Copy my homework! My minimalist Meshtastic solar node

Recently, a group member asked for some helpful reference node examples to share with the blog. This way, even those without a strong technical background can easily experience the joy of Meshtastic DIY. To address this need, I decided to share a solar node (Meshtastic build) that I built over a month ago.

The Meshtastic Solar Node is a standalone, solar-powered wireless device that provides connectivity to the Meshtastic network in locations without traditional electricity. Compared to other nodes that rely on batteries or external power sources, the Solar Node's key advantage is that it automatically recharges via solar power, ensuring long-term, unattended operation in outdoor environments.

Building a Meshtastic solar node allows you to provide a long-term stable expansion point for the network while reducing the trouble of frequent charging. Currently, users often place solar nodes on balconies, rooftops, and trees.

Material

When building a Meshtastic solar node, choosing the right components is key to ensuring system stability and long-term operation.

In order to simplify the description, this article puts the content of MPPT charging board in the sustainable optimization section in the latter half . HYPERLINK "https://meshcn.net/contact"  After reading the article, Ben Gao Aiwen strongly recommends purchasing an MPPT charging panel, which costs just a few bucks. He said, "These few bucks can instantly solve many problems, such as poor solar panel angles or insufficient power, saving people a lot of trouble. It's the best ten bucks he's ever spent."

solar panels

Solar panels are the energy source for the entire system, responsible for converting sunlight into electrical energy and providing a continuous power supply for the equipment.

We use a small monocrystalline solar panel:

· Dimensions: 165mm x 65mm

· The voltage is 6V.

· The current is 250mA.

· The power is 1.5 W. The power calculation formula is voltage multiplied by current.

After careful selection, I chose a size that would fit perfectly on the lid of the waterproof box.

The power is also sufficient. When choosing the solar panel, I calculated the required power based on the power consumption of the nRF52 node to ensure that the solar panel can meet the node's continuous operation requirements without an external power supply.

The advantage of equipping Meshtastic nodes with solar panels is that they can be automatically charged, which is especially suitable for unmanned application scenarios such as rooftops and suburbs.

Battery

Batteries are a key component of solar nodes. They store the electricity converted by solar panels, allowing the node to continue operating even when there's no sunlight. For Meshtastic solar nodes, choosing the right battery configuration is crucial for system stability and long-term operation.

We used 18650 lithium batteries in a parallel configuration, with a nominal voltage of 3.7V per cell.

Battery Science Class: The Difference Between Parallel and Series Connections

Parallel connection involves connecting the positive and negative terminals of multiple batteries together. This results in the battery voltage remaining constant, but the battery capacities (mAh) are added together, increasing the total charge. For example, if you have two 2000mAh, 3.7V batteries connected in parallel, the total capacity becomes 4000mAh, but the voltage remains at 3.7V. This allows the batteries to provide continuous power for a longer period of time.

A series connection connects the positive terminal of one battery to the negative terminal of the next. The total voltage of the series battery pack is the sum of the individual battery voltages, but the capacity remains the same. For example, two 2000mAh, 3.7V batteries connected in series have a voltage of 7.4V, but the total capacity remains at 2000mAh. While this method increases voltage, it also increases voltage. However, if the battery voltage is too high, it may exceed the operating range of some devices, causing them to malfunction.

The reason for choosing parallel connection instead of series is that the Heltec T114 node is designed to operate with a battery voltage of 3.7 V. If we used a series configuration, the battery voltage would be increased to 7.4 V or higher, which exceeds the voltage input range of the T114 and prevents the device from functioning properly.

In a parallel configuration, the positive and negative terminals of each battery are connected in parallel, while the total voltage remains unchanged at 3.7 V. However, connecting multiple batteries in parallel increases the total current output capability of the battery pack, enabling it to continuously power the node for a longer period of time.

In order to facilitate the installation and replacement of batteries, we choose to use a battery box to accommodate this set of parallel lithium batteries. The use of a battery box has several obvious advantages:

1. Easy installation: Compared to directly soldering batteries to the circuit board, the installation process of the battery box is much simpler. Users only need to place the batteries in the battery box and connect the corresponding terminals without the need for tedious soldering work. This makes the entire construction process more efficient and simple.

2. Another advantage of using a battery box is that it allows for easy replacement of batteries if they become defective or run out of power. Compared to soldering batteries, a battery box provides a more flexible and user-friendly replacement method, eliminating the need for re-soldering.

Waterproof distribution box

To protect the node's electronic components from the elements, we used a waterproof distribution box. This effectively blocks rain, moisture, and dust, ensuring the safety and stability of the components within. The box we selected measures 200 x 100 x 70mm, providing ample space to accommodate all components while also being robust enough to withstand the challenges of outdoor environments.

The protection level of this distribution box is IP65, which can ensure that the equipment can still work normally in rain or humid environments.

In addition to being waterproof, it can also effectively block the intrusion of dust and other external substances, increasing the durability of the device.

