Pet Entertainment Bubble Tower With Laser Perimeter Sensing

Do you have a pet that is fascinated by bubbles. Our cat loves to watch our humidifiers bubble air up into their water tanks as water is slowly absorbed by the humidifiers' wicks. She has even knocked the tanks off of the humidifiers to apparently get at the bubbles.

I finally decided to make a purpose-built bubble tower just for her. I made the bubble tower so it had a perimeter laser beam that would turn on the air pump and an LED at the base of the tower when the beam was broken.

The bubble tower consists of:

1. Base (with controls)
2. Water Container
3. Light Source
4. Air Source
5. Automatic Control

This was a labor of love since our cat really had a thing for bubbles. Unfortunately she passed away before being able to fully enjoy it. We now have two young cats that are not quite as interested in the bubbles, but we'll see if they catch on. :-)

Here is the breakdown of the Pet Entertainment Bubble Tower:

1. BASE I wanted a large base to make sure the bubble tower was as sturdy and tip resistant as possible. I selected thin plywood as it is strong and should resist warping. The base has a raised control box to contain the controls and air pump and also to provide additional structure to keep the water container upright.

2.WATER CONTAINER Many types of containers were considered. I even thought of using a very tall glass vase, but I did not want to take any chances with our cat breaking it so I settled on plastic. I have used acrylic cylinders before (see Aquarium Table Lamp) but acrylic is fairly expensive. After hunting around on the internet I found a reasonable substitution, Clear Dust Collection Duct -- It's a thin wall PVC pipe. It is not as clear as acrylic, but it is about a forth of the cost. Being PVC I also knew that I could solvent bond the cylinder to a base of sheet PVC and not worry much about leaks.

3.LIGHT SOURCE I wanted the bubbles to be very visible as our cat was getting older and we think her eyesight may be declining. And if she wanted to watch bubbles in the dark I wanted to accommodate her. I decided to have an LED light source below the water container to shine up onto the bubbles as they rose up the water column.

4. AIR SOURCE The main criteria for the air pump was to have it very quiet. Not only did I not want to scare our cat, but I did not want it to disturb the rest of us as it turned on and off. After some internet searching I found a very inexpensive portable air pump that was exceedingly quiet. Being paranoid about leaks I decided there was no way I was going to have air come into the cylinder (a hole in a wall) anywhere below the waterline. So I constructed an air pipe that went up and over the top lip of the cylinder so there were no holes (almost none) in the water container.

5.AUTOMATIC CONTROL I did not want the bubble action to run continuously but to be automatic -- on cat demand. I considered several types of motion detection circuits, including PIR (Passive Infrared), Ultrasonic, Microwave ( there's a neat little circuit board out there) but all of these methods needed motion. The larger an object is and the faster it moves the more likely it is to be detected. Since the cat can lazily walk up to things I thought that a motion detector based on motion would not necessarily detect such "slow motion." I also wanted to continue to detect the cat if she decided to just 'camp out' and watch bubbles for as long as she wanted.

I decided that some type of beam break detection system would work well. I installed a laser beam system around the perimeter of the bubble tower base to that if she walked through it or laid down in it she would be detected and bubbles start.

1 - 18 inches of 2-1/2 inch diameter Clear PVC Dust Collection Pipe

1 - 2 ft x 2 ft x 1/4 inch thick Lauan Plywood

3 - 1-1/2 x 24 inch x 1/4 inch thick poplar boards

1 - 5 inch x 24 inch 1/4 inch thick poplar board

1 - Black PVC Sheet, Foamed or solid PVC 5mm thick (how it was sold), approx 4 inches square

1 - Clear Plastic Window, miscellaneous size big enough to cover the LED hole

2 - 36 inch x 3/16 inch diameter Rigid Tubing for Aquariums

2 - 90 degree plastic aquarium tubing elbows

PVC cement (like for PVC pipe)

