UART connections on Rpi GPIO

Hi, does anyone know if the UART tx and rx pins can be used to connect usb devices directli to the GPIO connection of the Rpi?

Or can it be used to connect the pin0 and pin1 of the arduino as a direct serial link to the arduino?.

shabaz over 12 years ago

Hi Omar,

As I understand, the traditional Arduino uses 5V logic signals (whereas the Arduino Due uses 3.3V I believe), and the RPI uses 3.3V levels. You could connect the UART pins together across the two boards, but only if they are using the same logic levels. Otherwise, you need some level converter, something like this, powered from 3.3V. (It is a quad NAND gate ic, you can tie the inputs together per gate, and tie the unused gate inputs to 0V). It is surface mount, but is the large SOIC package which is easy to solder.

EDIT: ugh, sorry, you need something like this, not NAND, which will invert your logic (unless you chain them). I'm just so used to using NAND gates for everything..
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guzunty over 12 years ago

Hi Omar,

USB protocols are much more sophisticated than simple serial links. They have a hardware and a software component, and so you cannot connect the rx/tx lines directly to USB.

What people do instead is to use something like this : http://www.adafruit.com/products/954

As Shabaz said, you can only connect Arduino's directly to the Pi serial lines if the Arduino is running at 3.3v. This is possible, there's one on the Gertboard. However, you then can't run the Arduino at its full speed. For that reason, most off the shelf Arduinos are 5v based, which means you must use an interface chip. This one can do much more than interfacing to Arduinos: https://github.com/Guzunty/Pi/wiki. Disclosure: I curate this site.

HTH,

Derek
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Former Member over 12 years ago in reply to guzunty

Yes: http://www.panu.it/raspand232/

Alberto
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mgt6910 over 12 years ago in reply to Former Member

My Firefox Browser has informed me that the certificates of this site can not be trusted. I'll pass on that then, thanks.
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Former Member over 12 years ago in reply to mgt6910

I used the wrong protocol, post corrected!
TX.

Alberto
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