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I have recently designed a shield to my Arduino Duemilanove, which has 8 LEDs, on the digital GPIO, from 0 to 7, but it won't program with the shield on because the voltage drop is too much on the RX and TX lines. My question is: can I have a LED on the TX/RX line with a minimum resistor value that allows me to program the Arduino?

Glorfindel
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Electropepper
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1 Answers1

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I just found this reference (using ICSP for output as well as programming -- essentially the same thing), and it suggests a 4.7kOhm.

I didn't have a 4.7k handy, and used a 15k instead and it works.

In my scenario, I have run a sketch with a polarized buzzer connected between RX (digital 0) and GND. When connected directly (with no resistor) the sketch fails to load (but the buzzer works as expected).

If I put the resistor in series with it, the sketch uploads without fail.

You also probably realise, but mentioning for clarity/completeness, you will lose all serial port functionality for debugging purposes and won't be able to use Serial.[anything]. Make sure to not even initialise the port.

Madivad
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