Maybe I need to understand the bootloader auto-reset better.
I've got two Nanos operating on separate 5v power. They are connected only by a common ground and one Nano Tx pin is connected to the other's Rx pin. I have some keypad inputs on the transmitting nano that change its LCD display. Sometimes pressing a key on the transmitting nano (not when it's transmitting), the other nano resets. Other times, instead of reseting, the second nano goes off to La-La land.
When serial messages are being sent, the second nano behaves normally, with what appears to be 100% accuracy receiving and displaying the messages (temperatures, so there is no keypad action required in order to watch this process).
Second and maybe related issue: I am bothered by the fact that when Tx from one nano or mini is connected to the Rx of another, if the first device is powered, the power-on LED on the second device glows dimly, even with no power to that device. I've seen this repeatedly between many devices. It doesn't seem to harm either of them, but it bugs the poop out of me. Do I need a diode in the Tx line so that it can only pull the Rx pin low, but not be able to feed power to the second device? I don't see any notes about this except the usual 5v vs 3.3v warnings and the TTL vs +/-12v serial connections.
on edit: tried the diode, serial still works, but it also still resets/goes La-La.
Delta_G:
This post is useless without code or wiring diagram.
Let me be totally clear. Two wires. (1) Ground to ground. (2) Tx on one nano to Rx on the other. That's the wiring diagram. No capacitors, no resistors. If you need a schematic, in my opinion it wouldn't help you.
This is not a question about code. It is a question about hardware and the boot-reset that is triggered when uploading a sketch. For example, if the transmitting nano generates a small power dip when it changes the display on a 4x20 LCD, can the reduction in voltage due to the "dip" (and probably pretty small, since all its operations continue normally) do something on the Tx line that can reset the other nano?
It is obvious to me that there is a small but significant current draw via the Tx line by an unpowered Arduino that is connected to the powered Arduino via the Rx (and maybe the Tx) pin. You can put a diode in the Tx line, but that only isolates in one direction.
My next step is going to be to connect one nano to +5V and the other to RAW +9v, then the reverse, and see if that makes a difference.
Delta_G:
You said there was only two connections and then you mention an LCD.
Let me help you think about hardware. Two boxes, lots of stuff in each box. ONLY TWO WIRES AND 60' BETWEEN THEM. How does the Tx link reset the second nano? This is an electrical question that, I admit, requires some knowledge of the nuances of Arduino boards that are well known and do not require further explanation here.
If you don't have the expertise, experience, or familiarity with EMI or similar issues, eg, the occasional Arduino that is unusually susceptible to upset, that result in unexplained resets, I would suggest that you take your own advice and get off this topic.
Delta_G:
For what it’s worth I’ve got two nanos talking over Serial for months and I haven’t had any problem.
Just what I would expect, hence the post.
I assume that with 18,000+ posts you have helped many of us less experienced members. I appreciate that. However, your request for "sharing anything of the project" seems unjustified in this case and is raising my suspicions on whether there are motives that aren't obvious.
Does the problem change if, instead of connecting TX to RX directly, you use a low value resistor, say 1k ?
On the Receiver Nano, are you directly manipulating pin 0 ?
Is either Nano connected to a PC via a USB cable?
It also sounds like a length that could be unstable given its a simple one direction serial rather than a twisted pair bi directional with some form of handshake as per most serial connections.
Maybe it was the invitation to parasitic noise that has been described so far.
But without DETAILS such as wire type, sketch, schematic etc etc. those are simply guesswork on my part.
Might I strongly suggest those details be forthcoming.
They are integral to finding a solution.
Let me help you think about hardware. Two boxes, lots of stuff in each box. ONLY TWO WIRES AND 60' BETWEEN THEM. How does the Tx link reset the second nano? This is an electrical question that, I admit, requires some knowledge of the nuances of Arduino boards that are well known and do not require further explanation here.
Unknown baud rate that's one of many missing details.
Lots of stuff in each box, none of which we know about apart from an LCD.
Plastic or metal boxes ? dunno that either.
Grounding arrangements are another guess too.
Not picking on Dr.Q. here just pointing out a few of the things we do not know.