Analog Angle Article

Innovative IC can’t trap lightning, but can let you know it’s coming

Unterpremstaetten, Austria—No need to tell this audience of the damage which lightning does to systems, circuits, and people. While good design practices, carefully placed suppression devices, and use of common sense by people can help minimize the damage, it would still be very useful to know when lightning is approaching and how far away it is.

To date, this has required relatively large, costly box-like instruments, but austriamicrosystems plans to change the situation radically with their AS3935 Franklin Lighting Sensor IC (named for Benjamin Franklin and his lightning experiments, of course), which they say is the first IC to perform this function. This tiny, low-power component, supported by a few small passives and a microcontroller for management and user interface, will enable lightning-detector key fobs, personal and portable warning instruments (GPS, fish finders, golf accessories), plus larger installations in networks, smart grids, and power systems.

The AS3935 Franklin Lighting Sensor IC from austriamicrosystems

uses an analog front end plus embedded algorithms

to sense the approach of lighting and the distance .

Unlike simplistic detectors which suffer from false alarms, the device uses a magnetic-field sensing coil as part of its RF receiver to detect the electrical emissions from lighting up to 40 km away down to 1 km. It assesses the distance not by signal strength alone but by analysis of the waveform itself using proprietary, integrated algorithms, based on standard meteorological survey patterns and data. As a consequence, it is not “fooled” by local disturbances such as microwave ovens, nearby motors, or similar transient sources, noted Johnsy Varghese, marketing manager, which soon makes people turn off any warnings (literally and figuratively).

[An aside : one of the nicest “do-it-yourself” projects for novice electronic hobbyists appeared in April 2002 QST (amateur radio), “A Lightning Detector for the Shack,” (sorry, not online for non-subscribers). It uses four low-end transistors, some non-critical passive components, a 2.5V flashlight bulb, and 3V supply, and has no layout challenges. However, it is susceptible to false alarms, since it has no intelligent signal-processing algorithms; it is an all-analog circuit.]

The 4× 4 mm, 2.4 to 5.5V AS3935 is a power miser, too, with drain of just 60 µA in listening mode (where it will be most of the time). It needs seven passive components needed, and has I2 C and SPI ports for interface to the support microcontroller (MCU)—all signal-analysis algorithms are embed within the AS3935 and do not require any processing effort by the low-end MCU. Further, an automatic antenna-tuning mode reduces the tolerance constraints on the front end components and eases manufacturing concerns.

Within the AS3935, the output of the analog signal-conditioning circuitry

is analyzed by integrated waveform-analysis algorithms,

based on standard models and data.

Products such as this, which measure unusual physical occurrences, always raise the question: “so, how do you know it actually does what you claim it does?” In this case, the vendor has done field trials in Finland and at the Florida Institute of Technology (Florida Tech), one of the world's leading centers for lighting research, and tests are now underway in South Africa. Field data was compared to data from the National Lightning Detection Network, and has been designed and tested for both cloud-to-ground and cloud-to-cloud lightning, as well (many existing instruments only detect the former).

Pricing, support, and availability : the AS3935, in a 16-lead MLPQ package, is $3.55 (1,000 pieces) and is sampling now.An evaluation kit consisting of an evaluation module, a lightning-emulation unit (you do have to have that, right?), and a thumb drive with GUI, and hardware and software design files, is also available.

For more information : Go to

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