You deploy a sensor node—perhaps a temperature monitor pushing JSON to an MQTT broker. It runs flawlessly on your workbench for an hour. You deploy it to the field. 24 hours later, the device hangs, reboots unexpectedly, or stops transmitting. You hit the physical reset button, and it works perfectly again... for another 24 hours. This is not a hardware fault. It is almost certainly a memory management issue caused by the misuse of the standard Arduino String class. While convenient, the String object is a dangerous abstraction in embedded environments with limited SRAM (like the ATmega328P's 2KB). The Root Cause: Heap Fragmentation To understand why your device crashes, you must understand how memory is mapped on an AVR microcontroller. The SRAM is divided primarily into two dynamic regions: The Stack: Grows downward. Stores local variables, function parameters, and return addresses. The Heap: Grows upward. Stores dynamic memory allocated via...
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