Lightning! The Lightning Detector for Raspberry Pi Weather Station

In this Instructable you will learn:

  1. How to a connect a Lightning Detector to a Solar Powered Weather Station
  2. How to design and position the lightning detector for best perfomance
  3. How to gather data to see the Lightning story as it happens
  4. How to wire up a the lightning detector to an I2C Mux and a Raspberry Pi
  5. Building 3D Printed Parts for the pylon to hold the Lightning Detector
  6. Examine the Python software for running the Lightning Detector on a Raspberry Pi

Recently, we published an Instructable detailing how to build a solar powered Raspberry Pi weather station, WeatherPi.

What is Weather Pi?

WeatherPi is a solar powered Raspberry Pi WiFi connected weather station designed for Makers by SwitchDoc Labs. This is a great system to build and tinker with. All of it is modifiable and all source code is included. The most important functions are:

  • Senses 20 different environmental values
  • Completely Solar Powered
  • Has a full database containing history of the environment (MySQL)
  • Monitors and reports lots of data on the solar powered system – great for education!
  • Self contained and monitored for brownouts and power issues
  • Can be modified remotely
  • Download your data to crunch it on your PC
  • Can be modified to do SMS (Text) messaging, Twitters, webpages and more
  • Has an iPad Based Control Panel
  • Easy to connect to Twitter, WeatherUnderground, etc

Enter the Lightning

This Instructable will show you how to add an Embedded Adventures MOD-1016 AS3935 Lightning Detector Breakout Board to the Solar Powered Raspberry Pi Weather Station.

Follow along on updates to the WeatherPi story on www.switchdoc.com.Lightning! The Lightning Detector for Raspberry Pi Weather Station

What is the AS3935 and How Does It Work?

The Austrian Microsystems AS3935 is a programmable Lightning Sensor IC that detects the presence and approach of potentially hazardous lightning activity in the vicinity and provides an estimation on the distance to the head of the storm. The embedded lightning algorithm checks the incoming signal pattern to reject the potential man-made disturbers and various noise sources.

The AS3935 can also provide information on the noise level and inform the Raspberry Pi of high noise conditions.

Step 1: Connect the Lightning Detector to WeatherPi

The complete Instructable for building WeatherPi, a solar powered Raspberry Pi based Weather Station, including the parts list and full wiring list is here.

Since we left our other MOD-1016 AS3935 breakout board on the WeatherPiArduino board for the time being, we decided to add an additional MOD-1016 AS3935.

Since the MOD-1016 has a fixed I2C address (0x03), we couldn’t connect it up to the same I2C bus as the WeatherPiArduino board is on. So, using the I2C Multiplexer board, we put the second MO-1016 on bus 2.

We are always running into conflicts with addressing on the I2C device. Since there are no standards, sometimes multiple devices will have the same address, such as 0x03, and you are just out of luck in running both of them on the same I2C bus without a lot of jimmy rigging.

4 Channel Multiplexed I2C Breakout Board

To get around this addressing problem (specifically the conflict between an INA3221 and the Inside Humidity Sensor as well as having two identical lightning sensors – see below) we added an I2C Bus Multiplexer to the design which allows us to have many more I2C devices on the bus, irregardless of addressing conflicts. Below is our current list of I2C devices in WeatherPi.

Module Address I2C Mux Bus #
BMP180 Barometric Pressure 0x77 Bus 0
Real Time Clock DS3231 0x68 Bus 0
ATC EEPROM 0x56 (or 0x57) Bus 0
ADS1015 Analog to Digital Converter 0x49 Bus 0
FRAM non-volatile storage 0x50 Bus 0
ADS1015 on SunAirPlus 0x48 Bus 1
INA3221 3 Channel Voltage/Current Monitor on SunAirPlus 0x40 Bus 1
Embedded Adventures Lightning Detector 0x03 Bus 0
Embedded Adventures Lightning Detector 0x03 Bus 2
AM2315 Outdoor Temp/Humidity 0x5C Bus 1
I2C 4 Channel I2C Bus Mux 0x73 On All Busses
HTU21D-F Humidity Sensor 0x40 Bus 0

Note that a number of devices have the same address. This is fixed by using the I2C Mux Breakout Board.

Wiring List

These are just the additions to the wiring list for the AS3935 Breakout Board connected to Bus2 of the I2C Mux and placed in the 3D Printed Pylon. The full wiring list for WeatherPi is in the Instructable.

