Building a live CTD-like device

Hi,
I’m trying to concept a waterproof device that measures different parameters in the water and shows it at the surface on a screen. I’m very new to this field and would be very interested in your input and your experiences. What I planned is the following:

Using a dive light as a waterproof enclosure with Arduino + battery + sensors. These would be (from easy to more difficult/expensive to implement: Temperature, water depth (pressure), conductivity, light intensity and turbidity. Ideally I also want to add dissolved oxygen (expensive), pH (apparently not really reliably and not difficult for permanent measurements), and Chlorophyll a fluorescence.

All measured parameters will be sent via RS485 to another Arduino above the water surface (boat) which displays data on a Nextion display. Ideally it would add add GPS position of the boat and logs all data on a SD card. If possible, there’d be a button at the topside Arduino to start logging (but RS485 communication is only possible in one direction?).

-Do you think this project is realistically doable Arduino or would I need something like Raspberry Pi?
-Would there be a way to directly display data of the underwater Arduino above the water (without using another Arduino)?

Thanks for your input!

sojaman:
-Do you think this project is realistically doable Arduino or would I need something like Raspberry Pi?
-Would there be a way to directly display data of the underwater Arduino above the water (without using another Arduino)?

Doing all the sensor stuff and outputting '485 data is fine with an Arduino. If space is a concern then an Arduino Nano will be able to handle all that.

You couldn’t realistically directly drive just an LCD display down a cable. Sending RS485 data is the right way to go.

Displaying that data could be anything; another Arduino, a Raspberry Pi, a laptop with a '485-USB adapter.
You’d just have to write some software for it.

It would be quite possible to use some existing “Serial Terminal” software for a Pi (for example) and have the underwater Arduino format the data nicely for display on that terminal. Just means you have very little work to do ‘topside’ while adding complexity to the submarine Arduino.

Yours,
TonyWilk

Thanks for the input. I'd like to use 3.3V Arduinos to easily connect I2C sensors (both for topside and underwater). Does a normal RS485 board works with 3.3V?

sojaman:
Thanks for the input. I'd like to use 3.3V Arduinos to easily connect I2C sensors (both for topside and underwater). Does a normal RS485 board works with 3.3V?

Have a look at: RS485 communications

it mentions "3.3v RS485 Network" using the LTC1480

A lot of '485 is usually 5V

Yours,
TonyWilk

But I could also use a level shifter, right?

sojaman:
But I could also use a level shifter, right?

Yes, you could level-shift from a 3.3v processor to a '485 chip running on 5v (or the other way around)

However, it is not necessary.
If you have some 5v device, use 5v RS485 transceivers
If you have a 3.3v device, use 3.3v RS485 transceivers

... the signal pairs are compatible between 5v and 3.3v parts.

[ this is because '485 uses a differential pair of lines to send signals, the actual voltage levels on those lines only swing by about 1.5v - irrespective of the voltage the chip is running on ]

Yours,
TonyWilk