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Author Topic: Contact Closure Input module.  (Read 666 times)
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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 smiley

Thanks.

* Diagram-Model.pdf (17.42 KB - downloaded 26 times.)
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What do you mean by 'dry contacts'?
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What do you mean by 'dry contacts'?

Short circuit between com and input, "DRY" as with no voltage
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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' ?
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No external voltage
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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..
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I actually have no idea what you mean.
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