Ramps board USB port is dead -- any way to use RX/TX and FTDI?

Hey guys,

I bought a really cheap clone board that I'm kind of stuck with now. I can program it using ICSP, and it seems to work alright, but as far as I can tell the AT Mega 16u2 is completely bricked and either -- can't be flashed -- or the ICSP header isn't wired up to it properly -- or something.

I'm wondering, are the Arduino's RX / TX pins (the ones it uses for USB serial) exposed on the pin header somewhere? -- are they just TTL 5v? -- And can I just hook up RX, TX, and GND on an FTDI board? Will that work? Or will I fry something else? -- Alternately, is it possible to just configure Marlin to use different RX/TX pins that are exposed? What do you think?

Also, ultimately I plan on grabbing a Raspberry PI 2 and running Octoprint -- I know the R-PI has its own GPIO pins, is it possible to just use some of those directly like a TTL serial port and avoid connecting to USB all together?

Thanks!

Edited 1 time(s). Last edit at 07/03/2015 03:59AM by BrainSlugs83.

Fooling around with pins 0 and 1 with various FTDI boards, and also, powering the device from inappropriate voltage sources, and lots of other ridiculous hair-pulling shenanigans later, and suddenly my 16u2 started working and like, showing up in the device manager and stuff. -- I reuploaded the 16u2 firmware in the hopes that this doesn't ever happen again, 'cause man that was awful.

You can read more about it on the Arduino Forums here: [forum.arduino.cc]

I am still interested, from a (probably) hypothetical perspective though: if anyone knows how to get Marlin (or other firmwares) to use an alternate serial port on the Arduino -- and/or -- if that serial port can connect directly to an R-PI's GPIO (instead of wasting a USB port), I'm all ears!


Thanks & Woot!

Edited 2 time(s). Last edit at 07/03/2015 05:42AM by BrainSlugs83.

TX/RX are just TTL 5v they are broken out on the mega pins labled TX0 RX0

They also go threw vias you could tap into, or pull the AT Mega 16u2 and use its pins, or tap in to resitors RN4A and RN4B

There are 4 serial ports. The other serial pins are used on endstop and AUX4 (LCD)
I have moved endstops to spare pins before to get access to other serial ports.

using a ftdi will work on other serial ports but.. with cavets

The 16u2 is also responsable for resetting the mega into boot loader mode for reprogramming over usb/serial (serial DTR line low reboots board)
Also the boot loader is hard coded for serial 0...

Marlin is easy to change it to use annother serial port. just edit [github.com] but you also have to move the conflicting pins off of the serial port pins.

If it was me, I would pull the mega 16u2 and wire in the ftdi into where it came from, incuiding the DTR line
see cct [arduino-info.wikispaces.com]

re raspbury pi.. I know its 3.3v ttl.. you so would have to drop the voltage from the mega threw a resitor so the pi only gets 3v.. eg [blog.oscarliang.net]

Edited 4 time(s). Last edit at 07/03/2015 06:05AM by Dust.

Nice! Thanks man! :-)

I had the same thing here man, had one of my end stops wired wrong and USB stopped working. I was fooling around going to do what you are talking about doing and happened to notice it just started working again. I wonder how this happens?

It still goes out occasionally, but a full power off with USB cable out seems to take care of this. I got another RAMPS and mega on the way. Not going to mess with it and risk it going down in the middle of a six hour print.