Module Power Up Triggers Relay Board

[chrisrust]

I have a question about the relay board.  Whenever power is disconnected from the module and then reapplied the relay triggers.   I have a device connected to the relay board's common terminal and the normally open contact and I'm using a digital output pulse.  I also have the channel on the module setup to fail-safe digital output to off.   The relay turns on when power is first connected and stays on until I use a widget to control the relay.  Once I've done that everything works fine.  The fail safe is working fine whenever I disconnect or reconnect the ethernet cable.  Does anyone know what I am doing wrong or can do to prevent the relay from being activated when power is first established?  If I connect this to my garage door opener I do not want it to open the door if power is lost and re-established to the module while I am away.

[chrisrust]

Here is some additional information that I hope helps.. 

The relay is clicking on when power is applied.

The fail-safe for the digital output is set to Off

The digital output was not on when the power went off, I'm using a digital output pulse of one second.

The channel is in the I/O mode. 

The relay is wired to use the "C" and the "NO" connections on the same side. 

[jason]

The software failsafe can only do so much.  There is still a tiny window during start up that the all the pins default to inputs.  At that time, the on board pull-up resistors send the digital output pins high.  This wasn't a problem with the first version on the IO-204 because it didn't have pull-ups on it.  But the advantages of adding them outweighed the disadvantages of leaving them off.  Unfortunately, you've discovered one of the disadvantage of adding them.

But there is a work-around! 

All you need is a 1k resistor stuck in the pass-through connector of the relay board.  Place one end into DO and the other into GND. (see attached picture)  Set the failsafe to 'OFF'.

[chrisrust]

I tried the 1K resistor between DO and GND on the passthrough connector but the result was the same.  The relay still closes and remains closed until clicking on the widget following a power up of the module. 

Could you also clarify "Set the failsafe to 'OFF' ".  I wasn't sure if you meant the option "Fail-safe Digital Output to Off" or "Disable Fail-safe".  I tried both settings but the results were the same. 

Any other ideas?  I can't imagine that I screwed up putting in the 1K resistor between the DO and GND pins. 

[jason]

You are right, that is confusing.  I guess that is one consequence of calling the digital states on/off instead of 0/1 or low/high.

I tested it here and it worked how you are asking.  I also had another user try this method and it worked for him.  As long as the failsafe isn't set to "on" this should work.

- Relay board in channel 1
- Channel 1 digital output set to off (do this through the module settings page)
- Digital output pulse widget, Current State Pulse Type, 1000ms
- 1k resistor pins 3 (DO) and 4 (GND) of the relay connector

When I do this and power cycle it, the relay doesn't click at all.

I'm trying to think of ways you could go wrong.  Maybe your digital output is set to on instead of off?  Or maybe you are using on one of the other pulse widgets (negative pulse)?
It could also be that the resistor isn't making a good connection inside the socket.  I know my resistors get a nice layer of oxide on them when they have been sitting in my parts drawer for years.

[chrisrust]

Okay, the problem is solved!  I had the digital output set to ON instead of OFF.  I guess I don't understand what that setting does yet. Feel free to explain if you like.   

Now when I unplug the power to the module and then reconnect power the relay stays off.  I did notice however that it doesn't appear to make a difference whether the 1k resistor is connected between the DO and GND pins.  Could this be right? 

Thanks for the excellent support!

[jason]

For added insurance I would keep the resistor in there.  It still is possible to get a very fast pulse (a few milliseconds) on a power cycle.  That is the pulse I thought you were talking about.  Normally a garage door needs a pulse of at least a 1/2 second to actuate the door, but you never know!