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Topic: please add a jumper to disable auto reset (Read 76702 times) previous topic - next topic


C4 in the linked schematic is controlling the auto reset.  Without it, it won't auto reset. Or you could try tiepie's solution of putting a larger value capacitor between gnd and reset.  



For the record, the latest versions of the Duemilanove don't have the solder pads with the trace between them.  Earlier ones do, the later ones don't.  Most compatibles and knock offs have the pads as per the early original boards.

In that case ive been ripped off many a time. Why not just re-instate that trace?


Why not just re-instate that trace?

Trust that the trace always exists or the auto-reset would not function. There just may not be an easy to see/roomy enough area to show where to cut. However once the trace is located it can either be cut or the series capacitor can be removed. I think the low ohm resistor temporarily inserted into the shield +5vdc and reset pins is the simplest way to go.



I think the low ohm resistor temporarily inserted into the shield +5vdc and reset pins is the simplest way to go.

I like tiepie's absorbing the ground pulse from the auto reset capacitor into a much bigger one charged to +5v, seems more refined somehow ;)


Jul 25, 2010, 11:23 pm Last Edit: Jul 25, 2010, 11:26 pm by madworm Reason: 1
It's quite strange that this _regression_ made it to the latest boards.

Granted, a switch/jumper would be much better, but why remove it. It's not like people got confused about it or it added cost to the board.
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the latest versions of the Duemilanove don't have the solder pads with the trace between them.

Huh.  I dislike it when open source hardware published designs get out-of-sync with the versions that are actually shipping (or even non-open-source designs with published schematics.)  On the other hand, it's pretty tough to keep in sync (you don't want to publish a new design for every minor manufacturing change), and the Freeduino designs seem to have suffered the same fate, so I guess I'll survive...


Thanks Lefty,

I will remove the C4 0.1uf ceramic capacitor connected to the reset tack switch.

So removing the C4 is the same as adding a switch with a resistor that is connected to a 9V source in the DTR part?



Removing the C4 capacitor completley disables auto reset, not quite sure how the 9v enters into the equation.  

The reset on the arduino is activated when the pin is brought LOW (0v) from its normal state held high (5v) by a 10k resistor.  What happens with the DTR is that the DTR is usually high (5v) and goes low when the serial port is initialised.  This change of state is 'transferred' via C4 to the reset pin which temporarily drops low before being brought high again by the pull up resistor and resetting the Arduino.  If C4 isn't there it doesn't happen and the arduino only resets by pressing the button. The workarounds to this autoreset revolve around keeping the reset pin High despite the best efforts of C4 to bring it low when DTR goes low.



Don't know if it has already been said in previous page, anyway here it is the solution for Arduino serial controlling from Windows XP in VBA (Visual Basic for Applications):

Connect your source to Microsoft Comm Control (MSCOMM32.OCX) , then:

Dim MSComm1 As Object

Sub ArduinoOpen()
   Set MSComm1 = CreateObject("MSCOMMLib.MSComm")
   MSComm1.Settings = "9600,n,8,1"
   MSComm1.CommPort = 4
   MSComm1.InBufferCount = 0
   MSComm1.DTREnable = False
   MSComm1.PortOpen = True
     If Err Then
        MsgBox "COM" & MSComm1.CommPort & ": not opened, Sorry!"
        Exit Sub
     End If
End Sub

Sub ArduinoClose()
   MSComm1.PortOpen = False
   Set MSComm1 = Nothing
End Sub

Tested on ArduinoUno

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