I2C Mux Board (I2CM)
JP5 – I2C Bus2 External AS3935 Breakout Board (ASBB)
I2CM JP5/Pin 2: VD2 3.3V From Pi/Screw Connector 3.3V From Pi/Screw Connector
I2CM JP5/Pin 3: GND ASBB: GND GND for ASBB Board
I2CM JP5/Pin 4: SC2 ASBB: SCL SCL for ASBB Board
I2CM JP5/Pin 5: SD2 ASBB: SDA SDA for ASBB Board
External AS3935 Breakout Board (ASBB)
External AS3935 Breakout Board (ASBB) JP5 – I2C Bus2
ASBB: VCC 3.3V From Pi/Screw Connector 3.3V From Pi/Screw Connector
ASBB: GND I2CM JP5/Pin 3: GND GND for ASBB Board
ASBB: SCL I2CM JP5/Pin 4: SC2 SCL for ASBB Board
ASBB: SDA I2CM JP5/Pin 5: SD2 SDA for ASBB Board
ASBB: IRQ PiA+ GPIO/Pin 15: GPIO 22 IRQ Line to Raspberry Pi

Here is what the I2C bus looks like on the Raspberry Pi. This is the output from the example code with the I2C 4 Channel Mux (hence there are 4 independent busses shown for the I2C bus).
Note that WeatherPi uses Bus 0, Bus 1 and Bus 2.

Bus 2 is only used for connecting to the external MOD-1016 AS9535 Lightning detector. Running the test software for the I2C Mux Breakout Board gives the following results:

Test SDL_Pi_TCA9545 Version 1.0 - SwitchDoc Labs

Sample uses 0x73
Program Started at:2015-05-19 02:45:59

-----------BUS 0-------------------
addr = 0x73 returndata = 0x81 
tca9545 control register B3-B0 = 0x1
ignore Interrupts if INT3' - INT0' not connected
tca9545 control register Interrupts = 0x8
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          03 -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: 40 -- -- -- -- -- -- -- -- 49 -- -- -- -- -- -- 
50: 50 -- -- -- -- -- 56 -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- 73 -- -- -- 77                         

-----------------------------------

-----------BUS 1-------------------
addr = 0x73 returndata = 0xa2 
tca9545 control register B3-B0 = 0x2
ignore Interrupts if INT3' - INT0' not connected
tca9545 control register Interrupts = 0xa
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: 40 -- -- -- -- -- -- -- 48 -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- 73 -- -- -- --                         

-----------------------------------

-----------BUS 2-------------------
addr = 0x73 returndata = 0x84 
tca9545 control register B3-B0 = 0x4
ignore Interrupts if INT3' - INT0' not connected
tca9545 control register Interrupts = 0x8
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          03 -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- 73 -- -- -- --                         

-----------------------------------

Step 2: Testing the Lightning Unit

Not surprisingly, this lightning detection device is very sensitive to RFI (Radio Frequency Interference) sources. If you have your device next to a monitor, it will not work well. If you have it next to a cell phone, it will not work well. As you will see below, we had to mount the detector well away from the Raspberry Pi and Solar Power Controller to get it to work well.

When we found the AS3935 device, we were pretty excited about using it in a design. One of the issues we quickly found ourselves facing was how to test the AS3935 in our own design. As noted in a previous step, we could cause noise to happen by placing close to monitors and cell phones (which actually tests a lot of the hardware and software, but nothing really about sensitivity in a measured, calibrated way), but we wanted something more accurate to test it with. We could cause interrupts (mostly of the noise floor type), but few lightning bolts.

We ended up buying the AS3935 Touch Sensor Development Tools Franklin Lightning Sensor IC Development Kit from mouser.com. It set us back $230, which was more than we wanted to pay, but we quickly used it to diagnose a number of the problems in the design and the device placement.

As we were finishing this Instructable, an actual thunderstorm came by SwitchDoc Labs. Unfortunately, We had the AS3935 all taken apart in pieces, so we grabbed the development kit and turned it on and were quickly rewarded with a number of lightning bolt detections.

Later on in the weekend, a real thunderstorm rolled through about 6km away and produced this data, shown on RasPiConnect. The WLAN Down messages are from an ongoing problem with WiFi disconnects. We reset the WiFi dongle if there is a disconnect and log the event.

These detections were after we moved the lightning detector out into the pylon (actually, we just added another one rather than unsolder the one on the WeatherPiArduino – we will do that later next week).

Step 3: 3D Print your Lightning Pylon

Problem Mounting the AS3935 Inside the Box

We installed the MOD-1016 containing the AS3935 on the header provided on the WeatherPiArduino board. You can see it installed in the center of the picture below.

