Couple of hardware interface questions

I am new to Arduino and am working on a small project intended to read commands sent from a LANC video camera controller and to appropriately trigger an external digital video recorder when I press the REC/STOP button on the LANC controller. I have two hardware-related questions:

  1. The external recorder docs say that the external trigger needs to "connect pin x to pin y" (pin y is ground) of the external trigger connector in order to trigger the recorder. This suggests to me a relay, but I would rather avoid the extra component. I am guessing that the trigger sense circuit inside the recorder really just needs to see pin x pulled to or near ground, but I don't have enough experience with electronics to be sure. I am tempted to just try using a digital pin of the Arduino to pull down the appropriate line of the recorder to see what happens. Am I missing something that makes this experiment a bad idea? The recorder is rather expensive, but I am less worried about the Arduino. If it is important, I am using a Uno for prototyping and will build the final device using a Nano.

  2. The LANC specs call for the master device (a video camera, in my case) to provide +5V on one of the three lines. I can't find any information on how much current this line can source, but I know that it can power LANC controllers. I intend to detect whether this is present as one of my status checks that will condition whether a "ready" LED is lit. My plan is to simply connect the 5V signal to a digital pin and read that pin to determine whether the 5V is present. Would it be good practice to place a current-limiting resistor or some other protective device on that pin?

Thanks for your help. And thanks also to the many others who have posted LANC-related information and Arduino-based LANC projects. Getting my code running was insanely easy for a complete noob as a result of all of those efforts.

I am tempted to just try using a digital pin of the Arduino to pull down the appropriate line of the recorder to see what happens.

Resist temptation until you have at least measured what voltage is on that pin. What you need actually is a FET to act as a voltage variable resistor, connect the gate to the arduino through a 470 ohm resistor, the drain to the recorder and the source and two grounds together.

Would it be good practice to place a current-limiting resistor or some other protective device on that pin?

Yes I would start off with a 330 ohm one.

Thanks, Grumpy_Mike!