I have an Arduino UNO with an extension shield. The shield communicates with the UNO via serial communication over RX0/TX0. Now, it would be nice to use the normal USB/serial interface to the UNO in parallel, e.g. to monitor the communication between UNO and the shield. So it's like on the other end of the Arduino serial line there are two devices which can send to the Arduino via RX0 and receive from TX0.
I have done that without much thinking and it worked, i could see what the UNO sent to the shield, i.e. what appeared at TX0 (of course not what the shield sent to the UNO). Is this technically safe, or could it break something?
Is this technically safe, or could it break something?
As long as you just want to monitor what the Arduino sends to the shield, it's OK. As soon as you try to use that connection for debugging it will obviously break the Arduino-shield communication.
I also want to send data to the Arduino via USB, of course only when the other device is not sending. But what would happen if accidentally happened, could it physically destroy something?
I also want to send data to the Arduino via USB, of course only when the other device is not sending.
How would the Arduino know who sent the data?
But what would happen if accidentally happened, could it physically destroy something?
Theoretically this is possible but most probably the internal bypass diodes will catch the short circuit that might happen.
I definitely don't recommend to use such a setup. If you need more than the one serial interface the UNO offers, use a Mega2560 or something similar (the Leonardo might serve as well if just one hardware serial in addition to the debugging channel is necessary).