STK500

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Hey freaks.

This is a little hard to explain so please bare with me.
I have just recently dug out my STK500 and have it al connected up. I have it connected via a USB to RS232 converter and powered by a Digitor power supply. The device is working without issues. However, when it is turned on and plugged in to my laptop (which is made completely of metal) touching the laptop with my arm or finger gives me a little shock. Its like it is not grounded properly or something... when I run my finger across the top of the laptop, there is a kind of resistance and you can tell there is an electrical current present.

Something else I noticed is that the Digitor power supply makes a static noise when in use. I'm not sure how I can further explain what is happening but if you require more info please let me know. Has anyone experienced anything like this or have an idea what could be causing this?

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I would swap your 'Digitor' with a regular wall-wart.

Everything should end up using the GND from your laptop.

You only want one device that plugs into the mains with 3 pins. I do not know what Australian mains plugs look like. In the UK, an isolated device may have a plastic GND pin. Or a brass one that is simply not connected to anything.

Oh. The STK500 likes to have its DC supply with -ve tip and +ve barrel.

David.

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Thanks David, I assumed it would be the power supply. I think I may have another one laying around to test so I'll see how that goes.

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@David,
I noticed the power supply liking the barrel being V+ and it always bugged me as to why, because there is a bridge rectifier connected to the power input jack.

Hmmmmm gonna have to look at the schematic....someday

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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IIRC the STK500 has a bridge rectifier on its power supply input. Hence the polarity of the wall wart's barrel connector doesn't matter.

BUT, that means that what the rest of the STK500 considers to be "Ground", including all of the "Ground" pins on the 2x5 headers, etc., are actually sitting about 0.7 V off what the Wall Wart considers to be ground.

There was also another Thread where Nard posted his rather extensive Wall Wart testing which showed that the new switching Wall Wart's "Ground" isn't necessarily equal to Earth/Mains Ground.

From the other end the PC's "Ground" is tied to the USB Ground, then to the RS-232's Ground, and then to the STK500's Ground.

No surprise Ground <> Ground.

Solution:

Run your laptop on its battery, unconnected to its Mains power supply.

Or use an "old" Wall Wart, with a true transformer in it, for the STK500.

Or get an "Isolation Transformer", and plug either the PC's power supply or the STk500's Wall Wart, (either kind, old transformer model or newer switching model), into the isolation transformer's output. Note that the isolation transformer's output is then truely floating with respect to real Earth/Mains Ground.

I also have an "old" car battery under my work bench, and occassionally power stuff from it, (fused). I put it on a car battery charger once every few months.

Others may have further suggestions.

JC

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WEll I looked at the schematic and I remember the reason for the funky operation.

The power switch turns can possible turn off the ground side of the input. Hence if you have the rs232 connected, or the gnd of the stk500 is attached to some piece of equipment that can cause a ground loop the stk could conceivably keep running.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Quote:
so please bare with me.
I'm NOT that kind of a person....

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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js wrote:
Quote:
so please bare with me.
I'm NOT that kind of a person....

HAHA whoops... that vital 'e' makes all the difference