Go Down

Topic: Regression between uno and uno R2 VALIDATED. HARDWARE PROBLEM CONFIRMED (Read 27 times) previous topic - next topic

Boz



Coding Badly

Quote
This prevents the +10vdc pulse from the auto-reset cap from causing the problem stated in this thread ... consistently make the 328 chip power up into some kind of 'locked-up' condition


Quote
Enter Programming Mode ... 3. Wait 20 - 60 ?s, and apply 11.5 - 12.5V to RESET.


I suspect the "locked-up" condition is parallel programming mode.  I wonder if that's how the bootloader gets erased?

retrolefty


Quote
This prevents the +10vdc pulse from the auto-reset cap from causing the problem stated in this thread ... consistently make the 328 chip power up into some kind of 'locked-up' condition


Quote
Enter Programming Mode ... 3. Wait 20 - 60 ?s, and apply 11.5 - 12.5V to RESET.


I suspect the "locked-up" condition is parallel programming mode.  I wonder if that's how the bootloader gets erased?



As good a theory as any. I always wondered how bootloaders got corrupted, because as far as I know there is no way a arduino sketch can blow up a bootloader?
Lefty


tim7


Quote
Could someone describe the diode fix, can someone participating sum up?


Wiring a diode from the reset pin to +5vdc (cathode lead to +5v) clamps any voltage higher then +5vdc going to the reset pin. This prevents the +10vdc pulse from the auto-reset cap from causing the problem stated in this thread. It's treating the symptom rather then the cause, but is simple and effective.


I just came across this thread after acquiring an Uno R2.  The coupling capacitor used for the auto-reset feature kind of bugs me:  disabling auto-reset (as required by certain applications) involves overloading - albeit briefly - the the pin on the ATmega8U2.  As does the proposed diode-clamp.

This situation calls for a proper solution.  Switching the reset pin via a transistor entails no risk of voltage spikes, doesn't impede high-voltage programming, and can be disabled with a simple short.  Excuse the scribble:



The disadvantage is that the logic of the auto-reset signal is inverted (high -> reset).  Of course this can be corrected in the 8U2 firmware, but it's not a solution for boards which use external serial interfaces.  These boards could use a second transistor to invert the auto-reset signal.  Any thoughts?

Go Up