I'm trying to program a Mega 2560 with an external FTDI USB-to-serial adapter (i.e. not using the onboard USB port). I need this because the Arduino is about 20m away from the controlling PC.
When connecting RX, TX, VIN and GND from the adapter to the Arduino, I can send/receive data through the serial connection. As soon as I connect DTR to Reset, the serial connection stops working. After adding a 0.1µF capacitor between DTR and Reset, communication works again. Programming the Arduino does not, however. I always get the following message during upload:
Binary sketch size: 3,960 bytes (of a 258,048 byte maximum) avrdude: stk500v2_ReceiveMessage(): timeout ... Repeated 5 times ... avrdude: stk500v2_getsync(): timeout communicating with programmer
The adapter works fine when uploading to an Arduino Pro Mini, so I assume something in the Mega's onboard USB-to-serial part is interfering here.
Any ideas what I could do to make this work? Thanks!