Use a broken arduino as USB to serial module

Hello,

I needed more ram for one of my projects and I built an "Arduino" with the chip ATMEGA1284, which works fine; the problem is that in the kit I bought the module for the USB connection was not included. Can I use an old broken Arduino Mega as a "module" to connect my ATMEGA1284 to the PC? I don't want to just program it using an Arduino as ISP, i'm interested in connecting it to the PC and beeing able to send and receive data via serial connection.

Thanks

Assuming the broken Mega's serial adapter portion is working - but on official boards (eg, with 16u2 serial adapter), the serial adapter is the part most susceptible to damage - so it's likely that the part you want to use is what's broken.

Why not spend $1.65 on one of these lovely serial adapters? (no specific endorsement of that vendor - but that's the model you want, the ones with the little voltage switch. Other vendors sell identical modules for similar prices) http://www.ebay.com/itm/191146797242

I agree with DrAzzy on both counts but if you do want to try this you should be aware of something counterintuitive: The RX0 pin on the Mega is connected to the TX pin on the USB-serial chip and the TX0 pin is connected to the RX pin on the USB-serial chip. Normally you should always connect RX-TX and TX-RX but in this case you would need to connect RX0 on the Mega to RX on the ATmega1284 and TX0 to TX on the ATmega1284 since that actually ends up being a RX-TX, TX-RX connection between the USB-serial chip and the ATmega1284.

I can't say how the ATmega2560 on the Mega board might interfere since I don't know how it's broken. You might try holding it in reset if you have problems.