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Multi-Purpose Node

It made sense to make a node that has a little bit of everything on it due to the fact that PCB boards are much cheaper to have manufactured when you order large quantities. With this in mind, I combined many features that I seem to use all over the house.

Right: Multi-Purpose Node with no temperature or  humidity sensors installed, two inputs missing, and no static protection.

Features of the Multi-Purpose Node:

  • Two 10 bit resolution analog inputs
  • On board LM34 Fahrenheit temperature sensor
  • On board HIH4010 relative humidity sensor
  • Optional probe (for running temperature and humidity sensors externally) with RJ45 connection
  • Four switch/sensor inputs for door sensors, buttons, or any other contact closure switch
  • Inputs have static discharge voltage protection
  • Two solid state relays capable of controlling up to 1A/60V each
  • Two motion detector inputs using Panasonic EKMC1601113 digital motion detectors (see below)
  • Power/Network status LED
  • Power supplied from RS485 network power distribution

The features are completely user selectable. So if I only need the two relays on the board, I can install them and none of the other features like motion detectors, analog inputs, etc. This keeps the cost down. Each of the nodes are configured using network commands to tell it what features are installed on it that are then saved to the on board flash memory in case of a power outage.

Where I'm using the Multi-Purpose Nodes currently:

  • Master Bathroom – Motion detector in the main vaulted ceiling, motion detector in the separate toilet room, humidity sensor probe for automatic exhaust fan control, and input from toilet room magnetic door sensor.  Also two thermistors attached to the hot water pipe going to the shower and tub for detecting when the shower is on and the tub is filling up connected to analog inputs 1 and 2 respectively.
  • Outside/Attic – Temperature and humidity sensors using the probe to the overhang of my roof, outside light level using analog input number 1 and a small probe to poke outside the overhang in my house.
  • Hot Tub – Water temperature using a thru-wall spa drywell (thermowell) and a thermistor connected to analog input 1, three waterproof IP65-rated SPST momentary contact buttons mounted next to the hot tub control panel that control lights inside, outdoor speaker volume, and station/track right from the hot tub using the inputs.
  • Wiring Closet – On-board temperature and humidity are monitored along with a fan pressure switch connected to input 1. More information here.

Motion Detectors

I still use motion detectors in several small rooms or large open rooms that need to be broken up into zones. For a long time I used the Insteon motion detectors, but these things are overly large and expensive. Not to mention mine ran through several 9V batteries a year which are a complete pain to change when they are high up. 

I came up with another idea to use Panasonic EKMC1601113 digital motion detectors. They are about $9 each and come in white, off-white, and black. There are two key benefits to using these. First, they are super sensitive and are true “occupancy sensors”, not burglary alarm motion sensors that you have to do jumping jacks to trigger. I can easily set it off with the slight wave of my hand while sitting in a chair. This particular model works up to 16ft away with a ~85 degree cone of detection. The second benefit (and most important to me) is the sensors size. It measures 0.4 inches wide in diameter and 0.5 inches long.

The only problem with them is mounting. They are meant to be used in a professionally designed PIR detector with PCB mounts. So I came up with a better solution. I wanted to use these overhead in my (vaulted) ceilings for vertical detection and on some of my walls for horizontal detection. To do this I would have to place them right in the drywall. The problem with this is you have no way to cover the rough edges of the hole in the drywall to make it aesthetically pleasing.

I looked around online for a solution and I ended up ordering 1/2” white hole plugs for $0.15 each that did the trick. The sensors are actually tapered from front to back, so it is slightly thicker at the base of the detector. Using a drill, I drilled a small hole in the back of the plug using the drill bit that fit the inside diameter of the plug. Once this was done, I slid the sensor into the back side of the hole plug and glued it into place. The further you push the sensor down into the plug (flush with the front) the wider the detection cone will be for sensing motion. If its completely flush with the front of the hole plug it will have it's maximum detection range. This come in handy for ceiling mounted sensors where you want to capture only motion in the room the sensor is mounted and not people's feet through the door in the next room.

Once the sensor was installed into the hole plug, you then need to solder the three wires (one for +5v power, one for ground, and one for signal) to the back of the sensor. I used some hot glue to cover the solder and pins when I was finished. After this, you can drill a 1/2” hole in the drywall where you want the sensor to be mounted and insert the plug. It looks great and at only a 1/2” diameter it's barely even noticeable in the wall or ceiling.


Sensor glued inside of the plug with a hole drilled through it.  Notice the hot glue on top to keep the conenctions from moving.

Final result that is ready to be palced into a 1/2" hole.


Jon Scott 2012 -- All Rights Reserved.