usbtinyisp design
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usbtinyisp design

by buhman on Sat Aug 11, 2012 9:47 pm

Continued from: viewtopic.php?f=20&t=31890

[EDIT]

1) It is not directly possible to simultaneously power the usbtinyisp from the USB host and isolate the USB power from the target board.
2) The usbtinyisp is using 5V signaling rather than using a LDO as intended which is a direct violation of the USB standard, and could potentially damage the USB host.
3) The 1.5k pull-up resistors are far too small in the case where we want to do poor-man's level-shifting.
4) Digikey part 151-1081-ND is constructed in such a way that makes it very easy for the connector to short internally. It is flimsy, and is not forgiving with respect to mechanical stresses.
5) The IC2D symbol on your schematic is flipped the wrong way.
6) You are not taking proper care to eliminate digital switching noise on the 2313, and have not decoupled the MCU from the power rails appropriately, creating a condition where a high-current loop across the entire Vcc rail is possible, rather than just between the capacitor and the MCU.
7) Using a resistor alone as a pullup for the reset pin is non-optimal.
8) Being a fairly high-speed USB device, a resonator could cause more trouble than it's worth when communicating with the USB host; a crystal would be more appropriate.

[EDIT]
buhman
 
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Re: usbtinyisp design

by adafruit on Sat Aug 11, 2012 11:08 pm

hi,

we've noted your feedback that's relevant to your own build - not using our kit (and the other suggestions). we've asked you politely to stick to our customer service forum rules, this is our last request. it's a saturday night at 10pm ET, our team will review all of this as always and make any updates if they are needed :)

we appreciate your comments and concerns.

thanks again,
adafruit
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adafruit
 
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