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Support Forum » DB9 connector

December 28, 2011
by DS1000
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Hello, I'm having a great time with my nerdkit. I am wondering if I design a pcb and wish to use the serial port on my PC directly rather than a usb adaptor, which pins in the db9 connector on the circuit board would I need to hook up to the Atmega 168? thanks

December 28, 2011
by Rick_S
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If you use a true serial port, you will need to use a serial level converter. This can be a MAX232 IC or even something as simple as a couple transistors. The TTL uart on the micro uses an inverted protocol so even if the voltage levels were ok, it would not work. If you search ebay, you can find premade boards with a MAX232 for not a lot. I think I got one for around $5.

December 29, 2011
by DS1000
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Thank you Rick_S for the very fast reply. I will look in to the MAX 232. One of the reasons I would like to to this is that I am concerned about leakage through the yellow line in the USB-RS232 converter supplied by Nerdkits. Would you happen to know if using a full RS232 cable through DB9 connectors (and a MAX232) will eliminate this issue?

thanks

December 29, 2011
by Rick_S
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There is no issue to my knowledge using a max232 circuit. Also, if you want to go usb, you can get an interface based on the FTDI chipset such as the FT232 that is commonly on arduino's. You can get these USB to TTL serial interfaces on ebay or sparkfun electronics as well as several other sources.

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