electronics so i'm not sure(as you probably would have guessed by now)

also this is the circuit(A1 is analog pin of arduino):

Circuit
Circuit1599×1599 102 KB

2

Hi,

Did you have the adapter turned ON, when you made the connection?
If the computer was connected, the Arduino would also have been ON.

NOT GOOD PRACTICE.

Can you please post an image of the 12V adapter?

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

1 Like
3

Most likely your laptop motherboard can be fixed.

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4

What ever you think, if what you describe is what you actually did then making the grounds common is not what killed it.

You need a common ground when using external power supplies.
See this
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

Can you draw a schematic of that part, because as it stands it sounds wrong. Did you use any resistors?

Should read Note to self, learn more about circuits before you use them.

My guess is that your circuit put 12V into the USB and that is what killed the laptop.
Plus what Tom said about never connecting up circuits when they are powered up

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5

Disconnect all power sources (PSU, batteries) from the laptop, wait a few minutes, then try to turn it on.
Also, push the reset switch if it has one (usually under a small hole on the bottom), or disconnect the CMOS battery.

It is very possible that the laptop may start up after this. The USB controller may have burned already though.

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6

Next time, use a switch on the USB red wire.

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This was one of the first things i built when i got into Arduino.

2 Likes
7

Hello
Did you also print the thread for the housing?

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8

Yeah. You want a copy of the .STL? I added rounded corners to the design.

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9

Hello
I´ll use FUSION360 to design the box by myself.
Many thanks.

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10

Fusion360 is overkill. I use TinkerCAD. Its free and easy. I just use F360 for generating dimensioned drawings, but for simple stuff its overkill - and expensive.

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11

II just go and buy one or look in the junkbox ..... KISS :laughing: :sweat_smile: :laughing: :+1:

Tom... :smiley: :+1: :coffee: :australia:

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12

It probably would be "smart" to use a powered USB hub. If something goes "terribly wrong" you are likely to fry the hub without hurting the computer. (Personally, I don't use a hub.)

I don't know if you can find an optically-isolated USB hub or isolator but that would be ideal.

I often power an Arduino with 12V through the barrel jack while connected to the computer. So far, no problems.

Most USB ports are short-circuit protected but over-voltage (or high reverse voltage from inductive kick-back from a motor) I don't know.

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13

12v thru the barrel is tough on the onboard +5 regulator. These have a nasty tendency to fail short & apply the full input voltage to Vcc. 12 to 5 is a 7v drop and at 100mA is .7W, too high. Reducing the input to 9v brings the drop down to 4v and at the same 100mA the load is .4W, still not "cool running" but lots better than .7W on a SOC package.

I run Mean Well 5v at 3A medical grade world wide approval PS's with a USB switch for Vcc isolation.

https://www.jameco.com/z/GSM18U05-P1J-MEAN-WELL-5-Volt-3-Amp-15-Watt-2xMOPP-Medical-Wall-Adapter_2278919.html

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14

While no doubt by your description something happened to your laptop. However most laptops (if not all) are isolated from the mains ground. And most (again if not all) 12V adapters are isolated from ground.
So in theory there should be no fault current(s) when you connect the two grounds together. So is it possible the +12V became connected to the USB 5V?

In practice I've found the electrical noise between the two have wreaked havoc on my circuits, however I've never fried my laptop.

None of this likely helps you, however I suggest you draw what you have connected and post the drawing. I'm guessing there is a "sneak circuit" that does things you do not want to happen.

A sneak circuit is a term for an electrical path the exists through a device that wasn't obvious when the circuit was designed.

As for your laptop, I would remove the batteries and let it sit for a while. Reinsert the batteries and try again.

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15

Hi,
Can you post images of your project?
The motor, transistor and its connections.
Also what 12V supply are you using?

Thanks... Tom.. :smiley: :+1: :coffee: :australia:

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16

The adapter was off as well as the arduino, only after making the connections, i connected the arduino and then the adapter which caused the mess. the adapter is a pretty cheap, it cost me 100INR, which converted to USD is 1.3 dollars so yeah.....

also the adapter was off when i made the connection, however the arduino was on

anyways, here it is:

Adapter
Adapter1599×1599 201 KB

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i have uploaded a drawn circuit, however i took apart the connections yesterday so i can't upload that, sorry...
the transistor is 2n3906, the adapter is a pretty cheap one which i have uploaded as reply to your other comment, and the motor has no company marking on it whatsoever, and i forgot it's specs as i bought it some years back and never used it till today, tbh it rotates and that's good enough for me(probably why i can't make any of my circuits work)

18

YES! as it turns out you are very right, i took out the battery and i worked! so thank you for the wise solution. also i have uploaded the circuit as an edit on my question

19

Hi,
Thanks for the info, we need to know the current that the motor is rated at.
Possibly you could have cooked the transistor and caused 12V to get on the input circuit.

Tom... :smiley: :+1: :coffee: :australia:

1 Like
20

I just connected the motor through a multimeter to 12v, and the current through it was about 100mA so i figured that was the motor's current, is that right? Because i made all of my calculations based on 100mA through the collector.