Helium solar hotspot (Data-Only) 2021 update

In a previous blog post about 18 month ago, I designed my first Low Cost LoRaWAN Solar Gateway. This year, I did some updates to create a new version to support Helium Data-Only Hotspot (basically it works for any LoRaWAN networks like TheThingsNetwork).

In this version, I’m using a RAK wisegate Lite gateway, it is a bit more power consuming than the TTIG but can work on any LoRaWAN network. I’ve also changed the outdoor enclosure to get a larger and single battery.

You will also see that I’ve been updated the monitoring dashboard to get something better and free of charge. Two of them are in production. One is already deployed as an upgrade of the 1st one and the second one is in the testing phase. The First version has been on the field for more than a year. It has been offline about 10 days during that year, due to the weather conditions. This is a service level of 98,29% from its start until now. With the larger battery I’m expecting to resolve some of the small service interruption I’ve issued during last winter.

Bill of material

The overall price is about 700€ to 800€, you can optimize some of the components like the fixing parts of the main plastic box. Local store could be really lower cost for the pieces with high volume or weight.

Step 1 – preparing the outdoor enclosure

At the beginning we have to install the mat fixing element in the outdoor enclosure to fix it to the mat. We will try to center the fixing piece in the middle of the box.

Add the mat fixing part on the rear of the enclosure

Now we need to screw these two pieces and to avoid water intrusion, I’m adding to Silicon seal around:

Now we can screw the pieces and start processing the inner side of the box.

I’m placing some screws to attach the different components. The RAK gateway has 2 holes on the back so it is really easy to fix it with two screws. The MPTT harvester have 4 holes on the corner for screws. 2 of them will be enough.

The battery is fixed with 2 Colson/Serflex passing behind the metallic plate. To avoid vertical movement during transport I also use a 3M Dual Lock piece to fix the battery.

On the bottom of the enclosure, there is two larger hole with the cable pass. The one on the left will receive the Solar panel cable and the one on the right receives the radio cable to the antenna.

Once all of this has been made, it is now possible to screw the metallic plate to the plastic enclosure. Then we can start installing the main pieces into the box.

Step 2 – installing the monitoring tool

Monitor your Solar gateway is a key aspects to make sure it is working and quickly understand the reason why it’s broken when is it. Lake of sun or something else. In a case you can come with a fresh new battery or just wait, in the other, you need a larger investigation. Most of the time it’s the WiFi going down…

For monitoring the gateway, I’ve developed an open-source project based on an Arduino LoRa radio Node module I’m powering with a 4R25 battery. Than way, even when the main battery is off, the monitoring system continue to work (if you have a little redundancy in term of Helium network around).

You can read this previous blog post with all the details on the LoRaWAN Solar gateway monitoring project.

There are some little changes on this version:

  • The RAK gateway voltage is 12V so the voltage divider circuit I’m using is now 100K / 1M to have a division by 10.
  • As TheThings.io was too much expensive for a such use-case, I’ve been migrated the dashboard to Tago.io you can easily integrate with Helium console.

The decoding function inside the helium console is:

function Decoder(bytes, port) { 
  // Signed values
  var batC = 256*bytes[6]+bytes[7];
  if ( batC >= 32768 ) {
    batC = batC - 65536;
  }

  var boardTemp = (256*bytes[2]+bytes[3]);
  if ( boardTemp >= 32768 ) {
    boardTemp = boardTemp - 65536;
  }
  
  // specific board calibration
  boardTemp += -28;
  
  
  var batPower = (256*bytes[21]+bytes[22]);
  if ( batPower >= 32768 ) {
    batPower = batPower - 65536;
  }

  if ( batC > 0 ) {
    if ( batPower < 0 ) batPower = -batPower;
  } else {
    if ( batPower > 0 ) batPower = -batPower;
  }

  var batVoltage = (256*bytes[10]+bytes[11])/100.0;
   
  //if ( batPower > 10000 || batPower < -10000 || ( batPower > 0 && batC < 0 ) || ( batPower < 0 && batC > 0 ) ) {
  //  batPower = ((batC/100.0)*(batVoltage)*100.0);
  //}
  
  var decoded = {
    boardTemperature:boardTemp/10.0,
    batteryCurrent:batC/100.0,
    batteryVoltage:batVoltage,
    boardVoltage:(256*bytes[14]+bytes[15])/100.0,
    externalPowerState:bytes[18],
    batteryPower:batPower/100.0
  };

  return decoded; 
}

You may have to adjust the board temperature as each of the board will report it with a certain difference.

The Tago.io integration is automatically made by helium console. You will find different help on Internet about this. Then you can design you monitoring dashboard. Here is my dashboard:

Hotspot solar monitoring dashboard

Basically we have the charging/consuming graph on top, the battery level above, the temperature then the gateway powering state. When all the graph are blank it’s more about a communication issue, when only the lower powering state is blank, it’s a power issue.

Then you can setup alarms to get noticed in case of problems.

Once the software has been setup, it’s time to cable all of this:

Cabling the Solar Monitoring

The solar monitoring device is installed on the side of the box. 2 wires comes from the harvester 12v power out to monitor the state.

The harvester battery power in/out pass through the current sensor. Only the VCC is connected to that sensor, grounds comes from the harvester power out previously connected.

The monitor is connected with a 4R25 battery upper to it.

The LoRa radio node antenna is simply attached to the side of the box to make sure it will not moving around. The battery and the LoRa Radio node are attached to the box with 3M dual lock so they can be removed / reinstalled easily and they are well attached to the box.

Step 3 – Join the Helium network

Now, the gateway is powered ON and you can configure it to join the helium network. This is a data-only gateway. There are two different ways to make it joining:

These two solutions have been detailed in the blog post you can access following the links. On my case, I prefer the second one, it has less data transfer and less processing on the gateway, so it saves energy on the solar side.

Step 4 – attach the solar panel

It’s now time to assemble the last components, radio antenna and solar panel.

Once the enclosure has been attached to the mat and installed in the parasol stand you can pass the antenna cable and fix the antenna to the mat.

Now comes the solar panel

Attach the solar panel on the mat

Step 5 – finalization and test

Once everything is connected we can go to the final phase: make sure everything is connected and test it on an accessible place before installing it far away from you. 1 week of test to make sure the solar energy is correctly converted and the monitoring is stable is a good way to do.

Test installation before final deployment

Step 6 – On site install

The last step is to install the hotspot at its final place and correctly fix it to make sure it will support the string weathers. I’ll complete this blog post later once it will be installed. At the current time, the hotspot is in the test phase.

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