Meshtastic Module - Heltec T114

The Heltec T114 is the core of this node. It is a device that integrates a LoRa communication module, a power-saving nRF52 microcontroller (MCU), Bluetooth and various interfaces, and is designed for low-power wireless communication.

When choosing hardware, the nRF52 is generally preferred for building Meshtastic solar nodes, given the high power consumption of the ESP32. Currently, there are two main commercially available nRF52 Meshtastic development boards: RAK and Heltec's T114. The RAK is very popular in the international community, but it's relatively expensive, so I haven't personally tried it. The Heltec T114, on the other hand, is my preferred choice due to its affordability and stable performance. I'm using the Heltec T114 this time, and I already have three of these boards in my possession, with no significant issues. The T114 is also a popular choice for building solar nodes in the community. The MeshCN blog has shared extensive information about the T114, so please feel free to search and read .

If you're interested in DIY and cost-effectiveness, you can also check out the frequently mentioned fakeTec project in the community . This project, also based on the nRF52, offers excellent value for money, but requires advanced soldering skills to assemble. Since this article is geared towards beginners, I won't go into the details of fakeTec. Interested users can learn more about it in the community.

The Heltec T114 features built-in LiPo battery and solar panel connectors, making it incredibly convenient to connect directly to the battery and solar panel. This eliminates the need for additional soldering or third-party charging modules, making the entire setup process much simpler and reducing the potential for error. This makes it incredibly user-friendly for beginners.

antenna

The antenna is a key component for the Meshtastic Solar Node to communicate with other Meshtastic nodes.

I chose the Gizont High-Gain Soft Whip Antenna. I initially chose this antenna because I saw many users on Reddit giving it high praise, saying it offers a good balance of performance and price. Recently, some community members tested the antenna using professional equipment, and the results confirmed its excellent performance in the 470-510 MHz band.

When buying an antenna, please note that you need to buy one in the 470-510 MHz frequency range, as this will be suitable for Meshtastic's frequency band in China.

In addition, you will need to buy an IPEX 1st generation to SMA adapter. Note that the adapter specification should be external thread internal hole, not external thread internal pin.

The adapter is needed because the antenna connector on the Heltec T114 is an IPEX generation connector, while the Gizont antenna uses an SMA connector. In order to make the antenna compatible with the T114, you must purchase an IPEX to SMA adapter to connect the two.

Tools and Assembly

Before you begin assembling your Meshtastic solar node, be sure to gather all the necessary tools and materials. These tools and procedures are designed to help you easily install the node and optimize its performance. Below is a detailed assembly process, with detailed instructions and precautions for each step.

1. Preparation and installation of solar panels

First, to ensure 24/7 power, you need to solder the solar panel's output wires to the correct terminals. The standard practice is to use a red wire to the positive terminal (marked "+") and a black wire to the negative terminal (marked "-"). To ensure a secure connection, slightly heat the solder joint and use high-quality solder.

After soldering is complete, secure the solar panel to the cover of the waterproof distribution box. Drill two holes in the cover. The diameter of the holes should be slightly larger than the outer diameter of the cables (usually 3-5 mm) to facilitate the passage of the cables and ensure a tight seal. Once the cables are threaded through, solder the ends of the cables to the mating terminals on the Heltec T114 solar interface. Insert the cables into the T114's solar interface, ensuring correct polarity.

2. Installing the battery box and batteries

To provide a stable power source for the device, a parallel 18650 lithium battery pack was selected. Parallel rather than series connection was chosen because the Heltec T114's battery connector expects a 3.7V input voltage, which matches the output voltage of the parallel battery pack. Furthermore, using a battery box significantly simplifies the assembly process, eliminating the need for direct soldering to the batteries and reducing operational errors and safety risks. Furthermore, the battery box facilitates subsequent maintenance, such as battery replacement.

After fully charging the 18650 lithium batteries, place them into the battery holder according to the correct polarity. Ensure the positive terminals of all batteries face the red connector wire and the negative terminals align with the black connector wire. Once completed, connect the battery holder to the Heltec T114's battery connector. Ensure the connector is securely connected and cover the connector with electrical tape to prevent accidental removal.

3. Installing the SMA Adapter and Antenna

Next is the antenna installation. The Heltec T114 is equipped with an IPEX Gen 1 interface, while the high-gain Gizont antenna uses a standard SMA connector, so an IPEX to SMA adapter is required to connect them.

Drill a 6.1-6.2mm diameter hole above the waterproof distribution box to install the SMA adapter. Insert the adapter body from the inside of the box, ensuring the SMA connector's retaining nut and washer are located outside the box. Place the sealing ring inside the box to compress the connector and create an effective waterproof seal. Tighten the nut, preferably using a wrench to gently tighten it to ensure a secure fit. Then, screw the SMA antenna onto the outside of the adapter. Connect the IPEX connector inside the adapter to the T114.

4. Final system wiring and inspection

After installing the solar panels, battery box, and antenna, you need to connect all components to the Heltec T114 and check the wiring one by one. In particular, make sure:

· All terminals are connected with correct polarity.

