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Topic: Supply for handmade arduino (Read 1 time) previous topic - next topic

MarkT

And there are no 0.1uF decoupling caps on Vcc and AVcc .... Grrrr!
[ I won't respond to messages, use the forum please ]

CrossRoads

AREF is also connected to AVCC, instead of being independent - with its own 0.1uF cap.
No diode across the reset resistor either.
Bare minimum designs have certainly been drawn up better:
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

vasquo

What's the purpose of C3 on the reset pin?
I'm not familiar with that one.

CrossRoads

C3 lets DTR from a USB/Serial adapter perform an autoreset during serial downloads.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

SirNickity

Stupid question:  What's the diode across the reset pull-up do?  I know I've heard of that before, but I have no idea what problem it's meant to solve.

As for capacitors, I use Fairchild's recommendation.  Big(ish) electrolyitc caps on input and output side -- sized to provide adequate capacity per the application, but often 470uF on input, and 100uF on output.  Parallel ceramic caps on the input and output sides of the regulator -- 100nF each (though Fairchild recommends a 330nF on the input FWIW.)  Additional 100nF ceramics on Vcc pins of all ICs, as well as the AVcc of AVR chips.

None of these change the regulator's output voltage.  In fact, they're there so the voltage doesn't change with load.

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