Safety concerns regarding external power supply connected to the TTL inputs of my 9401 card

[roto123]

I have an external power supply (5V DC, 500 mA) that I'm using to test the counting inputs of my 9401 card and verify my LV code is working correctly. The power supply +5V is used as the high signal, and the ground as a low signal.  I haven't made the connection yet because I wanted to know if there is any concerns with burning out my card.

[K C · Accepted solution]

Hi,

Normally, if everything is OK, it should not be a problem.

But in the real world 'things' happen 

My advise is to add a serial resistor (in this case of 1k) to protect your device if Murphy enters the room anything goes wrong.