Check continuity - Nc contacts

Hi to all. i would like your opinion about a setup i am thinking to do...

Prologue : There is a 3 phase motor that drives a long belt in a facility. There is a small control with a pcb that drives the motor.
The belt function has two safeties, The first one is with two switches at the ends that working as terminal switches (left limit and right limit), The second one is a Stop/kill switch.

i thought a design in order to monitor the safeties (just monitoring them ) so when the machine is stopped and i am not there i can log in to a server that arduino had send the state of the safeties through a gprs (sim800L module)

here is the diagram how the setup is right now :

some extra information :

  1. The switches using 110v ac as signal input to PCB .
  2. The grounds are not connected to the physical ground... the grounds in the metallic cases of the switches are connected to the coil of the Relay in the Diagram so when there is a shortage to the case the relay works and cut the electricity to the pcb.

Here is what i am thinking to do :

In the main pcb in the two safety inputs i would take a parallel cables and connecting them to my arduino setup . it is just a simply voltage divider with a 4.5v zenner diodes for Arduino digital input . (i havent added the Sim800L connection in my diagram )

My Question is (and here is that i want your more experienced opinion) , can you spot any feasible dangerous? can my arduino setup interference with the main circuit ?

What i would avoid is if for some reason the end limits or stop is activated and because of my arduino setup the main pcb reads that the stop is NC and keep driving the motor..

any thoughts would be welcomed

thanks in advance

I don't think you have a correct schematic to start with, your step relay coil is connected to 110VAC on one side and ground on the other. As there is not (does not appear to be) any connection between either output of the 110V transformer and ground the circuit for powering the coil of the step relay is incomplete.

In the block PCB micro-controller you show out 110VAC but there is no indication of which of the 2 AC input connections this comes from, so impossible to know for sure what is going on.

As the 110VAC is not (does not appear to be) grounded at any point you have to be sure you are not grounding it anywhere, for example through your PC and USB cable when programming.

You need to be careful with terminology here as 'ground' is ambiguous here, it could mean 0V, it could mean the chassis of the machine and it could mean safety earth.

You show your project powered with a battery, how long do you need the battery to last and have you considered the power consumption and intended battery capacity?

Please re-draw your schematic to clearly show the connections and review how the step relay is connected, and distinguish what ground really means.

That you are asking and show such simple errors makes me worry that this is a dangerous project too far outside your skill level. I think it is unwise to ask for advice on safety critical projects on a forum on the internet with strangers of unknown skill giving advice.

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Thanks for the tips.. my mistake not telling that i am not from a country that speaks English so some times trying to describe something and trying to guess what is the terminology in English is little rough.

some extra explanation :
The transformer has input terminal (230v ac) and out put terminal with 0v , 110v that goes to pcb.

The relay (110v ac coil) is connected to the 0v in one side of the coil and the other side in what i am drawing as a ground in my schematic. The pcb outputs the 110v as a signal to pass through stop and terminals switch contacts and read it then as input the pcb's microcontreller . All switches are mounted in a metallic cases.
so if for some reason the 110v is shorted with the metallic case the coil of the relay gets the 110v and so arms and cut off the power to the pcb. I think it is an extra safety for the case if the 110v is shorted not bypass the switches and so the pcb gets signal if the switches are in Normally Opened position

No i am not attend to use a battery for that project, my mistake using this part in fritzing. the arduino will be powered by a power supply adapter from 230v Ac to 9v dc.

Also i never program my projects during are connected to the circuits.. i like to make them detachable so i can remove them, program them and then reinstall them

Your English is fine.

However, your schematic is not fine, there are problems with it as I mentioned. The language of electronics is the schematic, not words. Please don't try to correct the schematic with words, instead please draw a new schematic to reflect the actual circuit accurately and post that. Frizing is not a good tool for schematics, have a read of this: How to make a schematic you can post..

Thank you.

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