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At this point, we have a nice custom wall plate cut on a milling machine for the water softener salt-level monitor. Now it needs to be mounted in a suitable location.
Today, a fully-wired and automated home may include a command center of displays and controls for the thermostat, security system, CO2 detector, and fire alarm. The water softener brine tank sensor wires could be pulled through metal conduit to an approved electrical box beside the command center.
Unfortunately, my house was built in the early 1960s without consideration for the tomorrow-land of electrical devices. The basement is finished with a solid ceiling; which means it is difficult to pull new conduit horizontally to the proper wall. So, it would be a huge pain to mount the water softener monitor wall plate on the main floor.
Instead, I opted to place the wall plate in the basement outside of the water softener closet. It is in plain sight whenever I go downstairs to work in my machine shop.
The outline of the custom wall plate holes are traced with a pencil after lining up the plate with a spirit level.
Spirit levels are a combination of a straight edge and a transparent tube partially filled with a visible liquid. When the bubble in the tube is centered, the edge of the level is upright in relation to the Earth. By placing the level on the edge of the wall plate and lining up the bubble, you can make sure the wall plate is straight (plumb).
Of course, if your ceiling, floor, walls, and other straight edges are all crooked, the plumb wall plate will look out of whack. So, you may need to reference the nearest straight line to make the wall plate “appear” correct.
On the wall, trace the outline of the bar graph hole and the photocell hole with a pencil. Don’t trace or drill the wall plate screw holes yet, because the wall plate may need to shift depending on the quality of your cutting job.
Because this project uses less than 1 watt of peak power at a low voltage (5VDC) with a current-limited external power supply, I don’t feel it is necessary for it to be enclosed by an electrical outlet box. However, an electrical box is easier to service, is more rugged, and would be more professional.
The finished wall in my basement is ordinary drywall (gypsum board). Other than being a bit messy and chalky, the wall is easy to cut.
The space for the electronics is made by drilling out holes and then cutting away the pencil outline with a hacksaw blade.
I drilled out most of the outline with a 1/2 inch drill bit. For larger rectangular holes, I’d simply drill the corners.
A hacksaw blade cuts away and squares up the hole. A keyhole saw is a more appropriate tool, if you have one. For larger holes, a router with a drywall bit or a specialty rotary tool are good choices.
On the other side of the wall is the unfinished closet containing the water softener. I want to mount the printed circuit board here and have the bar graph LED and photosensor stick through to the wall plate.
Left: The motherboard is mounted to the wall after marking and drilling holes. Right: The cables are wrapped around a hook to prevent the board from being pulled off the wall.
The printed circuit board (PCB) contains four mounting holes for #4 screws. The screws go to the other side of the drywall and are secured with nuts underneath the wall plate. Since drywall isn’t very strong, it would be a good idea to add some washers.
To reduce the chance of ripping the circuit board off the drywall, the power and sensor cables are wrapped around a hook that is screwed into the wood stud. At some point, I’d like to make a suitable project box, but for now the motherboard is covered by a disposable storage container.
Although it works, this whole arrangement is amateurish and makes me question whether I should have just gone with a standard outlet box in the first place.
In any case, with the circuit board loosely mounted, I return to the other side of the wall to mark the wall plate screw holes. The spirit level is used again to ensure the wall plate is plumb. The wall plate screw holes are marked with a pencil and drilled.
Here’s a pretty cool trick that I discovered when I opened up an old Nighthawk CO2 alarm many years ago. If your display needs to be a little bit away from the PCB, simply add a bunch of DIP sockets to make up the difference!
Nylon nuts and extra DIP sockets space the display far enough through the wall.
Also, Nylon nuts were added to the screws to fine tune the spacing between the board and the face plate on the other side of the drywall. (You can see a bit of gypsum dust on the screws.)
The photoresistor is the last piece soldered to the motherboard, after the proper distance has been determined by the number of DIP sockets needed to match the wall board thickness.
Because the final distance between the main PCB and the wall plate was unknown until test fitting was completed, the photocell couldn’t be soldered until this point. Now that I’m sure the thickness of the drywall has been properly accounted for by the extra DIP sockets, the wall plate is pressed onto the LED bar graph part and the photocell is soldered to match that position.
Finally, what does the main circuit board look like?
