I am using the ProMicro Leonardo on a project.
I picked it because it has two UARTs and my primary objective was to receive loads of RS232 Binary Data, process and act on it by operating relays and LEDs.
It seems to be doing the job just fine but I am occasionally having a problem.
I receive RS232 (the real thing) with a MAX232. The data is then converted to TTL levels and connected to the RXI pin on my Arduino 2nd serial port. The baud rate is 38.4k baud.
The system never does anything but take in the serial data, process it, then loop.
I never do a print.serial or any other serial output command.
My problem is that after a while (could be several days), the MAX232 will suddenly overheat. It gets so hot it will burn my finger. Then it will often die. I replace it and I am back in operation again.
I have a couple different batches of MAX232 and I have tried to make sure I have tried different units. Same goes for the ProMicro.
I am using a custom PCB and the TXO pin is connected to the MAX232 transceiver as well, even though I never use it in the sketch.
The unused TTL input on the MAX232 is grounded (there are 2 drivers on that chip) and the unused RS232 input is open. I have been using MAX232 devices for decades and never seen this problem and never worried about terminating unused RS232 inputs. The schematic for the chip shows a 5K termination internal on the chip.
So I am wondering if I need to do something with the ProMicro serial1 output, even though I am not using it. Could the TX pin on the Arduino be going into oscillation or doing something it shouldn't that is messing with the unused RS232 converter?
Is it even possible to override the serial1.begin( baudrate ) function and set the TX pin to something else?
What about just sending some data now and then to make sure the TX pin is in a known state?
You people on this forum are really smart and come from such a wide background. I am hoping one of you has an idea for me.
Currently, I pulled the unused TTL input pin out of the MAX232 dip socket so its disconnected from the ProMicro. Lets see if I have the same problem. Its been running for a couple of days now with no problem, however, sometime it takes days to malfunction. My system runs 24/7/365