· Check whether the SMA interface is tight to prevent it from loosening due to vibration or wind.

· Check whether the wires of the solar panel are firmly welded to prevent breakage due to pulling.

After completing the installation, close the cover of the waterproof distribution box and secure it with screws to ensure that each interface remains waterproof.

5. Start and test the node

Once all connections are complete and the antenna is connected, you can power on the device. You can connect to the device through the Meshtastic app or web interface to verify that the nodes are communicating properly and that the solar panels are charging the batteries. Once testing is complete, the device can be deployed in a real-world scenario.

Actual experience

After deploying this set of solar nodes in a real environment, I placed the device next to a south-facing window to ensure that it receives sufficient sunlight every day.

Although the angle of the solar panel is almost 0 degrees (because it is close to the window), the window faces south and the sunlight conditions are good, so the charging effect of the solar panel is still very stable.

I used a 1.5W, 6V 250mA solar panel, and despite the less-than-ideal angle, the overall power supply didn't drop significantly. After a day of use, I found that I was consuming about 1% of the battery each day, which means the system's energy consumption is relatively stable.

The battery pack utilizes 18650 lithium-ion cells, connected in parallel to ensure sufficient power to maintain normal operation. To avoid over-reliance on external power, the device is charged directly via the solar panel's built-in port, while the battery is connected via the T114's built-in battery port. Despite the direct connection between the solar panel and battery, the device remains stable in full sunlight. Overall, this system is well-suited for outdoor environments, particularly those without a power source, ensuring automatic charging and continuous operation.

I plan to continue optimizing the following parts

Add MPPT module to improve charging efficiency

Although the existing configuration can maintain stable operation, if the MPPT module is added, the charging efficiency will be greatly improved according to the calculation results of the previous solar MPPT efficiency article .

The MPPT (Maximum Power Point Tracking) module automatically adjusts the operating state of the solar panel based on the ambient light intensity, ensuring that the solar panel is always at the optimal power output point. This method not only improves charging efficiency in low-light conditions, but also prevents overcharging in strong sunlight.

Therefore, adding MPPT modules is an important step to improve the overall performance of the system, especially for solar equipment used outdoors for a long time.

Adjust the angle of the solar panel to improve charging effect

Currently, the solar panels are almost attached to the windows, with an angle close to 0 degrees. Although this can provide a certain charging effect, it is far from enough from the perspective of optimal solar energy utilization.

Based on my understanding of solar panel power output, the best placement angle should be around 20 degrees. This can better capture direct sunlight, especially in winter or when the light is weak.

I'll use the Solar Optimum Angle Calculator to optimize the angle of my solar panels based on my location's latitude to maximize power output. These simple adjustments will significantly improve the panels' energy collection efficiency and ensure the system continues to operate efficiently under varying lighting conditions.

Increase moisture-proof and breathable functions

Although current waterproof distribution boxes have effectively protected the electronic components of the equipment from rain and moisture, some moisture may accumulate inside the equipment over time, especially in humid environments.

To prevent this, I plan to add vents or exhaust holes to the distribution box. These features ensure that moisture inside the box can escape smoothly while maintaining the device's IP67 waterproof rating. Adding ventilation not only effectively prevents moisture damage to electronic components but also extends the life of the device.

In outdoor environments, moisture-proof and breathable measures are particularly important, especially in areas with unpredictable climate changes.

Increase battery capacity to ensure long-term stable operation

The current battery configuration is two 18650 batteries connected in parallel, which is sufficient to support the operation of the system. However, if we consider the situation of long periods of rainy weather or insufficient charging of solar panels, increasing the battery capacity will make the system more stable and reliable.

The battery box itself supports up to four batteries, and the entire waterproof distribution box has enough space to accommodate more batteries. Therefore, you can consider increasing the number of batteries, such as expanding to four or more batteries. This will ensure that the system can continue to operate stably even in the absence of sunlight for a long time.

While increasing the battery capacity, it can also effectively improve the system's backup power, providing more adequate protection for the continuous operation of the equipment.

Summarize

Building a Meshtastic solar node was both a challenging and rewarding project. By combining solar panels, batteries, and wireless communication technology, we were able to create a self-sufficient, long-lasting wireless communication node. This node not only provides constant connectivity for the Meshtastic network, but also plays a vital role in remote areas or outdoor environments without traditional power supply.

In this guide, we explain in detail how to select and assemble key components, including solar panels, batteries, antennas, and radio modules, and provide complete assembly steps. By following these steps, you can achieve solar power for your device and ensure continuous and stable operation in various environments.

Author: Hays Chan | Community blogger

Translator:Joe Tan | KEEPTEEN | meshtastic node repeater

Website: https//www.keepteen.com

Article link:https://www.keepteen.com/blog-Solar-Lora-12710/Copy-my-homework-My-minimalist-Meshtastic-solar-node-11941196.html