Lightning Detector AS3935: adding Serial Relay Module and MQTT Server Part 2 of 3

In Part 1, we interfaced the AS3935 lightning detector to an ESP-12E using SPI. In Part 2 here, we add an ESP-01 2-channel WiFi relay board and also set up an MQTT server.

But first, some test results. After running the system in Part 1 for a few weeks we know that:
1. There are many false (ie 'disturber') alarms
2. Some lightning strikes are incorrectly classed as 'disturber'
3. The little antenna is directional, so be careful positioning it
4. The AS3935 and relay module are best on separate 5V wires, otherwise there may be too many false alarms
5. The settings that worked for me are: Noise Floor: 3, Spike Rejection: 0, and Watchdog Threshold:2
6. There is good correlation between actual lightning strikes and the AS3935 readings
7. I have good results disconnecting the relays when the lightning is less than 5km (ie 'storm overhead') and reconnecting it 30 minutes after  lightning strikes are further than 8km away.

2-channel wifi relay module

ESP-01 2 Channel WiFi Relay Module

I got mine from lazada.com for RM27 (about USD4) each. Unlike the other ESP8266 relay boards this one has a separate CPU to activate the relays and instead of using precious GPIO pins you can do it with the serial port UART0.

makerrelay has a good writeup on a very similar module, complete with schematics and identical relay switching commands. Even better, libretto (Sergiy Zaschipas) shows you how to reprogram the relay CPU.

I can not only replace the ESP-01 with a NodeMCU ESP-12E, but I can now add relay 'channels' by simply adding more relay boards. I do not even have to use extra GPIO pins - the same TTL serial port UART0 can drive all the relay boards.

Another convenience is the relay outputs need not be reset especially since the ESP8266 is sometimes best reset if it is unable to reconnect to WiFi. If the relay CPU is reprogrammed, the ESP8266 may even read back the relay states. Since the AS3935 drops the phone line when a storm is overhead it can actually cause WiFi disconnects.

Based on some of the board markings, it is possible the original design is by LC Tech. LC Tech also provides documentation.

NodeMCU ESP-12E Pinout

You connect GP101 (also TXD0 or TX) to the pin (ESP-12E bottom right) marked 'TX' on the relay board. Connect up the adjacent GND pin to the correcponding relay module pin and you are good to go.

Relay module, solder side

Note that if you want to supply power to the relay board you need 5V which is on the other column of pins (VIN) of the ESP-12E, and not the very tempting 3.3V pin.

The relay commands are:

//Hex command to send to serial for close relay
byte relON[]  = {0xA0, 0x01, 0x01, 0xA2};
//Hex command to send to serial for open relay
byte relOFF[] = {0xA0, 0x01, 0x00, 0xA1};
//Hex command to send to serial for close relay
byte rel2ON[]  = {0xA0, 0x02, 0x01, 0xA3};
//Hex command to send to serial for open relay
byte rel2OFF[] = {0xA0, 0x02, 0x00, 0xA2};

To turn on relay 1:

Serial.write (relON, sizeof(relON));

It is that simple. My setup now looks like this:

AS3935 SPI and Relay serial port cables consolidated to one 2-headed monster. Note the 5V VIN cable on the far right. System power is via the USB cable (silver)

Top left to right: ESP-12E (partially hidden), relay module and AS3935

MQTT Server

Now that I have a way of disconnecting the ADSL modem, a convenient way to monitor the AS3935 results would be nice. Initially I simply printed the results using Serial.print() and got the output via the Arduino IDE Serial Monitor.

This worked when I am at my work station but pretty soon I was printing out to my Adafruit MQTT feed. This worked much better until a lightning storm came close enough for the relay module to disconnect the ADSL modem at which point the Adafruit connection got interrupted.

Now my WiFi does have a 3G failover, but it takes precious seconds for the Adafruit feed to re-establish itself and vital AS3935 messages are often lost. So one of the things to try would seem to be a local MQTT server, which could capture and retain my MQTT messages and if necessary upload them to my Adafruit feed for when I am offsite.

It sounds like a lot of work, until along came Mosquitto. Since my main station is still Slackware 14.2, I got my SlackBuild here:

As usual douwnload the SlackBuild tarball and unzip it:

$tar -xvpzf mosquitto.tar.gz
mosquitto/
mosquitto/slack-desc
mosquitto/README
mosquitto/mosquitto.info
mosquitto/doinst.sh
mosquitto/mosquitto.SlackBuild
usr/man/man8/mosquitto.8.gz
usr/sbin/
usr/sbin/mosquitto
usr/share/

Then download the mosquitto source code (from the SlackBuild link not the Eclipse one) and copy it into the mosquitto slackbuild directory. Then all you need is

$./mosquitto.SlackBuild

And then a Slackware install:

$upgradepkg --install-new /tmp/mosquitto-1.6.7-x86_64-1_SBo.tgz

Next you need to set up a mosquitto user:
$vi /etc/mosquitto/mosquitto.conf

And add the line:
user mosquittouser

If necessary create the new user:
$adduser mosquittouser

You start the server thus:
$mosquitto -c /etc/mosquitto/mosquitto.conf
1572678454: mosquitto version 1.6.7 starting
1572678454: Config loaded from /etc/mosquitto/mosquitto.conf.
1572678454: Opening ipv4 listen socket on port 1883.
1572678454: Opening ipv6 listen socket on port 1883.

And to check use the included client subscriber:

$mosquitto_sub -t 'test/topic' -v

The publish:

$mosquitto_pub -t 'test/topic' -m 'hello world of mosquitto'

And that was all you need. I suspect it is even easier in Debian/Ubuntu. The next thing I need would be an MQTT client for the ESP-12E, but that is another story.

So till then, Happy Trails.