Silicone Sealant

2-Part Epoxy Resin

1 - White 1 watt LED with star heatsink

1 - 5V USB Mini Aquarium Air Pump

1 - 5V Photo-resistor Relay Switch Module model XH-M131

1 - 1N4001 diode

1 - 10 foot length USB Cable

1 - USB wall Power Supply

4 - 8 x 8 x 8 mm Cube Neodymium (Rare Earth) Mini Magnets

1 - Inexpensive Red Laser Pointer

2 - 100 ohm 1/4 watt Resistors (in parallel; =50 ohms) for white LED

1 - Resistor for Laser Pointer (see text for value)

2 - 1-1/2 inch long pieces of large diameter drinking straw that your laser pointer and photocell will fit into

2 - Dental Mirrors

1 - Cap from discarded spray can for top cap of water tube (see text)

4 - #10 x 1 inch wood screws

Miscellaneous mounting screws

Lengths of Wood, 1 x 1 trade size (3/4"x3/4" actual) pine for mirror corners, box fasteners, water column support

1 - 1/4 inch thick by 1 inch square miscellaneous foam

Flat Black Spray Paint

Wood Stain

Satin Clear Coat Varnish

Heat shrink tubing

Wood Glue

Silicone aquarium tubing

A Pet that likes WATCHING BUBBLES - After all this is for them!

TOOLS:

2-1/2 inch diameter hole saw

Hot Glue Gun and Glue

Saw (band saw or other)

Soldering iron and solder

Tie-down strap (for clamping wood box)

Misc drill bits and drill motor

Dremel tool and wood carving cylinder bit

The base was made to occupy one end of the 2' x 2' piece of plywood. So naturally the long side was 2' long. The narrow side was 5", determined by enough room for the bubble tower and the photo control and pumps.

The base was constructed of 1-1/2" wide, 1/4" thick poplar that was glued together. I used a tie-down ratcheting strap to clamp it together. I used the plywood to help ensure it was square. I also cut the lid out of 1/4" poplar and drilled a 2-1/2" hole in the center for the bubble tower.

Glue the base to the plywood.

I needed a base to glue the PVC dust collection tube to and also to mount the tube assembly to the plywood base. I used PVC sheet so I could solvent weld the two PVC pieces together. Solvent welding makes the two materials one, so the likelihood of leaking approaches zero. I cut out a 4" square base from the PVC sheet, drilled mounting holes at the corners and then drilled a 1 inch diameter hole in the center for the LED to shine up through.

I cut the lens at the bottom of the water tower out of a piece of scrap of clear plastic I had. It was about 2 inches in diameter so it would cover the 1 inch hole in the black PVC base, but also small enough to fit inside the PVC bubble tower (PVC duct/tube). I am pretty paranoid about water leaks so I ran a bead of silicone sealant round the perimeter of the lens and ran a bead of hot glue between the silicone and the center, where the LED hole would be. I pressed the lens firmly in place and let the materials harden.

Next I solvent welded the PVC bubble tower tube to the PVC black base. I applied PVC cement to the bottom edge of the tube and centered it into position over the lens. I added additional PVC cement to the perimeter to ensure it welded completely. After the PVC cement had hardened/evaporated I ran a healthy bead of hot glue around the tube. Belts and suspenders where water leaks are concerned!

I wanted the base to look fairly nice so I masked around the control box and spray painted it flat black. I also spray painted the control box flat black. I stained the plywood a nice light walnut color and clear coated it with satin clear spray.

The USB powered air pump came with a rubber sleeve over it, which I removed because I didn't want it to keep motor heat in. I hot glued a piece of the 1-1/2" poplar to the plywood inside the control box to make a base for fastening the air pump. I put down some hot glue and used a 3/4 inch plastic conduit mounting strap to attach pump to the wood mounting base. I put a thin piece of foam between the pump motor and the mounting strap.

