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If you're open to a more mechanical solution, I'd suggest building a "tipping bucket rain gauge", best explained by a picture (source: https://www.researchgate.net/figure/Sideview-of-tipping-bucket-Rain-Gauge_fig4_304297354):
This should be relatively easy to build and it's trivial to read this electronically by detecting the time it takes to tip. ...
13
Upon reading the question my first thought was, please define what is meant by "how hard is it raining?".
My initial tangent thought was "what about the impact energy of the rain" - heavy rain can be felt. Anyone who has heard rain fall on a metal or poly-carbonate roof will know the difference in noise produced by light and heavy rain.
...
12
It's not perfect, but a simple solution to the issue of a puddle building up on the resistance plate is to tilt the plate a bit, so that instead of the water building up on the plate it runs off. Your device would then look for sudden drops in resistance, indicating that a droplet has formed on the device, followed by the resistance rising again after the ...
12
One way to do that is to estimate how much water is changing. If you can ignore the spill over, then that is approximately how much the puddle is changing.
Another idea you can use is to measure the changing weight of a rain gauge (that will need to be emptied daily, unless you can rig something that will do that for you). The faster the weight increases, ...
10
The WMO report Instruments and Methods of Observation has a chapter on Measurement of humidity and a separate chapter on Measurement of upper-air pressure, temperature, humidity. The first deals with instruments used for surface measurements. The second deals with instruments used for measuring vertical profiles, which have to deal with a larger range of ...
9
I've built DIY conductivity probes for subglacial measurements. Unfortunately my sensors remain under ~100m of ice so I haven't be able to recover them to check the calibration, but for the same reason, I've taken multiple measurements to reduce calibration drift, as I'm unable to re-calibrate them. So far, they have produced sensible data for 2+ years, but ...
6
We use something like an Onset HOBO electronic sensor. They've got logging (and in some cases, networking) built in. They'll typically log both temperature and relative humidity at regular intervals specified by the user.
Humidity sensors have a tendency to wander off calibration, so you will need to take that into account when designing your monitoring ...
6
Edit: 1 May 2021
The following procedure uses the less accurate method from page 455 onward from the scanned sections of the book pictured below, from the original answer.
The procedure is a multistage process ideally suited to either a spreadsheet or programming code.
The equations use SI units.
1. Calculate the saturated vapor pressure at the dry bulb ...
5
I would approach this by counting pings on a plate with an attached piezo or microphone. The amplitude of the ping will give the volume of the drop and the number of pings the drop quantity. This is a more robust real-world interface than an electrode sensor.
5
A 'video disdrometer' is a device for characterizing raindrop size distributions. Professional versions (e.g A 1D distrometer) can use a video camera to image the shadow cast by water droplets moving in front of a bright light. So one DIY approach might be a camera imaging rain drops falling through a gap.
Delft university have put up an instructable for an ...
4
Accelerometers, preferably triaxial (i.e., those that record horizontal and vertical motion). Beyond that your question is indeed a bit too open-ended. Some use many cheap MEMS (http://onlinelibrary.wiley.com/doi/10.1029/2008GL036572/epdf; https://www.theverge.com/circuitbreaker/2017/7/13/15963996/raspberry-pi-seismograph-early-warning-earthquakes; these are ...
4
I sort of accidentally did this in one of my projects in a complicated, backhanded sort of way.
I installed 16 soil moisture sensors in my yard as part of an attempt to track the distribution of water in the soil of a flower garden.
The sensors are battery powered. They transmit their data via Bluetooth Low Energy to a couple of WiFi enabled control nodes in ...
3
You could connect a funnel to a water wheel.
The faster it spins the higher intensity of the rain.
This sensor was selected randomly, as should not be consider something I specifically endorse.
https://usa.banggood.com/TZT-5V-Piezoelectric-Film-Vibration-Sensor-Switch-Module-TTL-Level-Output-Geekcreit-for-Arduino-products-that-work-with-official-Arduino-...
2
The Bureau of Meteorology in Australia traditionally uses wet and dry bulb thermometers read by humans, when measuring temperature. However, for remote automated weather stations, electrical equipment is used. The dry bulb temperature is measured using a resistance temperature device (RTD) and relative humidity is measured using relative humidity probe.
The ...
2
I misunderstood how wet bulb thermometers worked and was confused too... and I'm hopeful that explaining my separate confusion will actually help put emphasis on what's really happening for your question too...
I always was taught that as a sling psychrometer was spun, water would keep evaporating by taking heat from the thermometer, and it would keep doing ...
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