Contact Closure Input module.

Hi everyone.

This is my first project, and actually first real experience with electronics.

My goal is to make a module that can accept 32 inputs that will trigger TCP commands.

in the attached diagram, i have under the "Inputs" both a "COM" and a "GND"
the MAX306 is a 16 channel multiplexer.

as for now if i input dry contact closures, i must connect them between the "COM" and the inputs.
That way the input passes the COM's voltage to the analog inputs.

If i want the inputs to supply external 20V i must connect the -(negative) to the "GND" and the +(positive) to the inputs.
Since i am using a resistor voltage divider the input stays under 5V.

As for now that works great.

My questions are,

1. how can i have it have a single "COM" that will accept both dry contacts or external 20V

2. If i can do the above, is there a way to have the external voltage wired both ways (either + to COM and - to the inputs or the opposite)?

3. What type of protections should i add?

4. Any feedback for improving the circuit?

5. I have noticed that printing Serial data delays the whole code(Every loop lasts about 1.5 millisecond when sending one string a loop) , is there a way to avoid this?

Later on i will add a voltage regulator to power the Arduino with the external power supply.

• At least i am able to make a nice diagram

Thanks.

Diagram-Model.pdf (17.4 KB)

What do you mean by 'dry contacts'?

Henry_Best:
What do you mean by 'dry contacts'?

Short circuit between com and input, "DRY" as with no voltage

Yarash:

Henry_Best:
What do you mean by 'dry contacts'?

Short circuit between com and input, "DRY" as with no voltage

The Com output has +5V on it. How is that 'with no voltage' ?

No external voltage

Place 5V out, the contact is shorted when 'on' and open circuit when 'off'.

5V ---- Terminal 1 --------
IP1 ---- Terminal 2 ------|

If my crude representation above shows it clear enough..

I actually have no idea what you mean.