2
\$\begingroup\$

I was constructing my own arduino duemilanove, I noticed there was 1K resistor wired in series with the txd and rxd. Why does it need them? It works for me without them.

\$\endgroup\$
1
  • \$\begingroup\$ Be careful how you say it is wired. The 1K resistors on the Duemilanove are between the TX/RX pins and the FTDI chip. I think the reason, as Leon says below, is to prevent bad sketches from breaking the FTDI chip. \$\endgroup\$
    – ryantm
    Oct 9, 2011 at 4:44

2 Answers 2

7
\$\begingroup\$

A programming error could cause two outputs to be connected together, which could damage the devices. Those resistors will prevent excessive current from flowing if that happened. The only one that is really necessary is the one on RxD as TxD is connected to an input.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ a programming error, or as is often the case, just trying to connect two devices using a patchwork of adapters, gender changers, and what-not, b/c you don't have a single cable that will do it in one jump. \$\endgroup\$
    – JustJeff
    Oct 9, 2011 at 2:50
1
\$\begingroup\$

This may be required whenever you use a shield that uses TX/RX (like a XBEE shield). You can't program the atmega chip from FTDI when the Shield is in place, because there are 3 devices connected to TX/RX.

A problem would occur when the atmega is listening (RX) , Zigbee is outputting '1' (5V) and FTDI is outputting '0' (0V). The zigbee connects 5V to the RX net, FTDI connects GND to the RX net. 5V connected to 0V is smoke. A 1k resistor prevents that from happening, as only a limited amount of current will flow.

\$\endgroup\$
0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.