Output circuit for cRIO 9477

[d4nvjpl0ng4n]

Hi all,

I am trying to use output of cRIO 9477 (Digital output module) as the digital input of Arduino Mega 2560 Board. I will use 8 outputs of 9477 as 8 inputs respectively and use the external voltage is the 5V output built-in on Arduino. I don't know how to make the circuit in oder to connect them together. 

I need your help. Thanks in advance

[AndyClegg]

It isn't clear if you have tried connecting and it isn't working, and what exactly it isn't doing. Not knowing how familar you are with the software programming side of things, do make sure its not a software issue on either device by measuring the Digital outputs / setting the digital inputs in isolation from each other. You understand the concept of sourcing / sinking IO to make sure they are compatible with each other and have the wiring correct depening on where supply and GND are. This explains the basics of that http://digital.ni.com/public.nsf/allkb/A10122C63A7F5CFE86256B4C007491DD - but you will need to read the manuals of both devices to check.

[Larry_Morgan]

The 9477 is a sinking only digital output (similarly known as common drain or common collector). To use this, you will need to connect suitable pull-up resistors between the +5V supply provided by the Arduino and each of the digital inputs. If the Arduino already provides pull-up resistors, then this step can be avoided. 

Then you connect each of the digital inputs to a DO pin on the 9477. Lastly you must connect the 9477's COM terminal to the Arduino's ground. 

When an output on the 9477 is logic high, it will be high impedance, and the pull-up resistor will cause the voltage to be +5V. When the output of the 9477 is logic low, the sink is enabled, which will pull the voltage down close to COM/GND. 

Some other things to consider:

1. Make sure your Arduino's digital inputs can tolerate the +5V provided. 

2. Pull-up resistor values will depend on many factors. A primary factor is the amount of current the +5V output of the Arduino is designed to provide. A higher resistance will lower current draw, but a lower resistance will decrease rise time and allow faster switching. 

3. The 9477 can tolerate 1 amp per DO line, and 20 amps total per module.