Solar-powered weather station

That is definitely the way to do it Dave. I made some tests with a Wemos and a SHT30 shield, if you mount the SHT30 too close to the Wemos you get skewed readings. I overcame this by using long headers to mount the shield and using deep sleep between measurements.

BTW it is possible to calibrate / check humidity sensors relatively easily using saturated salt solutions. If you, or anyone else is interested drop me a PM with your Email address and I can send you the PDF file containing humidity values for various salts and temperatures. I cannot upload it here.

Here is a site explaining the process:


I read about humidity testing with salt a while ago when I was checking my 5 different sensors, but never got round to it. However, that article looks very easy and an interesting thing to carry out.
Thanks for the pointer Garry

Nice, you'll find some of my examples dotted about the forum as screenshots. Here is a sample from one of my dashboards:

That is.... Totally Information !

1 Like

I Like the BMP/BME-280's, the originals are from Bosch and they are both pretty accurate. I don't like that it is very hard to remember which is which.

  • BMP280 = Temperature & Pressure
  • BME280 = Temperature & Pressure & Humidity

I've a feeling that there might be a 260 range as well that doesn't have the pressure sensor.

Another nice sensor for temperature and humidity is the HTU21D, AKA SI7021 around the same accuracy as the BME280. These are the ones I mainly use now. Certainly avoid the DHT-11/22, etc as they are absolute rubbish, they are wildly inaccurate and drift over time.

When reading altitude, you must realise that this is calculated and not direct from the sensor which reads pressure. Note that, like humidity, altitude calculations are temperature sensitive because temperature changes the atmospheric pressure (some basic physics is always helpful!).

When measuring any of these things, do remember that while the sensors may claim "0.1% accuracy" and so on, that is really rubbish. You can get pretty accurate absolute temperature readings but humidity is massively sensitive to all sorts of environmental factors and a simple sensor with no mechanical airflow control will be lucky to get a reading within 10-20% absolute.

That is temperature only of course and generally comes in a waterproof housing. I have a couple lying around but I've never got round to using them "in the wild". Should be as accurate as the BMP/E-280 if not very slightly better because of the packaging.

The problem is that it is quite open so you would need to put it somewhere well sheltered to keep water off the sensor, I imagine that dew will impact the life and readings of a BMP/E-280 as well. Nice idea for the temperature readings though, clever.

I recently brought a rather nice rotary tool (like a "dremel") in an Amazon sale - under the Tacklife label, really well made and surprisingly useful, it would be ideal for making those kinds of projects.

This is quite common with many sensors. The way around it is not to over-read. Keep it powered off until needed, give it a second to get going, make a reading then turn it off again. Very little point in doing readings more than once a minute anyway, indeed once every 5 minutes is generally more than enough.

It absolutely does, humidity calculations are very sensitive to temperature as you can easily measure for yourself.

Yes, see my comments above.

You've got it :smile:

Yes, this is why the Wemos DHT-22 board is doubly useless.

I was really making reference to some of the dodgy packages out there. I have had two fail within six months of use in "suspicious" circumstances. But I'm sure the sensors themselves do exactly what is stated in the datasheet.

Well, that's school holidays almost over. Looking forward to some updates.


1 Like

Any updates, its all gone quiet.

Hi Martin,
I had a set of IN219A current/voltage sensing devices arrive this morning, so my (weather station) student will have the task this week to incorporate one of them in his circuit.

I'm going to try it out one of them on one of my own circuits tomorrow (just to make sure there are no problems).

Thanks for your continued interest in the project.

Regards, David.

Well, I'm home after 7 weeks away at work.
Time to play.
How's things coming along with the weather station?


Hi Martin,
Welcome back (home).

Lashed-up one of the INA219 sensors on a spare breadboard - worked like a dream with a Wemos D1 Mini.

The weather station is on hold at the moment as the school has an Open Evening towards the end of September and my students have offered to run some demos of their work within the Club to prospective parents.

I've also taken on a new set of students (as this is the start of a new school-year) so I'll need to start from scratch with them.

Thanks for your continued interest in the project.


So, what you thinking of for the new students ?
Just building on what the others did.

I have a lot of work to do on mine, lot of re-coding and change some sensors. Things haven't been too reliable while I have been away.
Here's an updated link.


My word that's an impressive dashboard.

My plan (for the new students) is to start at the beginning...

  • Health & Safety
  • How to logon to the Club's private network
  • Using a breadboard
  • Building your first node to control an LED from Node-RED
  • etc...


I suppose then it will be a while before we see them getting hands on and building another weather station or adding to the existing, or do you have other projects in mind?

I have some ideas in my mind and some 'spin-offs' (remote communications) from the weather station project that I've developed with Paul @zenofmud

One of my students wants to set-up a VPN so he can check the IP cameras at his home and see if the postman has delivered anything for him.

Here's a test circuit for the INA219 (voltage/current) sensor.
I've used a 330 ohm resistor to lightly 'load' the circuit.
Before tearing down the circuit and incorporating it into the weather station (i.e. to sense the solar panel's output voltage and the current flowing into the TP4056) a Fritzing layout was produced.

The Fritzing image was produced and sent to me by @zenofmud - thanks Paul.

Here are some screen-shots from the Wemos D1 Mini (running ESP Easy).


Was a bit confused with the circuit diagram at first. I thought you had wired it up strangly, then I read you text again and realised the 330R was just to test it.
Funny, I have an INA219 and not even got around to useing it yet. I also got hold of an INA3221, which is a 3 channel version.
However the 3 channels are not independent, they all run from a single supply.
As I will (eventually when I get round to it) have multiple sensors in different places, I will probably feed them from the INA3221 and be able to measure the current/voltage for at least 3 seperate sensor nodes.
Unfortunatly since coming home from work a few weeks ago, for some reason I just cannot get into it.
I need to crack on and get things sorted.
I now have a lightning sensor which I am having difficulty interfacing. I wanted to use it with an ESP8266 but there are no libraries, so need to run it from and Arduino and then link it the the RPi running Node-Red via some other meathod, maybe bluetooth.
I also need to re-do my particle sensor, I have some different code to try with a library, at the moment its running without a library and just straight code.
Catch you later

Hi Martin @Cathprotech,
I've written a tutorial guide for my IoT students on how to use the INA219 voltage/current sensing device.

Here's a hyperlink to it.

INA219 - voltage and current sensor

Hi Dave,

Looks good but I can only see one error and its a big one.... where is the 'Sun' thing you mention? Measure light levels from what?

Well, I'm back at work for around 28 days so cannot do anything and unfortunatly on my 5 weeks at home I was messing around with a lightning detector and didn't get much else done. I did connect a couple of small 6v 1w solar panels up to a Li-On charger via the INA219 and monitored that for a few days.
I noticed even in strong direct sunlight, the maximum current I could draw was just over 120mA at 4V (around 400mW) and that was from 2 panels connected in parallel.
It took 4 days to top-up a 2600mAh Li-On battery to full charge, starting from around 3.7 volts.
How is the project coming along Dave. Did your students manage to build the circuit with the INA219 and find the sun?
What sort of results did you get?