Hello. I am a scientist and I need to monitor soil moisture and temperature for the lowest cost possible. Moisture and temperature needs to be recorded at a depth of 25cm from the soil surface. Sensors need to be installed in 4 remote forests. I can only visit the forests 1x per month to get the data. I would like continuous data collected perhaps 4 times daily for the month. I would like to do this year round, but could remove if freezing would damage sensors. These are forests so solar for powering units is not possible.
Are you certain this isn't just an assignment in your computer class? Scientists obtain their title by showing originality in their field.
Forests do not have sun? Do they grow solely from the "fertilizer" of "scientists?"
What value do you place on your time? Commercial sensors are available for what you describe, and are quite inexpensive, in comparison with the effort you'll put into rolling your own. Particularly if your data requires calibrated, accurate sensors, which is almost always a prerequisite for a scientific effort of any worth.
The depth of 25cm rules out the sensors we commonly see, not sure how that will be accomplished.
You will need a battery that will last a month regardless of temperature. You say continuous but changing the battery may break the monitoring.
You say continuous data then say collected perhaps 4 times daily. Does that mean you will come to collect the data?
I have extreme doubt this can be done at all, and certainly not cheaply. Most common batteries do not perform well in the cold or extreme heat so you may need a very large battery that will probably get stolen.
"Soil moisture" is quite vague from scientist. What are you actually planning to measure?
Let's start by getting a few numbers.
- How many units in total?
- What is the outside temperature range?
- What units of moisture are you measuring?
- What is your budget for parts? "Lowest cost possible" is not a budget. You need to decide what you can afford or you're possibly wasting time.
- I assume that you plan to build these yourself? Otherwise you will need a development budget in addition to a parts budget.
Other:
- Minimum storage of 4x31 (124) samples before retrieval. Perhaps bump that to 4x62 in case you can't make it out there for two months.
- Solar power is not feasible. Do you have limitations on battery type?
- Do you need to record the time of day that a sample is taken?
- What is the environment like? Rainforest? Dry? Humid? Flooded area?
- Does it need to be protected against large animals like moose or elephants?
Sorry. I am new to these forums and should have been more specific. I was hoping that someone could provide information on what arduino products could do this along with the code. So the specifics that would be appreciated are: What sensor, cord, and circuitboard to use. The code would also be very helpful (e.g. code that would tell the sensor to record at specific times (I can change these in the code after so someone could just make up some as placeholders, and then tell the sensor to store data too SD card (or other)). Thank you in advance.
4 total units. Temp range -15 to +25 degrees C. I am not sure of the moisture units, so that is flexible. Budget can be flexible but until $200 would be preferred. Yes, plan to put together. Your other suggestions are good too. Definitely a battery smaller than deep cycle marine. I would assume the code tells the device the time to take it? Yes, I would select several times. Temperate ecosystem. No protection needed. Thanks. Hopefully you can suggest the products based on this. Much appreciated.
The simplest path forward, hardware-wise would be the Adafruit Feather RP2040 Adalogger - 8MB Flash with microSD Card [STEMMA QT / Qwiic] : ID 5980 : Adafruit Industries, Unique & fun DIY electronics and kits
It has an SD card interface built in for data storage, a LiPo battery charger, and a real-time clock.
Temperature sensor is easy to add, but you'll have to decide exactly what you mean by "moisture sensing."
A probe to go 25cm into the soil will have to be a DIY effort.
You will need to write software for logging, but if you aren't ready for that, there's the "Jobs & Consultancy" forum for paid requests.
If that is your most important requirement, the project is doomed to failure from the very start.
You can buy very cheap equipment, put it out in the woods, then come back a month later and find that some of it failed to even start, let alone finish the job.
Try to put some value on actually getting the data that you want.
If you want repeatable time of day measurements, you'll want something with a Real Time Clock; if each data record will be date, time, and two or three floating point values, then your storage need will be several kilobytes per month. These all will constrain your choices.
I would hope a scientist knows where to find field-related data.
Just for fun: