Help me with designing a node
Help me with designing a node
I want to put a node up on my house to act as a repeater or station, but I don't know how to spec it from the PCB available as-is on Aliexpress and other venues.
So - what would you do?
- Which board
- Which antenna
- Which power source (solar + battery?)
It needs to function on an unheated loft in Denmark year-round...
Surely, some of you have done this before, so please halp :)
The first thing for the EU area would be to check which frequency is more popular in your country. There are 2 options. 868Mhz, and 433Mhz. The good quality lora modeules are tuned for one or the other. There's no way to switch. 868 tends to be the most popular choice. I personally never understood that decision, but my knowledge of physics is limited by what the youtube science communicators can package up for easy consumption.
If you want solar power and don't mind the lack of wifi, I'd go with an nrf based solution like RAK4631 due to its low power consumption. Ideally in a form of a kit with base board included. If the wifi is needed, go with ESP32 and a larger solar panel.
I'm testing this ready made node at the moment. It looks a bit pricey, but if you count each component, it might even be cheaper than fully DIY solution. However, even though the nrf based chips have pretty low power consumption, I'm not sure it would survive the winter in denmark. The lack of dedicated power supply capable of low voltage cutoff might also be a problem if we expect the battery to run out regularly.
There are multiple possibilities when it comes to power storage. The LiFePo4 cells are pretty close to perfect, but can't charge in freezing temperatures. It's possible to build a heating system, but switching to LTO cells is way easier. If you want to experiment with different type of battery cells, there's a custom board using the RAK4631 module, compatible with both battery cell types, and capable of proper power management here. A Full kit including a 10W solar panel and 3D printed mounting accessories is also available.
In regards to solar panel and battery size, you can go wild with a tool like this. It can calculate the right values for your specific geographic location.
As for the antenna, the direct visibility goes 90% of the way. The antenna included with your kit should be sufficient for playing around. If you plan to set up a repeater for the larger area, you can go for something decent like Mikrotik Omni 868Mhz
If you want a visual example, look at this video describing the construction of now retired product - Atlavox S4. Similar parts can still be found on AliExpress. I've built one of those several months ago, and it's still going:
And finally, in case you don't find any online peers around you, try a different modem preset, or checkout Meshcore. Europe is slowly adopting it as a Meshtastic replacement for larger networks.
I can think of two reasons (well, actually three) why 868MHz is used more than 430MHz.
@deafboy @EvilCartyen
Antenna: smaller than 17cm for 868 sucks.
Dont use these if you dont need this small size like for fit a small node in yozr pocket never use this inefficient things in places where you can put a real antenna.
Dont know how tight the budget is, there are very cheap options if needed with good performance.
Solar for the european winter: a 5v solar panel with more than 500mA real current (like 30 or 35 "chinese watts"). Look for panels with sizes like 15x30 cm or bigger
Get a big battery for the winter weeks with no sun. 5Ah at least. Combine this with nrf52 based hardware.
So a 5Ah cell will be charged from a 0,5A solar panel with 0,1C charging current. This low currents are not critical in cold temperatures.
Bigger battery = lower charge current (current per battery capacity) 500mA for a 10Ah battery will be 0,05C current only. With this small charging currents normal li-ion cells are useable in the winter too.