Description of the article

This article contains a quick demonstration of how to use or test the functionality of the digital out on Krypton-8xDO 8xDI.


Description of the solution


In the picture below is a connection diagram on how to use the digital output and directly connect it to the digital IN side:




There could be some issues with a voltage drop if DO is used for triggering external devices and simultaneously detecting the trigger on DO with the DI channel on the same device. The reason for the voltage drop is because the Krypton-DI has a lower impedance than an ACC for example. 



The graph below shows the difference in the current if the voltage is changed between DI+ and DI- pins:



The blue line is voltage and the green line is current. 

So if different pull-up resistors are used the voltage drop also changes (the results were tested/measured on the 5V power supply):


  • 1 kΩ = 2V drop
  • 460 Ω = 1V drop
  • 220 Ω = 0,6 drop 

EXPLANATION:

If a 5V power supply is used and a 1 kΩ pull-up resistor this results in a 5 mA current which either flows through the DI input or it flows through the DO internal switch (pull-down). 

The problem is that the internal DI is made as a current sink with >5.3mA requirements for the DI input to work normally. 

So the 1 kΩ resistor is not suitable because there is not enough current. If it is reduced to 460 Ω this increases the current > 10 mA so that the DI really switches as it should. 

The voltage at DO1 pin1 will never be 5 V but will be somewhere in between (because a constant current of approximately  5.3 mA flows across DI) or it will be almost 0 V in case if DO is activated.


Additional information