Transistor output question

[joel7269]

I'm trying to use the output port of an AXIS Camera to trigger an event on my elk m1. I don't understand the transistor output (pin 4) in the AXIS instructions where it says to use a diode in parallel. Below is from the axis m1054 manual explaining ports. The input port is easy the output just doesn't make since and I don't want to hurt the camera or my Elk. If I was to use a 912 relay would I still need a diode? I'd also be interested in going directly into a zone on my elk panel and use non-alarm and then create an event.




Function | Pin | Notes
------------------------------------------------

GND | 1 | Ground​

3.3V DC Power | 2 | Can be used to power auxiliary equipment. Note: This pin can only be used as power out.
Digital Input | 3 | Connect to GND to activate, or leave floating (or unconnected) to deactivate.
Transistor Output | 4 | Uses an open-drain NFET transistor with the source connected to GND. If used with an external relay, a diode must be connected in parallel with the load, for protection against voltage transients.

 

[BLH]

When you turn Off the external realy that has an inductive coil. It can generate a high voltage pulse. The pulse is reversed polarity from the voltage applied. So the diode conducts when the output turns Off. Protecting the NFET in the camera.
It looks like the ELK912 has a diode on it.
Someone maybe able to verify the relay has a diode already so you would not have to add one.

 

[gatchel]

The instruction sheet on Elks website says:

Diode Protection Across Relay Coil

You should be good.

 

[joel7269]

Thanks for the help.

 

[BaduFamily]

Sorry for waking this thread - joel7269, how did that go?
 
I am thinking of connecting the output of an Axis camera ( P3364-L ) to an M1 input, and an M1 output to the input of the Axis camera...