<![CDATA[Cardiac auscultation training traditionally relies on passive manikins or direct patient contact, both of which limit exposure to varied heart sound patterns at multiple anatomical points and remain costly to acquire and maintain. This study investigated the feasibility of the Message Queuing Telemetry Transport (MQTT) protocol, combined with Network Time Protocol (NTP) based timestamp synchronization, for coordinating audio playback across distributed low-cost microcontroller nodes as a first step toward a distributed cardiac auscultation simulator. A prototype consisting of two ESP32 microcontrollers, each driving two independent I2S audio channels through MAX98357A amplifiers, was connected to a Mosquitto MQTT broker running on a laptop acting as a temporary central controller. Three experimental scenarios were conducted: baseline synchronized playback on a single channel per node, synchronized playback on a second channel per node, and simultaneous two-channel playback within a single node. Across 25 to 30 valid trials per scenario, median command latency ranged from 44.5 to 124 milliseconds, and median inter-node synchronization error ranged from 243.5 to 369 milliseconds. Simultaneous two-channel playback within one node revealed a median 9.7-second delay between channels, attributed to blocking audio playback in the current firmware. These results demonstrate that MQTT-based synchronization is technically feasible on low-cost hardware, though the achieved accuracy falls short of a ±50 millisecond target, indicating specific firmware optimizations needed to improve synchronization precision.]]>
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