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Support Forum » Broken voltage regulator (7805)

June 01, 2010
by kyrre
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Hello.

i received the NerdKit a few weeks ago, but haven't had the time to start the temperature sensor project until recently. I wired the entire thing up, and... nothing. I went through all the wires, found some errors, and tried again, yet no luck.

After that I checked the battery with a cheap, analog multimeter I bought (I know, should have decked out for the expensive, digital, one), and it is completely fine.

I have a suspicion that it's the voltage regulator that is not working, however, I don't know how to test it using my multimeter (I'm a programmer, and knows next to nothing about electronics, that's is what I'd like to get out of this). Anyone that know how to this using a basic multimeter (no continuation testing)?

All help is appreciated.

Kyrre

June 01, 2010
by hevans
(NerdKits Staff)

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Hi kyrre,

What is exactly is it that makes you suspect a broken voltage regulator. It is certainly not the most likely chip to have fried if you connected something wrong (and it would have gotten really really hot in the process). The easiest way to test your multimeter is to see if it regulates power down to 5V correctly. Hook it up to three empty rows, connect a 9V battery to the Input and GND pins, and measure the voltage between the output and GND. Make sure you try this with a new 9V battery (you can check to make sure it is 9V with the multimeter) connecting a battery that is dying to the voltage regulator could cause strange results.

Let us know if you find the issue.

Humberto

June 01, 2010
by kyrre
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I think you are correct about the battery. The only thing is that I got the same results as another 9V battery I had lying around (old, but unused), but I suppose both could be dying. My multimeter said they were ok on the battery testing, but only about 4V when I tested the actual voltage (given I've read the darn thing correctly).

I'll try to get a new battery and multimeter tomorrow, and I'll get back to you on the progress.

June 01, 2010
by mongo
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An analog volt meter will do just fine for what you need to do here. They are not as accurate but for a quick check like this, close enough is close enough.

First thing, make sure you have a good battery. Looking at the 7805 face-on, the left pin is the "Bat +" terminal. The middle one is also tied to the tab on the back and is ground. That leaves the pin on the right as "+ V out" In this case, 5V. The ground is common to both the Bat + and + V out and you can pretty much expect that for most of these circuits.

With nothing else connected to the regulator, connect the battery to the first two terminals. Make sure the negative lead is the middle one. Check your voltage across those two terminals. it should read 9V if you are using a good 9 Volt battery. Now go to the third terminal. That one should read 5V between the middle and third pins.

If the battery voltage drops significantly as soon as it is connected, it can be a weak battery or a bad regulator. If the battery voltage continues to be about 9V and there is not 5V at the third terminal, it would be a bad regulator.

If these test OK, then start connecting the rest of the circuit. One mis-wired component can cause enough of a load to draw the regulator down so make sure + goes where it should and the same with -.

June 02, 2010
by kyrre
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I figured it out. It actually turned out to be the battery clip. I must have yanked it to hard when removing the battery from the clip, and broken it, somehow. I tested all the circuits the best I knew how, and since I probably broke the battery clip while testing the voltage regulator, I ended up blaming it.

I returned my cheap multimeter and got a more expensive one, which is a lot easier to use, but I still see some fluctuations when I test the voltage across test wires on the breadboard. I believe that to be because of a less-than-steady hand and lack of experience of using the multimeter.

I'll plow along with the temperature sensor project now, expect more beginners questions as I go along :-)

Thank you hevans and mongo for your help, I think most of my problems is due to the fact that I really don't know what I'm doing yet, your responses help make me feel less like Bambi on ice.

June 02, 2010
by mongo
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It's a learning curve that is some times difficult to stay on. Sounds like you are well on your way now. Good luck.

June 02, 2010
by kyrre
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Thanks! I have success :-)

Now for the rest of the temperature sensor project! This really rocks!

August 04, 2011
by jholladay
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I also just had an experience with what seems to have been a bad voltage regulator (from the get-go).

First project fired up right away (despite some troubles with the skinny leads on the battery terminal). No heat, no smell, no real trouble, but on multiple restarts it started being kind of flaky. Tested with a battery at 9.35 volts, and got 4.93 volts out of the regulator. The start-up time was varying (seldom instant), and the programmer wouldn't respond to chip erase on the first software load try. Also tried other batteries with varying results, but always flaky.

Cut over to USB (4.99 volts) and all problems went away. Start up seems to be instantaneous. Found an extra 4805 in a radio shack electronics lab I have, measured at exactly 5.00 volts, and when I used that regulator it worked perfectly, just like when on USB.

I'm kind of surprised because I thought that the digital signal would work okay between 4.5 and 5.5 volts, so it seems like 4.93 should be good enough. Any thoughts?

August 05, 2011
by Rick_S
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My main thought would be this.

Most of those regulators have a +/- 5% tolerance on their output. So under a no load condition, and good input power, their output could vary from 4.75 to 5.25 volts and be considered a good device. So 4.93 is totally normal.

9V batteries have a typical max current output between 150 to 180ma (excluding rechargables which can have more current but typically lower voltage at 8.4). As such, it is very easy to draw more current than the battery is capable of supplying if you build the circuit up. Couple this with the extra current required to erase and flash the chip and you will have problems. If the battery isn't at 100%, and even new ones aren't always, you may see erratic issues. This is one reason either USB or an external supply becomes much more user friendly. I would also venture a guess that if you could have seen the voltage of your battery and regulator at the moment in time of the problems you would have see drop outs.

Just my 2 cents worth...

Rick

August 05, 2011
by jholladay
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Hi, Rick.

Thanks for the reply. I feel like I wish that the very first project wasn't pushing the limits of the contents of the kit. I was hoping that I could wait to experience an issue like this after I get my feet wet and start putting heavier demands on the system. Alas...

Is there an inexpensive tool that can be used to diagnose this sort of thing? Or is trying new batteries, replacing components, etc. the standard approach at this level? Is it just a matter of always assuming that a 9v battery is inadequate for most projects? I know I can just switch power supplies or voltage regulators and move on at this point. But I'd like to think there's a more elegant way of reaching a solid conclusion on what was going on (or just adding a strategic capacitor or something minor and within the spirit of the 9-volt battery project).

Is there a little battery test circuit that I could whip up? I suppose I could google that...

Thanks. Jason

August 06, 2011
by dgikuljot
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@Jholladay To test the battery clip, or any other electrical wire you would do a continuity test. On the multimeter the symbol for this test is like a arrow pointing to the right with a plus sign attatched to it. So once you are on that, attatch one of the multi-meter leads to the terminal on the clip, and the other lead to the wire that terminal is supposed to be connected to. depending on your multi-meter if it has audible continuity test it will beep. Or on the screen if it shows a solid 1 that means there is no conenction and if it shows anythign else that means the connection is good. If you need any clarification ask us, or just google how to do a continuity test.

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