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Topic: Contact Closure Input module. (Read 1 time) previous topic - next topic


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 :)



What do you mean by 'dry contacts'?


What do you mean by 'dry contacts'?

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


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' ?



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.

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