[sdiy] Arduino schem - diode in series with R at reset pin?

[Ullrich Peter]

Yes, ist clamping to the 5V rail but limiting to 5V is not the cause its here...
It's here to discharge reset capacitors over the 5V rail in case of a short power fail so that a proper reset can be generated.

As the 5V go down at power off the capacitor will be discharged so that the reset pin goes down to the level of the VCC plus the voltage drop.

Ciao
Peter

-----Ursprüngliche Nachricht-----
Von: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-bounces at dropmix.xs4all.nl] Im Auftrag von Gordonjcp
Gesendet: Donnerstag, 23. April 2015 16:38
An: synth-diy at dropmix.xs4all.nl
Betreff: Re: [sdiy] Arduino schem - diode in series with R at reset pin?

On Thu, Apr 23, 2015 at 07:27:34AM -0700, Justin Owen wrote:
> Hello,
> 
> http://i.stack.imgur.com/cPCB4.png
> 
> Some of the Arduino schematics have a diode in parallel with the normal R to VRef on the Reset Pin (Pin 1 in the above link).
> 
> Can anyone explain what the diode is doing and why it only seems to be on Arduino schems?
> 
> FYI, I'm looking specifically at using the Atmega 328P in a non-Arduino, stand-alone circuit.
> 

It clamps external voltages on the reset pin to the 5V rail.

-- 
Gordonjcp MM0YEQ

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