Remote wifi temperature alarm

Son-off based Temperature/Humidity Alarm

I have systematically been adding automation and sensing to my home. I am particularly interested in finding and using low cost devices that interface with my wifi and I am focused on solving real home management problems while making life easier. If there is a little DIY involved in the solution then all the better.

The problem

I live in a place that gets pretty cold in the winter. If your heater becomes inoperative the results can be devastating. I travel so sometimes I am not home in the cold months of the year. Pipes bursting in an unattended home can be disastrous. 

I wanted to know if the temperature in my home drops to dangerous levels even if I was not there. Certainly a NEST or other brand home thermostat could solve this problem but they are costly. In addition I am not convinced that the savings from adaptive control really saves me the $$$ needed to offset the cost of the remote thermostat. Finally I also have an idea for a wifi controlled heater so I figured these were all reasons to build this wifi temperature & humidity control and alarm.

Wifi temperature/Humidity control

The heart of the alarm is the Sonoff TH16 Wifi Temperature and Humidity Sensor Switch. It allows you to monitor an environments temperature and humidity as well as to control when a relay turns on power to a locally connected device. 

The unit connects through your wifi to your phone where you can read temperature/humidity and define a set-point for EITHER temperature or humidity. It will not control both, its either or...darn!

The Solution

I decided to simply mount one of these units in an enclosure and plug it into a wall with an alarm connected to the outputs relay. That way when the temperature in the room dropped below a set point [I set mine at 40C] the relay would turn on an energize the alarm letting me know in the app and audibly that the temperature is to low in the home.

I use the eWelink app on my android to manage the controller

I found a nice alarm on Amazon that runs on 120vac. It is an easy form factor to mount and small in size while connecting directly to 120vac. I wish it was louder my wife does not!

The only thing left to do was mount it in an enclosure and find a way to plug it into the wall. I wanted to integrate the AC plug into the unit so that it plugged into and hung on the wall socket.

I found an electrical conduit fitting that was the right size, CARLON 1-in Pull Hub Schedule 40 PVC Compatible, Schedule 80 PVC Compatible, Conduit Fitting at Lowes [Item # 145137}. 

This junction box with modifications could house the sensor, plug and alarm. The TH16 would be mounted on the side of this conduit fitting. 

I also found a 3 prong plug that fit into the hole from the nipple sticking from the upper right of the conduit fitting. It is a Hubbell 15-Amp 125-Volt Black 3-Wire Grounding Plug [Item # 157821] which I also got at Lowes.

The build

I cut the right hand facing nipple from the conduit and after removing all but the plugs body it fit nicely into the remaining conduits hole. After wiring I glued the plug into the hole with plumber goop.

The TH16 was mounted with self tapping screws to the side of the conduit.

A hole 22mm hole was cut in the lid of the conduit for the alarm and a hole slightly larger than the plug for the sensor was also drilled into the lid in a position perpendicular to its socket. 

The sensor was mounted into the lower nipple and secured with a sheet metal screw. I had to cut a notch in the nipple so the shaft of the screwdriver reaches the screw.

The TH16 was wired through holes drilled through the conduit near the top of the TH16.

Universal Use

This build can be used to control any AC device based on either a temperature or a humidity range. 

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Here is a KIT to the Parts that are on Amazon