STK300 clone and target voltage level

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#1
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Hi,

Authors of the "classic"
STK300 clone
claims that their circuit will work for target with 3.3V supply.

Does anybody try this?

Regards

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arturl wrote:
Hi,

Authors of the "classic"
STK300 clone
claims that their circuit will work for target with 3.3V supply.

Does anybody try this?

I think that is the circuit I worked from when I needed another programming dongle, and yes it works at 3.3V as long as you make sure you use a 74HC244, and not an LS244.

So I suppose the HC is effectivly also being a level shifter between AVR@3.3V and Paralell port @ 5V.

Phill.

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Thanks Phill.
I was a little afraid (about my targer board) and you repsonse give me some boldness to try it.
It works.

Regards,

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arturl wrote:
Thanks Phill.
I was a little afraid (about my targer board) and you repsonse give me some boldness to try it.
It works.

Hey no probs,

I found out the hard way that an LS didn't work...built one which at the time was using with 5V stuff, needed to run at 3.3V when playing round with Igor Plug, and found it wouldn't go, checked and found I was using an LS (cause I ahd one in my spares box), replaced it with an HC and hey presto it worked !

I wonder if a standard HC would work in a more general sense as a 5.0<-->3.3 level shifter...have to give that a try.

Phill.

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If you supply the HC244 from Vtarget via a diode , and Vtarget is 3.3v , then the HC244 would get 2.6v , that might be ok.
But the HC244 would still get 5v on inputs from the PC Parallel port , i don't know if that is OK with an input voltage above VCC (even though it works)

Maybe some electronics wizzard could comment on that.

Otherwise its a neat trick.

/Bingo

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Bingo600 wrote:
If you supply the HC244 from Vtarget via a diode , and Vtarget is 3.3v , then the HC244 would get 2.6v , that might be ok.
But the HC244 would still get 5v on inputs from the PC Parallel port , i don't know if that is OK with an input voltage above VCC (even though it works)

Maybe some electronics wizzard could comment on that.

Otherwise its a neat trick.

/Bingo

Actually no diode in supply from vtarget, I tend to use polarised ISP connectors, so have not managed to reverse polarise....yet :) Then again a HC244 is only a few pennies, no no great loss if I do fry it :)

So HC is running off 3.3, and PC paralell off 5..so not as great a difference.

Phill.