Robust electronics advice

Hi everybody!

This is my first try at developing an Arduino project… I hope I've not done something terribly wrong.

Long story short, it's a RS485 connected Arduino reading data from an 1-wire digital sensor and an analog phototransistor. I have completed the software and it works fine, now i would like to deploy it outdoor.
I will use an arduino Micro, but I have placed the Uno version in the breadboard to make it more readable.

12V power comes from the RS485 line, that's just a standard 1A switching power adapter.

The Arduino itself and the electronics in the bigger breadboard will go inside the main case, while the components in three smaller breadbards will be "satellites" connected via some a few meters long wires.

Now, the question: I do not know why, but I have a feeling that I should add more electronics to protect the Arduino before sending its output into a long outdoor wire… could you please give me some advice on the topic?

Also, what kind of case would you suggest me to use? Maybe an IP68 white plastic case to protect it from heavy rain? Or it is better to use a ventilated case to avoid overheating under the summer sun?

Would you use shielded cables? And, if yes, how would you wire the shielding?

Thank you!

Electronics on a breadboard is not compatible with your goal of making it robust. Get yourself a soldering iron and some stripboard or protoboard or order a PCB and solder it all together once you've gotten past the prototyping stage.

I thought this was a good article:

The Arduino won't generate enough heat to need ventilation, you need a well sealed case to be weatherproof,
you don't want moisture getting in.

RS485 will give you the ability to have a long cable run without problem (limited by the voltage drop
across the power and ground wires).

However there is a risk from thunderstorms - nearby lightning could be bad news, and the main protection
against that is opto-isolation which can't work for a wire delivering power obviously.

However its a rare occurrence I think, a risk you can live with?

pert:
Electronics on a breadboard is not compatible with your goal of making it robust.

I didn't explain myself, but this is just a prototype, the deployed version will be on PCB.

I thought this was a good article:
https://www.digikey.com/en/articles/techzone/2012/apr/protecting-inputs-in-digital-electronics

Thank you! This is a very good article indeed: I will try to calculate the correct values and see if it works for my prototype.

MarkT:
However there is a risk from thunderstorms - nearby lightning could be bad news, and the main protection
against that is opto-isolation which can't work for a wire delivering power obviously.

However its a rare occurrence I think, a risk you can live with?

Well, I am planning to run the 485 cable underground or laying on ground, so I hope that will reduce the lightning strike risk. The shorter sensor cables will be running on the air instead, I could power the sensor straight from the 12V line using a 7805 and opto-isolate the signal pin, but will it work? Or will it just catch spikes and send them back to the Arduino through VIN?

Hi,
Do you have a schematic of your project that you can post.
Please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

The fritzy tells us nothing about which component is which and what the pins are.

Thanks.. Tom.. :slight_smile:

You wrote the power comes from the RS485 line. I wonder how that works? quote: The RS485 signals are floating and each signal is transmitted over a Sig+ line and a Sig- line.unquote. There is no ground and the voltage on the signal wires is bipolar.

Is there something you didn't tell us?

Paul

On ground or underground doesn't reduce the risk of lightning strike. If your wire connects two buildings then a lightning strike near one of them can raise the ground potential hundreds of volts. That will go down your wire and come out somewhere in the other building.

If you have correctly-protected cable entries, that should be where the extra energy is dissipated.

Make all your sensors plug-in so they can be easily replaced. Looks like you have a humidity sensor. I have read they have a limited life time.

Paul