In wall power supply/transformer

I'm putting a bunch of sensors in places that I don't want people to mess with the power supplies. I'm thinking it would be nice to go from the typical 12/2 or 14/2 110v US mains wires to either 5vdc or 7-12vdc to power my arduino inside either a 2 gang old work box or 2 single gang boxes.

So, basically I'd like to know how other people handle this without the typical "wall wart."

Is there a good, inexpensive way to get a tiny power supply that could sit inside the box?

If I was designing this project, I would use wiring like the land-line telephones use and stay completely away from AC power. A single power supply could supply power to all your sensors and also provide a communication means back to a central site. Normal phone wire is 3 pairs of twisted #26 or #24 solid wire.

Paul

I'm starting to see USB ports in regular wall outlets. They look like they are significantly more expensive than a wall-wart but much more tamper-proof.

There's two downsides:

  1. The USB ports are more easily damaged than regular wall outlets if someone trips over the cord or bashes the plug with the back of a chair.
  2. People will unplug your devices to charge their phones.

Without having the whole thing enclosed inside the wall, it's difficult to keep it safe. A future electrician may accidentally put mains power onto your wires and then you have unregulated AC on wires with only 5V worth of insulation. That's why it is rare to see low-voltage wires coming out of a wall socket and when you do see it, it looks like the worst kind of hack job.

I do like Paul's suggestion: use phone jacks. They are built for wall mounting and are easily replaced if they get smashed. Be aware that someone may find a real phone outlet (or Ethernet) to plug your device into, so you've got to expect 48V AC as a likely fault condition that your device must withstand without bursting into flame.

Yep. Both of you are exactly right. That’s why I was trying to have the whole power supply behind a blank outlet cover. That would make it accessible but tamper-resistant.

I really like the idea of something like this 110v (or 220v) to 5v, I just wish it had screw terminals so I didn’t have to solder pig tails to it or put each one on a board.

Sorry. Forgot the link...

Have you explored a battery option with sensors run on deep sleep routines?

Otherwise for running power, I use 2 or 4 conductor security wire. It's in-wall rated.

I haven't thought batteries, primarily because this will go in 100 buildings on our campus and smoke detectors are enough of a challenge, but that is a good thought.

Yep...I think I'm going the central power supply with security wire method. Thanks!

mudmin:
I haven't thought batteries, primarily because this will go in 100 buildings on our campus and smoke detectors are enough of a challenge, but that is a good thought.

Yep...I think I'm going the central power supply with security wire method. Thanks!

Years ago we built circuit boards for a customer. They were temperature and humidity sensors that communicated using a mesh network to a central PC. They were powered by 1 or 2 D cells and placed in a PVC tube in walls under windows and covered with a blank outlet cover. They were designed to operate at least a year before replacing the batteries.

They were placed under each window in a multiple story apartment building.

Paul

Sorry. I know this is late, but thank you for that. I'm going to try that. I have 100 buildings to play with, so I can try lots of things.