The AS3835 Breakout Board Installed on WeatherPiArduino

This turned out not to be a good location. Too much noise from all the other components surrounding it. We were getting interrupts telling us to adjust the noise floor and then you had to be right on top of it with the lightning simulator to get any response at all. We needed to move it away from the other electronics. In hindsight, we should have known that this would happen. The solution? Move it away from the box in a pylon. We thought of moving the WeatherPiArduino into a pylon, but we decided to just put an AS3835 in the pylon. See the 3D Print files above. Below is what the three parts look like on the screen in OpenSCAD and then it is followed by a picture of the pylon printed and installed on the WeatherPi Box. Here are the OpenSCAD files for the pylon.

The 3D Printed Parts of the Lightning Pylon

Step 4: The Software for the Lightning Detector

After quite the search and playing with a number of packages, we found a good package by Phil Fenstermacher. With a little fooling around and setting up interrupts, we got the software to work.

The full software for WeatherPi, which includes the AS3935 software is available on github.com.

Here is the setup software:

################

# ad3935 Set up Lightning Detector

# turn I2CBus 2 on
tca9545.write_control_register(TCA9545_CONFIG_BUS2)
time.sleep(0.003)
#tca9545.write_control_register(TCA9545_CONFIG_BUS0)
#time.sleep(0.003)

as3935 = RPi_AS3935(address=0x03, bus=1)

as3935.set_indoors(False)
as3935.set_noise_floor(0)
#as3935.calibrate(tun_cap=0x0F)
as3935.calibrate(tun_cap=0x05)

as3935LastInterrupt = 0
as3935LightningCount = 0
as3935LastDistance = 0
as3935LastStatus = ""

as3935Interrupt = False
# turn I2CBus 0 on
tca9545.write_control_register(TCA9545_CONFIG_BUS0)
time.sleep(0.003)

Lightning! The Lightning Detector for Raspberry Pi Weather Station schematicNext the processing software for the Interrupts.

def process_as3935_interrupt():

    global as3935Interrupt
    global as3935, as3935LastInterrupt, as3935LastDistance, as3935LastStatus

    as3935Interrupt = False

    print "processing Interrupt from as3935"
    # turn I2CBus 0 on
    #tca9545.write_control_register(TCA9545_CONFIG_BUS0)
    # turn I2CBus 2 on
    tca9545.write_control_register(TCA9545_CONFIG_BUS2)
    time.sleep(0.003)
    reason = as3935.get_interrupt()

    as3935LastInterrupt = reason

    if reason == 0x00:
        as3935LastStatus = "Spurious Interrupt"
    elif reason == 0x01:
        as3935LastStatus = "Noise Floor too low. Adjusting"
        as3935.raise_noise_floor()
    elif reason == 0x04:
        as3935LastStatus = "Disturber detected - masking"
        as3935.set_mask_disturber(True)
    elif reason == 0x08:
        now = datetime.now().strftime('%H:%M:%S - %Y/%m/%d')
        distance = as3935.get_distance()
        as3935LastDistance = distance
        as3935LastStatus = "Lightning Detected "  + str(distance) + "km away. (%s)" % now
        pclogging.log(pclogging.INFO, __name__, "Lightning Detected "  + str(distance) + "km away. (%s)" % now)

    print "Last Interrupt = 0x%x:  %s" % (as3935LastInterrupt, as3935LastStatus)
    tca9545.write_control_register(TCA9545_CONFIG_BUS0)

    time.sleep(0.003)

The Interrupt Handler. Short and Sweet, as interrupt handlers should be.

def handle_as3935_interrupt(channel):
    global as3935Interrupt

    print "as3935 Interrupt"

    as3935Interrupt = True

Setting up the Raspberry Pi GPIOs to receive interrupts.

#as3935pin = 18
as3935pin = 22

GPIO.setup(as3935pin, GPIO.IN)
#GPIO.setup(as3935pin, GPIO.IN,pull_up_down=GPIO.PUD_UP)
GPIO.add_event_detect(as3935pin, GPIO.RISING, callback=handle_as3935_interrupt)

And the reporting software for reading the Interrupts.

        # process Interrupts from Lightning

        if (as3935Interrupt == True):

                try:
                        process_as3935_interrupt()


                except:
                        print "exception - as3935 I2C did not work"

 

For more detail: Lightning! The Lightning Detector for Raspberry Pi Weather Station

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