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“Data: My positronic brain has several layers of shielding to protect me from power surges. It would be possible for you to remove my cranial unit and take it with you.
Riker: Let me get this straight--you want me to take off your head?
Data: Yes sir”
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(2020-07-19 update: see also this blog post)
Now that all my new parts have arrived, the mantra with this next iteration is isolation. The first system came to a dramatic end at the very beginning of the monsoon season. Repeated lightning strikes in the space of just a few minutes damaged every single part of the last AS3935 lightning detector. The surge nearly always ran along the phone line running into my ADSL modem.
First we isolate the electronics in the direct line of fire: the relay module which disconnects the ADSL line from the modem. One encouraging result is my ADSL modem survived unscathed, which is the main aim of the AS3935. The lightning surge arrived at relay COM pin and flashed over to the 5Vdc line.
And if that should come up short, we separate the relay board from the AS3935 NodeMCU ESP-12E system. Henceforth they communicate over WiFi via an MQTT server.
And where it used to share the same 5V supply as the relay board, we will now run from its own; where previously it shared the AS3935's. This still means they still share the same mains 230Vac line. And since the lightning strikes coming along the ADSL line seeks out the AC mains Live or Neutral lines, we isolate that as well: the relay 5V supply shall be derived from a 12V lead-acid battery.
The battery needs to be float-charged from a mains charger, and as an extra precaution the charger will be disconnected from the mains using a separate relay module, again cued from the MQTT server. The server will need to be run from UPS as well.
The AS3935 system now only publishes to the MQTT server. It is powered directly from the mains; it normally detects the storm well beforehand, and if the stroke should take out the AC mains, it does not matter for its job is done. On restoration of power it gets the last state again from the MQTT server and resumes operation.
And for debugging instead of risking a laptop running Arduino IDE, debug messages are published to the same MQTT server. More details on setting up MQTT Server in Slackware here.
The MQTT server, ADSL modem as well as the Huawei 3G Failover router all run from a UPS so on detecting an imminent a lightning strike, the ADSL line is disconnected, and IoT remote services will get maybe 2 minutes interruption while the Huawei router switches to 3G.
As usual, the source code is in my github repository. The esp8266 code will look for an MQTT server at mqttserver.local on mDNS. Once located, they will subscribe to the topic lightning/commands and publish on lightning/messages.
An unexpected advantage is the AS3935 sensor can now be put in an electrically quieter part of the house. It seemed happiest at the back porch window, equidistant from the computers in the study and the power inverter of the refrigerator. This allowed me to increase the sensitivity setting.
For now it is set a little over-sensitive. A storm vertically overhead but too high up to trigger a strike to ground will still set it off. As does the little 50-cc 2-stroke engine from my brush-cutter. The occasional false ADSL disconnects did not bother us too much: the Huawei 3G failover system cuts over within 2 minutes, and even the IoT nodejs server does not drop its ngrok connection.
The stage is set. It is now the inter-monsoon, and thunderstorms are beginning to come overhead, this time from the south-west. And with the Covid-19 lockdown we will be at home, for the next bout of fireworks. And all I need now is the Big Strike.
After more than 20 years, I feel a little for Captain Ahab, as played by the same excellent Patrick Stewart:
Happy Trails.
P.S.: A promising new relay PCB from LC Tech has slots cut around the COM pins.
In the last setup, the lightning struck relay COM pin, and flashed over to the 5V relay coil power line. Now the relay coil drives are optically isolated, which means the 3.3V power for the ESP8266 is better shielded from the relay contact pins.
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| Next Generation System is all about MQTT |
First we isolate the electronics in the direct line of fire: the relay module which disconnects the ADSL line from the modem. One encouraging result is my ADSL modem survived unscathed, which is the main aim of the AS3935. The lightning surge arrived at relay COM pin and flashed over to the 5Vdc line.
 |
| ADSL Switch. Note the TTL serial lines running to the charger relay board. Hopefully the electricians' tape wrapped over the PCB traces and the relay terminals will help resist flashovers |
And if that should come up short, we separate the relay board from the AS3935 NodeMCU ESP-12E system. Henceforth they communicate over WiFi via an MQTT server.
And where it used to share the same 5V supply as the relay board, we will now run from its own; where previously it shared the AS3935's. This still means they still share the same mains 230Vac line. And since the lightning strikes coming along the ADSL line seeks out the AC mains Live or Neutral lines, we isolate that as well: the relay 5V supply shall be derived from a 12V lead-acid battery.
 |
From left: N40 lead-acid battery, battery charger. The white mains power cord of the charger is switched by another 2-channel relay module. Note the original charger display has been replaced by a 13.8V CV-CC DC boost-buck module |
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| AS3935 with NodeMCU ESP-12E ESP8266 board. Note the 5V power cable is filtered by a few loops round a ferrite doughnut |
The battery needs to be float-charged from a mains charger, and as an extra precaution the charger will be disconnected from the mains using a separate relay module, again cued from the MQTT server. The server will need to be run from UPS as well.
 |
| Charger mains supply cutoff relay. Note the TTL serial link from the ADSL relay module. |
The AS3935 system now only publishes to the MQTT server. It is powered directly from the mains; it normally detects the storm well beforehand, and if the stroke should take out the AC mains, it does not matter for its job is done. On restoration of power it gets the last state again from the MQTT server and resumes operation.
And for debugging instead of risking a laptop running Arduino IDE, debug messages are published to the same MQTT server. More details on setting up MQTT Server in Slackware here.
The MQTT server, ADSL modem as well as the Huawei 3G Failover router all run from a UPS so on detecting an imminent a lightning strike, the ADSL line is disconnected, and IoT remote services will get maybe 2 minutes interruption while the Huawei router switches to 3G.
As usual, the source code is in my github repository. The esp8266 code will look for an MQTT server at mqttserver.local on mDNS. Once located, they will subscribe to the topic lightning/commands and publish on lightning/messages.
An unexpected advantage is the AS3935 sensor can now be put in an electrically quieter part of the house. It seemed happiest at the back porch window, equidistant from the computers in the study and the power inverter of the refrigerator. This allowed me to increase the sensitivity setting.
For now it is set a little over-sensitive. A storm vertically overhead but too high up to trigger a strike to ground will still set it off. As does the little 50-cc 2-stroke engine from my brush-cutter. The occasional false ADSL disconnects did not bother us too much: the Huawei 3G failover system cuts over within 2 minutes, and even the IoT nodejs server does not drop its ngrok connection.
 |
| False alarm: a nearby internal combustion engine will trigger a stream of false alarms |
The stage is set. It is now the inter-monsoon, and thunderstorms are beginning to come overhead, this time from the south-west. And with the Covid-19 lockdown we will be at home, for the next bout of fireworks. And all I need now is the Big Strike.
After more than 20 years, I feel a little for Captain Ahab, as played by the same excellent Patrick Stewart:
 | ||
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Happy Trails.
P.S.: A promising new relay PCB from LC Tech has slots cut around the COM pins.
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| LC Tech 4-Channel Relay Module |
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| Note the slots cut around the relays' COM pin |
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