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Topic: Arduino on a Breadboard: problem with 7805 voltage regulator, blew up LEDs! (Read 2605 times) previous topic - next topic

BernieG

Jun 11, 2016, 06:05 pm Last Edit: Jun 11, 2016, 06:24 pm by BernieG Reason: added power supply
I am wanting to make the project described here: https://www.arduino.cc/en/Main/Standalone
and I started by wiring the power supply, as explained.

But at my first couple of tests, the Led blew up!

I checked and doubled checked my wiring, looks OK.

Doubling the resistor to 660 Ohms keep the Led alive, but I can see on my multimeter a quick surge to about 8 volts, before the current stabilize properly to 5.02 Volts exactly.

I am afraid the Atmega 328 will not like this 8 Volts surge. What should I do to eliminate it?

Thnaks for your help,
Bernard

PS- Forgot to say, Power In is regulated 12 Volts, 11.99 exactly.

raschemmel

Welcome to the forum Bernie.
Unfortunately , you are not familiar with the protocol here. There is nothing we can do to help you based on your post , since it tells us virtually nothing.
Here's what you need to do:

1- Identify what "led " you are referring to by exact connections (ie: "led cathode connect to [blank], led anode connected to [blank] (fill in the blanks)
2- Identify your power supply source (where is your power coming from ?)
3- Identify how you are connecting to the atmega328 (do you have an FTDI ?)
4- Identify EXACTLY WHERE you measured 8V and HOW (METER ON WHAT MODE/RANGE /SCALE ?)
5- Post a photo of you circuit taken with a cell phone held DIRECTLY ABOVE about 12" away.
6- Draw a simple schematic of how you connected the led on a blank sheet of printer paper and post a photo of it.
7-Explain EXACTLY how you constructed the circuit (ie: did you use a schematic and make a connection and then highlight that connection with a yellow highlighter to indicate it was done ? Did you simply read the tutorial and connect parts with no written documentation in front of you as a reference ?)
Have you ever looked at the datasheet for an ATmega328 ?
Do you have any experience using a DMM ? (if so , how much ?)

In short Bernie, your post is unusual because that tutorial has been on the forum for years and to my knowledge no one has ever claimed a led blew up after following that tutorial. That is the same tutorial I used to learn how to breadboard the ATmega328 (I have four breadboarded at the moment, all working fine). Needless to say, if you are reporting a led blew up , you have done something terribly wrong because in 35 years of professional electronics experience , the only leds I ever saw blow up were exposed to voltage without a current limiting resistor and they didn't actually "blow up" like a transistor would , but rather just stopped working. What you are reporting would seem to be due to "operator error".  The chance that a led connected with a 330 ohm resistor would blow up is slim to none. The only conclusion I can come to is that you never measured the resistor with the ohm meter and actually used a 33 ohm , instead of a 330 ohm. Measure the resistor with the ohm meter.

If you breadboarded the LM7805 5V regulator , you probably connected the 12V input  to the led instead of the 5v output. The 12V could "blow up" the led much easier than the 5V. Post a photo of your 5V regulator wiring, along with the led circuit.

BernieG

#2
Jun 11, 2016, 08:23 pm Last Edit: Jun 11, 2016, 08:33 pm by BernieG Reason: Images not showing up
Thank you for your fast answer, raschemmel. Let me try to explain more clearly, as it seems you did not understand that I HAVE NOT connected to the Atmega328, yet. (happlily, it seems!)

- First, the actual wiring:


This is the last evolution of my attempts: the 2 long red and black wires are coming from my power supply, which is a computer PSU unit, giving me 12 volts regulated.

I have 2 capacitors on the IN side, 100µ each, and 1 on the OUR side, 10µF

The led is now connected with 2 330 Ohms resistors in serie, giving 660 Ohms measured, connected to the Anode (+) and actually light without stopping (maybe blowing up is a strong word, but I never experienced that before, 2 Leds stopped working immediatly after turning power up!)

- Picture showing it does work:


-Very short video showing the multimeter display when I turn power ON, it show 7.87 volts before going down to 5.01 Volts (it's fast, so you have to look carefully!):

https://youtu.be/qhDyVcek2m4

So, my real question/problem is: is it normal to have such a power surge, and with the Atmega328 absorb it, or is there a risk to damage it?

raschemmel

While it may seem "convenient" to use a computer power supply, it is actually the wordt decision you could make fir what you are doing. It is capable of delivering enough power to literally "blow up" a small TO92 package transistor, sending high velocity fragments shooting all over the room. Do not allow any children within 15 feet of your circuit unless you want to blind them when the fragments hit them in the eye because you miswired something. It is an accident waiting to happen. I watched an 8-pib LM555;burstbinto flames on a bteadboard and glow red as it melted the breadboard. Unless you are poor get yourself a variable voltage  , current controlled bench lab supply (0 - 30V , 3A). If you can't afford that get a 12V/1A AC/DC adaptor wall wart.  What you are doing is the automotive equivilent of giving a teenager with NO driving experiencd the keys to a 700 hp Dodge Viper. ( good luck with that)

Your video is bogus. Put a scope on it and you'll see that it is proobably a meter problem . If you use a voltage divider to measure the voltage with an analog input you can see if the surge exists.
If the meter is on the iutout of the regulator I diubt it. I've been usung KM7805s for 35 years abx never observed such an "anomaly".

