How to build a simple 12V DC trigger detector for AV gear (photos included)

Currently the operation of my Home Theater is distinct and separate from my home automation system primarily because my Logitech RF remote is a purpose-built remote that meets with the wife-factor for ease-of-use across the myriad of AV components in my theater system. However AV gear typically includes one or more 12V DC triggers that are used to signal various devices to power up or down based upon the voltage - for example, my pre-amp’s first trigger signals the Monster Cable power conditioner to power it up and it in-turn powers up the amps each after a certain delay to avoid a sudden current draw on the circuit. A natural linkage between the Home Theater and Vera is a 12V DC sensor that can be attached to one of the triggers to signal the Vera that we have switched to Movie mode, etc. There are 3 12V DC triggers on my current pre-amp.

I had asked if anyone had done this in,9074.msg69538.html#msg69538 where tinkerdoctor suggested that I used a Z-Wave Door/Window sensor and an electromagnet attached to the 12V DC and recently Vera1234 asked about reading/listening to a 12V trigger in,10334.0.html. Using an electromagnet is a clever idea but I found a relatively inexpensive way to build a self-contained 12V DC trigger detector so I thought I would share the details for others in case there is a broader interest amongst this community (see attachment 1 for the finished product).

I did not know how to accomplish what I wanted to do but after a bit of research I decided I could build a 12V DC trigger using an Everspring SM103 Door/Window sensor and a 12V DC reed relay. There are many different types of reed relays but I settled on a Single-Pole, Single-Throw Normally-Closed reed relay. Most are normally open which would have worked but the sensor state would have been the inverse of the trigger state (i.e. the 12V DC trigger will open a normally closed reed relay which akin to the magnet moving away from the reed switch inside the door/window sensor) so I went with the normally closed even though the form-factor was less than ideal.

Anyone who can solder can build this simple detector because I am by no means an electrical engineer - I learned what I needed to know on the fly.


[ul][li]Everspring SM103 Door/Window Sensor $44[/li]
[li]RemTech PRMA1B12 reed Relay = $2[/li]
[li]Mini-din 8/3.5MM male cable = $3[/li]
[li]22 AWG holding wire - 24 AWG would be preferred but I only had 22 AWG on-hand[/li]
[li]1 regular staple[/li][/ul]


[ul][li]Philips screw driver[/li]
[li]Wire strippers[/li]
[li]Soldering iron[/li]
[li]Glue gun[/li][/ul]


The approach is to connect the normally-closed 12V DC reed relay dry contacts to the SM103 external contacts and the 12V DC trigger to the reed relay coil so that the trigger will open the normally-closed contacts simulating a door or window being opened allowing the Vera to sense the trigger state to activate various lighting scenes.


[ol][li]Pair the SM103 sensor with the Vera before modification[/li]
[li]Open SM103 and remove circuit board[/li]
[li]Bend and cut the regular staple to form a small clasp to hold the tamper-proof switch in the installed position (see attachment 1&2)[/li]
[li]Cut two 4" pieces of 22 AWG holder wire and strip both ends. These will be connected from the reed relay contacts to the SM103 external sensor connectors[/li]
[li]Solder the holding wire pieces to pins 1 and/or 14 and 7 and/or 8 respectively. I bent the pins together and soldered to both instead of simply cutting one of the unneeded pins off[/li]
[li]Drill a hole in the center of the lower SM103 housing on the end where the Z-Wave antenna is located and feed the mono cable through the hole[/li]
[li]Strip cut and strip the mono cable wire and solder the center pin (positive) to pin 2 and/or 13 and sleeve pin (negative) to pin 6[/li]
[li]Cut and remove pin opposite of pin 6 and adjacent to 8[/li]
[li]See attachment 4 for the reed relay soldered to the mono cable and the holding wires[/li]
[li]Cover the exposed bare contacts using a glue gun or electrical tape to avoid shorting the SM103 board or the batteries[/li]
[li]Cut the holding wire to length, strip and attach to the SM103 external contacts[/li]
[li]Tuck the holding wires into place and glue the reed relay to the battery post[/li]
[li]Replace the housing cover - I had to make a couple of notches in the housing cover for the holding wires[/li][/ol]

So that is all there is to it. This turned out to be a simple and pretty elegant solution for me and I encourage anyone who needs one and can solder to build one.


Very detailed, thanks for sharing!

Followed the steps to the letter and it works!!! Brilliant! So happy that I can control my other AV gear through this trigger! Thanks! :smiley:

Pleased to see that you successfully built a 12v trigger detector! :slight_smile:

  1. Keep the cool, nicely documented HW projects like this coming folks, and MCV may some day grant us a separate board to collect them…

That’s an interesting way to do things. I’m lucky that my preamp has a network interface so I can tell when it’s time to dim the lights for movie mode, etc. via EventGhost, but if you don’t, your solution would be really handy for some people.

Nice work. :slight_smile:

I use a Logitech Harmony (hub based) to control my home theater. When I use Spotify from my phone, it turns on the receiver but the Logitech hub isn’t aware. I’m trying to invoke an activity on the hub like “Listen to Spotify” so that other zones turn on. My thought was if I could sense the receiver turning on via the 12V trigger, I could have my SmartThings hub to invoke a Logitech activity. Will this solution work for that or does anyone have another solution? I like building stuff but also wondering if there any pre-built solutions available. Where are the photos? I’m brand new to the forum so sorry if the pics are here and I’m not seeing them. Appreciate any help.