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i don't which voltage you use for triggering the POR chip is that important. all that is important is that you reset the microcontroller after a reasonable delay after power is applied. of course you need a voltage that matches the threshold of the device. they come in a few different thresholds to work with 3.3 5 and maybe other voltages. i use a fairly large capacitor for a long delay just to be sure. it has worked absolutely reliable. i used a dip version but i am sure you can get surface mount if space is a problem and use a tantalum cap if there is no room for an electrolytic for the timing cap. make sure the POR chip never sees sense voltage without its power supply connected. i made a shield with some of those crappy thin pin stackable headers that came with the dev shield and a bad connection to 3.3 volts killed the POR chip. not much of a loss but a waste of time figuring out why it didn't work. since then i found some better square pin stackable headers.

it seems to me that this startup problem is a bug with the DUE. are there any configuration options that might fix this in the microcontroller instead of forcing us to add POR chips?

What about a 12v zener diode so it doesn't send voltage till it hits the 12 volt breakdown voltage?  That's the first thing I would try if I was getting brown-outs at startup.

Tim
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Arduino - Teensy - Raspberry Pi
My libraries: NewPing - LCDBitmap - toneAC - NewTone - TimerFreeTone

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What about a 12v zener diode so it doesn't send voltage till it hits the 12 volt breakdown voltage?  That's the first thing I would try if I was getting brown-outs at startup.

Hi,
which kind of connection do you suggest? I know the classic Zener scheme with resistor in series and Zener between Vcc and hearth. But this kind of connection only cuts Voltage when it goes above the zener limit (for what I understand).

Thanks in advance,
Luca
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Hello, I have also the same problem.
Every time I start up, the DUE hangs and I must press the RESET button...

I use the USB-Power on the programming port.

paulinchen
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good to hear i am not the only one having this problem. i did fix it with the power on reset chip but would really like to know if there is a fix by configuring the brownout detector on the microcontroller. this is the only microcontroller board i have had this problem with.
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What about a 12v zener diode so it doesn't send voltage till it hits the 12 volt breakdown voltage?  That's the first thing I would try if I was getting brown-outs at startup.

Hi,
which kind of connection do you suggest? I know the classic Zener scheme with resistor in series and Zener between Vcc and hearth. But this kind of connection only cuts Voltage when it goes above the zener limit (for what I understand).

Thanks in advance,
Luca

For the life of me I can't figure it out now.  I know at one time I made an undervoltage lockout circuit based on a zener, NPN, and potentimeter.  Basically, with the correct breakdown voltage zener and the potentimeter, you could dial-in an undervoltage lockout.  It worked really well with a voltage source like 12 volts when you wanted to output a much lower voltage like 3.3 or 5 volts.  The voltage was very low till the input voltage got very close to 12 volts, then went up very fast to the 3.3 or 5 volts.  It wasn't like a switch, but created a very steep angle which worked for my situation.  But, maybe the Due is even more quirky.

Tim
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Arduino - Teensy - Raspberry Pi
My libraries: NewPing - LCDBitmap - toneAC - NewTone - TimerFreeTone

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