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Question about the operation between sinking type output and sinking type input devices

Hi all,

 

I have NI 9478, NI 9474 and NI 9426 module. I have tested the operation by connecting each other. 9478 is a sinking output module, and 9474 is a sourcing output module. 9426 is a sourcing input module.

 

If I connect 9478 and 9426 and set True to 9478 in LabVIEW, 9426 also read this signal as True. Up to this point, it is considered normal operation. However, when 9474 and 9426 are connected, 9474 is read as False when 9474's output is True, and 9426 is read as True when 9474's output is False. Is this the right behavior? Since the sourcing output and the sourcing input devices are connected together, a pull-down resistor is applied to the digital signal line. I also uploaded the hardware wiring diagram that I used. (Red is Vsup Node, and Blue is GND. Green line is digital siganl line.)

 

Connection between NI 9478 and NI 9426Connection between NI 9478 and NI 9426

 

Connection between NI 9474 and NI 9426Connection between NI 9474 and NI 9426

 

 

There is little experience with digital I / O interfacing. I wish I had someone to help.

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Message 1 of 8
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Hello,

 

Here is an article that explains the ways you can connect 2 sourcing devices: Connecting Two Sinking or Sourcing I/Os.

 

According to this article, I would check the size of the pull down resistor you are using.

Niki Budgell | Product Planner - SW Management | NI
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Message 2 of 8
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Hi Niki, 

 

Thanks for your reply.

 

I already read that article and used the suggestion. And if the resistor size was not adequate, then the Boolean signal would not have been delivered to the C series input module.

 

Could you guys test the C series modules like my configuration? It's kinds of simple thing, so I'm sure you will be able to confirm it soon.

 

Thanks.

 

 

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Message 3 of 8
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Hello,

 

What size resistor are you using?

 

From my understanding of the article, we need to match the size of the resistor, so that when the digital output is off (0), the digital input is reading a low (0) as well. 

Niki Budgell | Product Planner - SW Management | NI
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Message 4 of 8
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Hi,

 

I'm using 50k resistor. 

 

As I mentioned earlier, I think that if the resistance value is not right, signaling will not be delivered at all, or that signaling will not be consistent every time it is operated. However, consistently, when the digital output is turned on, it is read as OFF, and when the digital output is turned off, it is read as ON. Therefore, I don't think it is a matter of choosing the resistance value.

 

Thanks.

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Message 5 of 8
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Hi,

 

Before looking for solutions one question: Why do you want to connect a sourcing output to a sourcing input ?

Beside the fact that you may not have any other modules.

 

Kees

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Message 6 of 8
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Hello,

 

I was verifying the operation of the module with the above three modules. The sourcing input and the sinking output operate as expected. When the sourcing input and the sourcing output are connected to each other, the operation is opposite to what I thought.

 

I would like to see if this operation is the cause of the product failure or if I wrongly configured the hardware.

 

Thanks.

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Message 7 of 8
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Hi,

 

For testing the devices you can use this. And your devices are working as I would expect.

I made a (simple) drawing of the outputs and input. Let me know if you understand what is happening.

As you can see if you connect the 74-out to the 26-in the 'signal' is inverted.

 

With either sinking or sourcing inputs and outputs I would use a switch and a LED for testing these devices.

 

Kees

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Message 8 of 8
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