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I have a drawer full of USB/RS232 adapters... is it possible to attach the Tx/Rx pins on the serial end of this cable to the Tx/Rx GPIO pins on the pi and have console access?

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EDIT: Bought this: http://www.amazon.com/gp/product/B00FEAMUOK/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1

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  • plug it in and type lsusb and show the display. You might need the drives
    – PhillyNJ
    Commented Jun 10, 2014 at 20:31
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    Probably not. RS232 on PCs is something like +/- 12V. A Pi uses 0 and 3.3V for its UART.
    – joan
    Commented Jun 10, 2014 at 20:37
  • Can you explain, where is the usb end connected. I guess you want to connect the rs232 usb end to another machine and the rs232 end to the pi. If so here is an idea, you say you have a draw full. Take out 2. Connect the rs232 ends together, using a null-modem, (2 to 3, 3 to 2, gnd to gnd, I think look it up). Then connect one usb to the py and one to the other machine.
    – ctrl-alt-delor
    Commented Jun 10, 2014 at 21:53
  • @joan these usb rs232 usually work at 5v. Check it, then add limiting resisters.
    – ctrl-alt-delor
    Commented Jun 10, 2014 at 21:55
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    RS-232-C is an old standard, which requires ±12V, although this was extended to ±25V. Very few modern implementations exceed ±5V and most are now unipolar, omitting the -ve swing. A USB adapter is unlikely to exceed 0-+5V range. The Pi would need to limit input to 3V, but is unlikely to meet the minimum send level of +3V so active level translation would be required for reliable operation.
    – Milliways
    Commented Jun 11, 2014 at 7:33

4 Answers 4

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No. The Raspberry Pi Tx/Rx GPIO pins are 3.3 volt logic. Standard RS-232 serial can be as high as 12-15 Volts. Connecting a standard RS-232 directly to the GPIO will probably damage the Raspberry Pi.

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So you have some computer running a terminal emulator, but that computer only has a USB serial port. You want to plug your converter cable into that USB port and connect the RX, TX and GND pins at the D-shell connector to the corresponding GPIO pin on your PI. ... and the answer is ...maybe. https://elinux.org/RPi_Serial_Connection

Check the voltages at the D-shell. These old converter cables typically output a 5 volt TTL signal at the D-shell. The signals at the D-shell connector are derived from the USB 5 volt power. These serial converters generally do not boost the voltage, but 5 volts is still enough to damage a PI's GPIO. You will need some kind of simple level shifter to interface the converter's 5V logic to the Pi's 3.3 V logic. https://elinux.org/RPi_GPIO_Interface_Circuits#Level_Shifters

If you build a level shifter, your idea can safely work. Of course, there is also the lazy man's method. https://www.adafruit.com/product/954

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type lsusb on your terminal you should see the device. Go to this link for details on how to use it.

http://elinux.org/RPi_Serial_Connection#Console_serial_parameters

you may need to install "screen" on the pi.

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You could use this to connect RX/TX from GPIO header to USB. http://www.ftdichip.com/Products/Cables/RPi.htm

It does not need any additional drivers, since support for the ftdi chips is already integrated into the kernel.

You may have to install some packages though to access the serialport, depending on your distro. Screen, minicom, microcom should all work.

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