BernieG

Ha, thanks! So, if I understand what you're saying properly, my "problem" with that surge could be because I use a pretty bad power supply? My multimeter show it's VERY stable (to 1/100 of a volt), but it may have too many amps?

Anyway, thanks for your advice, I will find one "real" power supply.

Bernard

groundFungus

Compare how your regulator is wired with this pinout image. 


BernieG


raschemmel

Thst's not what I said at all. Reread my post. I said a beginner should not be allowed to use such a powerful supply because it's like playing with dynamite. You are one miswire away from hurting yourself or others or starting a fire. Don't cry when your house burns down because you miswired something and fhe piwer supply pumped 30A into a little chip. POOF !

 It has nothing to do with your 'imaginary" surge which I doubt exists despite what your meter says. Think about it. Is it more likely that a part that has a reputation of 50 years of reliable operation is suddenly "surging" on power up or more likely thst it takes your meter a moment to stablize ? What brand/model meter is it anhway ? ( how much did it cost ? Is it a FLUKE ?)
An LM7805 is a one trick pony. It does one thing and one thing only.It either dies or does not regulate. IF it regulates, it regulates from the moment of powerup . It foes NOT "overshoot" or surge. In short, your meter is crap and it is misleading you. Until I see a scope screenshot of the "surge" I will not believe it us real.   I have never seen an LM7805 overshoot on powerup in 35 years.

Paul__B

It's an auto-ranging meter.  To do this you must pre-set the range before you make the turn-on measurement.

Do that and tell us the new observation.

Grumpy_Mike

Your LED blew up because you did not have a resistor in series with the LED. The picture shows both ends of the resistor being connected to the same column of the bread board and so it is shorted out.

We need a schematic of how you have wired things up, so we can check that is correct. Then we need the photograph to see if you have wired up your bread board like you intended.

raschemmel

Quote
Your LED blew up because you did not have a resistor in series with the LED. The picture shows both ends of the resistor being connected to the same column of the bread board and so it is shorted out.
  
NICE CATCH MIKE !

I couldn't see it because I wasn't at home and it was hard to see on my cell phone.

I knew it was operator error !

@OP,
Your led only has 330 ohms because the first 330 ohm resistor has both leads shorted to each other !
The second 330 ohm resistor goes TO +5V.

BernieG

It's an auto-ranging meter.  To do this you must pre-set the range before you make the turn-on measurement.

Do that and tell us the new observation.

Thanks you Paul, you nailed it! Pre-setting the range do it.
Like I said, I am a beginner electronics wise, and did not think it could be the cause for this apparent surge.

Anyway, thanks to all, I am glad about this, because it was the opportunity to learn a couple of important things.


BernieG

NICE CATCH MIKE !

I couldn't see it because I wasn't at home and it was hard to see on my cell phone.

I knew it was operator error !
Sorry, but this is not true. Maybe the picture is not clear enough, but the wiring has no problem, otherwise how would you explain the picture with the Led on and 5 Volts displayed on the Multimeter, as well as the video?

No, it's simply that I have to preset the range on the autorange multimeter.

raschemmel

Quote
Sorry, but this is not true. Maybe the picture is not clear enough, but the wiring has no problem, otherwise how would you explain the picture with the Led on and 5 Volts displayed on the Multimeter, as well as the video?
Yes it is true. Zoom in on the both photos. The led is on because your connected the SECOND 330 ohm resistor correctly. You can see the first resistor with BOTH leads in the SAME ROW ! (in both photos ).


The miswired resistor has nothing to do with the meter range.

You need to stop listening yourself and start paying attention to the experts you are consulting. You have been wrong on all counts from the start:
1- You blew up the led. The led didn't blow itself up.
2- there was no surge
3- the led is on because you added a second resistor. Mike told you what the problem was and you still can't see it. It's plain as day. the first resistor has both leads in the same row.

raschemmel

Quote
Anyway, thanks to all, I am glad about this, because it was the opportunity to learn a couple of important things.
What you SHOULD have learned:
1-there was no "surge" to begin with. It was your inexperience using the meter, nothing more.
2- the LM7805 WAS regulating on power up, just as I said.
3- you miswired the first 330 ohm resistor causing the led to "blow up"
4- You are too inexperienced to be using a 12V power supply capable of delivering 20 to 30 A because the first time you miswire something you're going to blow something up or start a fire. Get a different supply and get that computer power supply far away from your electronics before you hurt someone.

From OP
Quote
But at my first couple of tests, the Led blew up!

I checked and doubled checked my wiring, looks OK.
 
Based on this post, maybe in the future you should check three times...

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