Background
L3Harris offers a line of incredibly tough voice radios for firefighters; the XL Extreme. They represent a never-before-seen level of ruggedness: impervious to high temperatures, submersion, and extreme impacts.
This speaker-microphone, designed and engineered by Porticos, highlights some of the expertise that Porticos brings to handheld electronics.
Challenges
The XL Extreme Speaker Mic, or ESM, taps into the critical controls and features of their fire radio (also engineered by Porticos) with commensurate high standards for audio quality. Porticos created an architecture to translate the raw output from a MEMS microphone to a signal that could be packaged for USB streaming. Digital signal processing (DSP) techniques were employed to achieve a specific frequency response. The audio conversion, processing, and packaging challenged the limits of available processor resources, so Porticos optimized signal processing tasks to work within those limitations.
Generic flex circuit.The controls on the ESM are densely packaged, so Porticos made extensive use of flexible printed circuits (FPC). FPCs simplified assembly, reduced the volume of wires inside the device, and allowed sensitive signals to be shielded without the use of bulky shielded wire.
Because the ESM is powered by a host radio, power consumption must be strictly limited. Porticos developed a sophisticated calculator that estimated the power consumed based on usage scenarios, measured power consumption, and projected dynamic component efficiencies.
A validation test plan was developed that included applicable National Fire Protection Association (NFPA) testing, tests devised by Porticos, and tests specified by L3Harris. One of the most challenging tests requires operation in a 260°C (500°F) environment for five minutes. Some electronic components must be operated above the rated maximum temperature during that test, so the ESM was tested extensively to validate performance and reliability. Porticos generated interface hardware and test applications to simulate a host radio to facilitate that validation effort.
Outcomes
The XL Extreme Speaker Microphone is the first and only device of its kind to be fully compliant with NFPA 1802. Porticos engineers met or exceeded all requirements for audio quality, size, ruggedness, and battery life.
