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Topic: Hacking into PIN0 and PIN1 aka UART (Read 484 times) previous topic - next topic

bkubicek

Hi!
I am the proud owner of a 3d-printer named Ultimaker. It is controlled by a arudino mega 2560, and is controlled from the host PC via a virtual com port.
I want to  build a thing that goes in between Arduino <> Mything  <>USB<> PC. It  buffers and modifies the bi-directional communication .
Mything might be an arduino, or just some atmega. Mything is actually an interactive control panel for the 3d printer.

So now the question: Can I use Rx/Tx aka Pin0 Pin1 on the arduino mega to communicate to Mything? Sending to mything with arduino TX->mything RX should work, I think. But how about the arduino rx? Is the usb/ttl converter leaving it floating while there is no signal recieved from usb, so that I can splice mything TX into it?

greetings, and thank you,
bernhard

retrolefty

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So now the question: Can I use Rx/Tx aka Pin0 Pin1 on the arduino mega to communicate to Mything? Sending to mything with arduino TX->mything RX should work, I think. But how about the arduino rx? Is the usb/ttl converter leaving it floating while there is no signal recieved from usb, so that I can splice mything TX into it?


Yes, if the serial converter chip (either 8u2 or FTDI) is idle and nothing is being sent from the PC to the arduino, then you can use the pins 0 and 1 externally.

PaulS

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Can I use Rx/Tx aka Pin0 Pin1 on the arduino mega to communicate to Mything? Sending to mything with arduino TX->mything RX should work, I think. But how about the arduino rx? Is the usb/ttl converter leaving it floating while there is no signal recieved from usb, so that I can splice mything TX into it?

Yes, you can use the RX/TX pins for communication. You could use any other pair of pins, though, using NewSoftSerial to simulate a serial port, so as to not interfere with the hardware serial port, leaving it free for debug use.

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It  buffers and modifies the bi-directional communication .

You don't have all that much space to buffer data.

What is mything going to be doing that the Arduino can't do?

bkubicek

I want to create a device for makerbots/repraps/ultimakers, that can interactively control them with or without host pc.
Because the firmware of the things is highly different, I need to hack in somewhere in between, to obtain maximum portability.
Ideally, Mything would be a usb slave for the PC, and a usb host for the 3d printer.
Mything might be an arduino, i don't know yet.
For buffering, I intend to use a sd card.

I would have expected that the RX pin would not float, because then the arduino might recieve random data?

retrolefty

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I would have expected that the RX pin would not float, because then the arduino might recieve random data?


When idle the 8u2 or ftdi send data (to arduino RX) is at a HIGH state and wired via a 1k ohm isolation resistor to the RX pin, so noise on the RX input pin should not be a problem.

Lefty

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