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WebDAQ 504 digital input wiring

Tobias Z


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The WebDAQ digital input is internally pulled up to +5v via a 100k ohm resistor. Assuming the relays is the dry contact type, it can only pull the digital input down to ground (GND) when it closes. When open, the input will return to +5v.  I'm sorry, but it doesn't provide a means to change the internal pull up to pull down and because of this, I don't see a way of reading a logic low with the relay contacts open. However, if you're looking to trigger the WebDAQ 504 when the relay is open, use rising edge as the type. This will force it to wait for the input to transition from low to high or from closed to open.

Best regards,


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Hello @Tobias Z.

There is no digital I/O diagram in the WebDAQ 504 User's Guide.  However, the bottom of page 10 shows a figure of the digital I/O screw terminal pinout.  The top of page 11 describes the digital I/O lines.  Via software, each bit is individually configurable as an input or output.


Are you configuring the digital I/O lines as inputs only?

What type of signal will you be connecting to the digital I/O lines?




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Hello @Fausto

I connected the relay contacts to the DIO 0 on the WebDAQ 504, but I only get a 5V (High) reading.
On the REST API Help (https://www.mccdaq.com/downloads/WebDAQ/REST-API/1.0.0/webdaq-rest-api.html#digital-information-digital-bit-get) it reads:


Bits intended to be used as input should be left at the power-up default value of 1.

But this results in a value of 1 (5V) when the relay contact is open or closed.
How can I get a 0V reading when the relay contact is open?


Kind Regards


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