prepare

Preparing a Arduino Uno for reprogramming by using the high voltage (12 volt) parallel method. You need to cut up to three tracks on the UNO PCB so that the 12 volt voltage that you apply to the reset pin does not feedback on to the 5 volt supply or back onto your USB chip.

UNO R3 have a resistor and diode near the six pin ISCP plug that bleads excess voltage from the reset line on to the 5 volt circuit. You need to cut that track. If there are two ISCP plugs on your board then you will also have another resistor and diode near that second plug. You will need to cut the track from those too. Earlier versions of the UNO PCB do not have those resistors and diodes. When you cut the reset tracks you want to try and keep the track to the RES pin on the side connector. You'll need that for connecting your 12 volts. There is a capacitor near the USB chip that allows it to pull down the reset line. You need to cut the PCB track to that. Once you have finished programming you can solder a wire across the cut or replace the track with piece of wire.

You will need to solder a wire on to the XTAL1 track. This can be done by soldering on to the bottom connector of the crystal.

Here are some photos of a couple of my PCBs. All these clone type boards differ slightly.

Wire soldered on to XTAL1 track.

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Last updated 29 January 2017.