How to select board for wireless transmission?

[larsdenmark]

Hi

I have been commissioned by my wife to create a wireless measurement device that can measure soil moisture, temperature and light intensity at various locations in the garden. The measurements should be transmitted back to the house for viewing and storage every 5-30 minutes. The device has to be supplied from a battery. I don't mind changing the battery every other week.

My current "expertise" is at Arduino level and I can also program for a raw Atmel MCU. I have the analog electronics covered, but I need some help for determining how to transfer the signals wirelessly. There may be need for 5-10 devices at a time. The garden isn't big, but I can't reach the far end of the garden with WIFI so I need something better. The distance covered is 20-30 metres.

Do you have any ideas of what technologies will be best? I value ease of use and availability of parts and programming environment over price.

I think that a Raspberry Pi may be suitable for getting the data (with a suitable receiver). The Raspberry Pi can then store the data or transport the data to another computer later. What should I look for here?

Thanks!

[Mr.B]

There are a multitude of 315MHz and 433MHz transmitters and receivers around - cost peanuts.
Example from first quick search on ebay: https://www.ebay.com/itm/5pcs-433Mhz-RF-transmitter-and-receiver-kit-for-Arduino/381374427148?epid=2037463354&hash=item58cbaff00c:g:8wEAAOSw6EhUN9s-
USD 2.88 for 5 of them. (No affiliation with seller - first search hit.)

I have used these type of transmitters and receivers numerous times.
They are cheap, however generally only good for short distance (100m) and definitely only slow data rates.
Your application would be fine with slow data rates.

Google: 433mhz rf transmitter and receiver arduino code

[larsdenmark]

Thanks!

I have ordered a few of these things from a local supplier. They should arrive tomorrow!


Lars

[mdijkens]

I'd use an ESP8266 for that
Waking up every 70mins it can run 1 year on a 18650

See one of my small projects here:
mdSensor schematic
Running in my boat, charging the 18650 once a year

[C]

Arduino level can be more then just Atmel MCU's these days.

You have arm based
STM32F103C8T6 ARM STM32 Minimum System Development Board Module For Arduino Micro USB controller ARM Learning Board
You can get this from many places
Alliexpress has this for $1.79
With compute power like this you can do more.

You can use ESP8266 & ESP32 with the Arduino IDE

Here you have a powerful CPU and WIFI radio.
Here you can gain Over-The-Air programming which can be nice for updating the program on the device.

The ESP32 has some advantages over ESP8266 which could be nice to have.

As to WIFI range like all radios it is a function of antenna & line of site.
Some videos on youtube where this was tested/checked.

With a good foundation you can do more easer. A part of this is having the CPU resource to do more.

Think
An Atmel CPU can do the job, but you have to connect to it each time to program.

Some will think an ESP8266 & ESP32 are over kill here. but you will have a lot of options that you can use to make total thing better.
I could see where being able to have simple touch sensors could make it nicer. Remember that touch sensors can be under glass or plastic.

[Buriedcode]

Why do people always jump to ESP8266 or WIFI modules for transmitting a few bits every 10 minutes?!  Sure you can power it down afterwards, but its overkill.  Whilst you could do the maths to calculation power budget for ESP8266 - its faster over-the-air-rate means its powered up for less time - there's also the time it takes to connect to the network.  Yes, using the ESP8266 allows for two way communication, over-the-air updates, and direct interaction via a webpage, but if one is making 10-20 of these things *just* for measuring small sensors the cost will add up, and they will drain batteries.

Any 8-bitter will do - Arduino just seems to be the most accessible, and some $2 433MHz Modules, which can be powered from an MCU IO.  The only downside with Arduino's is power consumption.  If you use a stock Arduino its regulator will eat power, and it generally isn't geared for low-power, but you can put the MCU to sleep.  An Arduino pro mini with the regulator jumper removed would probably be the easiest and cheapest setup.

[mdijkens]

but if one is making 10-20 of these things *just* for measuring small sensors the cost will add up

I buy my ESP-12E's for $2 a piece.

In my eyes it only makes sense (pricewise) if you've got a below $1 alternative...

[C]

Think this video addresses the radio differences & power use.
#172 Hidden: ESP32 and ESP8266 point-to-point (ESP-Now): Fast and efficient. Comparison with LoRa