Solar power lora node, no battery

Hello all.
I want to share my own made loara node. My idea is to try to make a cheap node that will measure temperature humidity and soilmoisture (capacitive soil moisture sensor) for appel farmers in my area.

The specs are as follow:
MCU: Is a atmega 644p running at 3.3v 8mhz internal crystal.
Power: 5.4v 7.5F super capacitor
Charging: 6V 35mA solar panel.
Communication: rfm95w
I/O: 7 analog 8 digital
Sensor power:A extra LDO which can be turned on and off when power needed for sensors which draw more current
than the MCU digital i/o.
Housing: standard PVC pipe parts
Design had a RTC but did not see a need for it.

The current node has a dth22 to measure inside temperature. An digital i/o is used as power supply
for the dth22.
I want to know how hot it is getting inside of the housing.
A Soilwatch10 as capacitive soil moisture sensor. This is fed trough the second ldo because it draws 25 mA.

Did not measure how much power my setup uses but with a full charge of 5.4V and
no solar panel attached it can run 2 days while measuring battery voltage,
temperature, humidity and soil moisture every 30 minutes. After 2 days voltage dropped around 3.5V. So it can run 2.5 days (till 3.3V)without charging.

When it is using the solar panel it will drop from 5.4 volt till 4.8 in the morning. In the morning behind my house in the shade the capacitor get charged in around 2 hours.
For this setup the solar panel is too big but it was the smallest I could find.

For the next version I will make the pcb a bit smaller and fix some mistakes.
Total cost of lora node in the picture without the sensors (dth22 and soilwatch) 32euro.

Now I’m busy with the web-application and I still need to find a farmer where I can test 10 nodes out.

Keep on hacking



you can increase the supercapacity by using more then one C, but use a balance board.
for example : (not searched for the cheapest!)

Yes I know those boards. But the node runs good with 5.4F supercapacitor. Even on a cloudy day it will be fully charged.
And can run 2.5 days in total darkness.

so you’re charging the cap directly from the solar panel, just using the diode to prevent it from discharging through it - right?

curious how this porject develops, keep us updated! :open_hands:

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You could use this beast with 6x500F supercapacitors :smiley:

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Interesting project @gpenzo Please keep us updated.

I’am just doing some research googling for cheap solar+battery powered designs for loraclients (notgateways) and it seems like there are only expensive solutions out there. I stumbled over solar powered garden lights… maybe those are sufficient for setting up an autonomous lora temp/humidity lora client. What do you think? They are really cheap e.g. at ebay or amazon:

garden light with very small solar panels at 6 items for 16 Euros … ebay:

garden light with larger solar panels 4 items 30 Euros:

This is not an affiliate link or somethiink like taht - I’am just courious if this could be used… anyway, maybe out of scope of your post : )

why not ? The WORKBENCH part 3 :wink:

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Thanks for the link!

If your node does not send data packets too often and the sensors do not consume too much energy, your setup should work.

Below a photo of one of my nodes (Temp/Hum) with a small 8x6cm solar panel and a 18650 from an old Dyson vacuum cleaner battery pack.


The node has been active for 6 months now “outside in the cold distance”



it’s a bit of a mess here on my terras, don’t have a running outdoorgateway @ the moment.
but next week all is done and I’m planning to place a few solar nodes too.

one is build from the mentioned outdoor light

with this one build inside (if it fits :sweat_smile:)

  • I realize now that I have a battery inside… oops I’m not on topic :disappointed:
    I have to change the LiPo for an supercap then
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That is a nice setup, too… I’ll start experimenting next week : )

did you order some sun ?

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Not yet. I want to checkout the stuff sold by local dealers first.

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