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Triggering problem on cDAQ-9178

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I am trying to trigger my cDAQ-9178 on the chassis PFI0 line.  My digital input, unfortunately, is not 0-3.3V, but rather the low state is at 1.6V and the high state is near 5V.  Using this trigger source, the cDAQ does not register the trigger at all.  I'm assuming I need a pull down resistor to bring intermediate level to low.  I'm wondering if there is a way to this programmatically on the board itself, rather than using an external resistor.  I know some devices have this option, but I'm not sure how I would do this on this device.

 

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Accepted by topic author speclabAI

Unfortunately, you need an external signal buffer to translate your 1.6-5V signal into a 0-3.3V signal.

 

santo_13_0-1675135177954.png

 

The easiest way is to create a 1:1 voltage divider using two 10k resistors, now your 1.6-5V signal becomes a 0.8-2.5V signal (maybe on the border of the specifications)

 

 

BTW, where do you get this weird 1.6-5V signal from? that seems odd.

Santhosh
Soliton Technologies

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Hi,

 

Thank you for the suggestion.  The signal is a digital out from a PI piezo stage.  I agree it's odd that the signal is referenced to 1.5-1.6V, which makes no sense to me.  I emailed PI and asked them if this is how the digital IO is supposed to operate - the manual simply refers to the outputs as TTL, which should be 0-3.3V.  A divider may work, but, as you say may be just on the edge of the specs and I'm afraid I could lose triggers this way.  I suppose I could also configure something where I use this source as an analog trigger and a counter to generate the digital trigger.  Once I hear back from PI, I will update the post in case anyone else has had a similar issue.


Thanks

 

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