Last modified 6 years ago Last modified on 07/29/12 20:12:14

AS3935 Franklin lightning detector demo board

A demo board was developed to evaluate AS3935 Franklin lightning detector IC by AMS. Datasheet is available upon request from them, please note that datasheet may still contain a few errors.


Developed by: Musti

Demo board using MSP430G2331

The goal of the development board is to provide a cheap simple setup for testing AS3935 and that can be used as a DIY solution as well. It uses the old version of Texas Instruments MSP430 Launchpad using MSP430G2331. A more advanced version of the demo board is under construction, it will be compatible with the new Launchpad using MSP430G2553.

AS3935 Franklin lightning detector

AS3935 is an integrated lightning detector using an RCL antenna tuned to 500kHz to detect RF signature of a lightning strike, determine the distance of it from the detector and an arbitrary measure of strike power.

500kHz antenna design

MF - Medium frequency detection generally requires a very large antenna, however a small footprint antenna can be created using a tuned RLC antenna - magnetic loop antenna, where the inductor is ideally a single layer coil with a magnetic core.

Datasheet specifies Q factor of the antenna to be about 15, tuned to 500kHz with 3.5% accuracy. There is not a great choice of transponder inductors that suit this requirement. For the purpose of demo board, Coilcraft 1812LS-124XJLB 120uH, Q=33@790Hz is used, although not ideal. For a paralell RLC circuit also a 680pF (+120pF programmable + parasite capacitance 20pF) capacitor and a 10kOhm resistor are required.

A more appropriate antenna would be using Coilcraft MA5532-AE 100uH inductor, however it is a subject of the manufacturers lead time and was not used just yet. Capacitor for this setup is 1nF and 10kOhm resistor.

Circuit design

The circuit is designed to be a simple module with a minimal number of elements and a tabbed antenna mounting, allowing it to be extended outside metal enclosures. Demo board is a standalone circuit with an I2C connector containing power lines as well.


AS3935 library

A C library of functions has been developed, allowing simple interfacing of AS3935 IC via I2C module. It is definitely the most efficient implementation, but should be very transparent for demonstration and debugging purposes.

Source code is available on GitHub msp430-AS3935test-G2331.

Demo board using MSP430G2553

An improved version of the demo board utilizes a more capable MSP430G2553 microcontroller including USART - dedicated hardware uart interface, enablin the use of baud 115200. AS3935 library is improved with automatic tuning methods utilizing a frequency counter.

Frequency counter

Frequency counter module #893 is used to measure the frequency of the oscillator outputs on AS3935 displaying its clocks, enabling the tuning of RLC antenna with internal programmable capacitors 0-120pF in 8pF steps.

Standalone AS3935 circuit

The circuit is I2C interfacable, all design comments from above are incorporated. Schematic and PCB and gerber files are available.