USB Arduino failure to upload -- Solved ?

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westlake
 
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USB Arduino failure to upload -- Solved ?

Post by westlake »

I may have found the problem with the

You've got a significant circuit design error.

The reset pin is not clamped to less that 0.5 volts above the power supply.

When the DTR line goes high the reset pin is driven, through the 0.1 uF capacitor by 10's of mA, above the 5 V supply. It goes to almost 10 volts.

This has the chance of putting the AVR into high voltage program mode ( maybe ) ... effectively disabling it from further serial communication ...

OR more likely, it may also turn-on other parasitic structures within the AVR CMOS structure ... that can cause a whole host of internal malfunctions.

---------------

That 0.5 V spec applies at 20°C ... so it's less than 0.5 V at high temperature.

You need to add a schottky diode rated for at least 0.5 A from Reset to +Vcc to keep the over-voltage below 0.5 volts above the power supply.

On my board a 1N5817 clamps the voltage to about 0.25 V, A smaller signal schottky still allows the voltage to exceed 0.5 V


---------------

After I added the diode ... and recycled the power ... the USB-Boarduino board " as received software " started to work properly.

=================

AND there's another possibility that could be causing malfunction.

Several of the pins on the FTDI chip are not terminated.

I cannot tell from their data sheet whether we have any floating CMOS inputs or not.

And if so ... that could raise all kinds of unpredictable behavior.

PLEASE ... Someone at Adafruit ... check that possibility and let us know what you find.

adafruit
 
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Re: USB Arduino failure to upload -- Solved ?

Post by adafruit »

Thanks for the note - we'll check this out!

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