Skip to content

Instantly share code, notes, and snippets.

What would you like to do?
AS3935 Arduino code example
____ __ ____ ___ ____ ____ __ __ _ ____ __
( __)( ) ( __)/ __)(_ _)( _ \ / \ ( ( \(__ ) / _\
) _) / (_/\ ) _)( (__ )( ) /( O )/ / / _/ / \
(____)\____/(____)\___) (__) (__\_) \__/ \_)__)(____)\_/\_/
Project name: AS3935 lightning detection using Arduino Uno
Project page:
Description : Demo code for AS3935 lightning sensor
/* This Arduino sketch requires the AS3935 library from
Based on the original library and code by:
LightningDetector.pde - AS3935 Franklin Lightning Sensor™ IC by AMS library demo code
Copyright (c) 2012 Raivis Rengelis (raivis [at] All rights reserved.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 3 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
#include <SPI.h>
#include <AS3935.h>
void printAS3935Registers();
// Function prototype that provides SPI transfer and is passed to
// AS3935 to be used from within library, it is defined later in main sketch.
// That is up to user to deal with specific implementation of SPI
// Note that AS3935 library requires this function to have exactly this signature
// and it can not be member function of any C++ class, which happens
// to be almost any Arduino library
// Please make sure your implementation of choice does not deal with CS pin,
// library takes care about it on it's own
byte SPItransfer(byte sendByte);
// tunecap is needed to display the calibration register value
int tunecap;
// Iterrupt handler for AS3935 irqs
// and flag variable that indicates interrupt has been triggered
// Variables that get changed in interrupt routines need to be declared volatile
// otherwise compiler can optimize them away, assuming they never get changed
void AS3935Irq();
// volatile int AS3935IrqTriggered; - not needed anymore
// First parameter - SPI transfer function, second - Arduino pin used for CS
// and finally third argument - Arduino pin used for IRQ
// It is good idea to chose pin that has interrupts attached, that way one can use
// attachInterrupt in sketch to detect interrupt
// Library internally polls this pin when doing calibration, so being an interrupt pin
// is not a requirement
AS3935 AS3935(SPItransfer,10,2); //change to AS3935(SPITransfer,9,3) if using slot #2
// AS3935 AS3935(SPItransfer,77,26); //if using Flip & Click socket A
void setup()
// first begin, then set parameters
// NB! chip uses SPI MODE1
// NB! max SPI clock speed that chip supports is 2MHz,
// but never use 500kHz, because that will cause interference
// to lightning detection circuit
// and chip is MSB first
// reset all internal register values to defaults
// and run calibration
// if lightning detector can not tune tank circuit to required tolerance,
// calibration function will return false
Serial.println("Tuning out of range, check your wiring, your sensor and make sure physics laws have not changed!");
// now we print the value in the calibration register TUN_CAP
// it is in the range 0 - 15
Serial.print("Tuning cap register is ");
// since this is demo code, we just go on minding our own business and ignore the fact that someone divided by zero
// first let's turn on disturber indication and print some register values from AS3935
// tell AS3935 we are indoors, for outdoors use setOutdoors() function
// AS3935.setOutdoors();
// turn on indication of distrubers, once you have AS3935 all tuned, you can turn those off with disableDisturbers()
// AS3935IrqTriggered = 0;
// Using interrupts means you do not have to check for pin being set continiously, chip does that for you and
// notifies your code
// demo is written and tested on ChipKit MAX32, irq pin is connected to max32 pin 2, that corresponds to interrupt 1
// look up what pins can be used as interrupts on your specific board and how pins map to int numbers
// ChipKit Max32 - irq connected to pin 2, or Arduino with irq connected to pin 3
// Uncomment the next line if using slot #2 of the Arduino mikroBUS adapter
// attachInterrupt(1,AS3935Irq,RISING);
// uncomment line below and comment out line above for Arduino Mega 2560, irq still connected to pin 2
// attachInterrupt(digitalPinToInterrupt(26),AS3935Irq,RISING); // if using Flip & Click socket A
void loop()
// here we go into loop checking if interrupt has been triggered, which kind of defeats
// the whole purpose of interrupts, but in real life you could put your chip to sleep
// and lower power consumption or do other nifty things
// I prefer to move this code inside the interrupt routine itself
// Here I leave only some code to display "Waiting..." so I know everything works
void printAS3935Registers()
int noiseFloor = AS3935.getNoiseFloor();
int spikeRejection = AS3935.getSpikeRejection();
int watchdogThreshold = AS3935.getWatchdogThreshold();
Serial.print("Noise floor is: ");
Serial.print("Spike rejection is: ");
Serial.print("Watchdog threshold is: ");
// this is implementation of SPI transfer that gets passed to AS3935
// you can (hopefully) wrap any SPI implementation in this
byte SPItransfer(byte sendByte)
return SPI.transfer(sendByte);
// this is irq handler for AS3935 interrupts, has to return void and take no arguments
// always make code in interrupt handlers fast and short
void AS3935Irq()
// there is no need for this flag anymore
// AS3935IrqTriggered = 1;
// I move all the code for dysplaiying events inside the interrupt routine
// again there is no need for this flag
// reset the flag
// AS3935IrqTriggered = 0;
// first step is to find out what caused interrupt
// as soon as we read interrupt cause register, irq pin goes low
int irqSource = AS3935.interruptSource();
// returned value is bitmap field, bit 0 - noise level too high, bit 2 - disturber detected, and finally bit 3 - lightning!
if (irqSource & 0b0001)
Serial.println("Noise level too high, try adjusting noise floor");
if (irqSource & 0b0100)
Serial.println("Disturber detected");
if (irqSource & 0b1000)
// need to find how far that lightning stroke, function returns approximate distance in kilometers,
// where value 1 represents storm in detector's near victinity, and 63 - very distant, out of range stroke
// everything in between is just distance in kilometers
int strokeDistance = AS3935.lightningDistanceKm();
if (strokeDistance == 1)
Serial.println("Storm overhead, watch out!");
if (strokeDistance == 63)
Serial.println("Out of range lightning detected.");
if (strokeDistance < 63 && strokeDistance > 1)
Serial.print("Lightning detected ");
Serial.println(" kilometers away.");
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment