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VCC
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VCC

by westbrookp1 on Thu Dec 03, 2009 12:51 pm

I have a functional usbtinyisp. When i look at ladyada's picture of hooking up the avr, she hooks it up coming down the board. While investigating my usbtiny, I think the VCC is switched. So my question is, should the 6-pin attachment be hooked up coming up the board? Also, Should we be supplying 4 volts into the board while we are hooked up to the avr?
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Re: VCC

by hjohnson on Sun Dec 20, 2009 10:28 pm

Well, how do you mean "switched?" In what way? In order for the flip to work, the whole assembly would have to be rotated 180º, not just VCC. Check your schematics, and make sure you are right on this. If you post photos, I can check as well. (I also own a usbtiny.)

How do you mean supply 4 volts into the board? The only power that the usbtiny needs is USB. If you want the usbtiny to power the avr, leave the jumper on the non-usb end in. If you want your avr to be powered independently, take the jumper out.
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Re: VCC

by Mictronics on Sat Feb 20, 2010 3:45 pm

VCC is running at 3.3V and supplies also the NE555D, right?
I just wonder if this is fine for the NE555 since the IC is rated for 4.5V minimum supply.

Any problems with that so far?

And a thought about the design:

Why not take VIN for the TPS79333 from the +6V rail. The TPS793xxx is rated anyway up to 6V VIN.

Why?

The TPS793xxx is an LDO which means output voltage drops when VIN drops below the regulator voltage. Which means the output of the TPS79333 will drop when the LiPo voltage drops below 3.412V.
When VIN would be +6V the LiPo could be drained some more.
/Michael
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Please be positive and constructive with your questions and comments.