I know that many motors and coils will give off back EMF ( a voltage spike) when they turn off. The motor was controlled by relay contacts and not a solid state control so I was not concerned about the switching of the motor but I still wanted to make sure any back EMF did not go out to the LED or the electronic photo control circuit. So I added a 1N4001 clamping diode across the motor terminals. The diode is oriented so it is normally in the non-conducting state (reverse biased) with the cathode (stripe) connected to the positive motor terminal. Should the motor generate any back EMF during shut off, that voltage is opposite the normal motor polarity so the diode clamps it and shorts it out.

A long inverted U-shaped tube (goes over the side of the water bubble tower to take air to the bottom) is constructed from the rigid plastic aquarium tube. The joint at the top is make by connecting two 90 degree plastic aquarium tubing elbows together.

Again a piece of 1-1/2" wide poplar is hot glued down as a mounting base. I drilled a mounting hole in the LED star heat sink taking care to ensure that a mounding screw would not short across the LED solder pads. I used a screw to mount it in place on the wood base.

I connected lead wires and two 100 ohm resistors in parallel (to provide a 50 ohm current limiting resistor) in series with the LED and the 5V driving it.

This time I used 3/4" square stock hot glued to the plywood inside the control box as a mount for the water tube (bubble tower tube). The 3/4" thickness spaced it above the LED and allowed the LED to shine up through the bottom of the water tube and illuminate the bubbles.

I marked the holes in the black PVC base onto the 3/4" square stock and used screws to mount it in place.

I had a cheap battery powered laser pointer from the Dollar Store so I decided to modify it and not buy a new laser module. I measured the current to the laser diode and then calculated the dropping resistor that I would need to limit the current from 5V USB supply into the laser diode.

This calculation is fairly simple. Measure the current I(d) through the laser diode, measure the voltage across the laser diode while operating, V(d). The dropping resistor voltage V(r) used to calculate the limiting resistor is found by subtracting the voltage drop across the laser from the 5V USB supply: 5V - V(d) = V(r). Then ohms law (R=E/I) is used to calculate the resistance, R, needed: R=V(r) / I(d).

I took a couple of resistors and soldered them in series to get the value I needed for my specific laser pointer.

The laser pointer, and for that matter the photo cell at the receiving end, are mounted in sections of drinking straw mounted in holes drilled in the side of the control box. Again 1/4" poplar is used as a support base for the straws.

I took 3/4" square stock and cut notches out at 45 degree angles to make the mirror mounts. I painted the mounts flat black and epoxied them in place at the corners of the plywood. I cut the mirrors off of their metal handles and while the laser was operating hot glued the mirrors in place so that the laser beam would end up shining back into the receiving opening on the left side of the control box.

I used some fog to make the laser beam visible for the photo (the laser beam is normally invisible unless it contacts something).

The XH-M131 photo control module is only hooked up to 5VDC, to power it and also the load it controls, so ignore the references to 220Vac on the hook up diagram. The photocell is placed into the left most mounting straw and hot glued in place. With the laser operating, adjust the sensitivity and delay potentiometers to get the results you want.

I cut a notch in the 2-1/2" tube opening of the control box lid to allow for the rigid air tubing and test fit it to make sure it did not bind when slid up and down the water bubble tower.

I wanted the control box lid to be secure (cat proof), but easily removeable in case I needed to service anything. I decided to fasten it in place using magnets. I took 3/4" stock and hot glued a block near each of the 4 corners. I drilled pilot holes in each and screwed a #10 screw into each block. I then took the cube magnets and placed them on the screw heads. I adjusted the screws by screwing deeper or backing off until the magnets just sat proud of the lip of the control box. I then put epoxy glue on the top of each magnet and slid the cover down into place so that the bottom of the cover contacted the epoxy on the top of the cube magnets.

After the epoxy cured I removed the cover and screwed the screws down deeper until the magnets just contacted the screw heads. My cover was now held in place!

Carefully fill the water tower. The black plastic cap on top is from an empty hornet spray can and just happens to fit nicely over the PVC tube that makes up the water tower along with enough extra space to accommodate the rigid plastic aquarium tubing. Plug the USB power cable into a USB power supply, block the laser beam and make sure the light and air pump com on sending a multitude of illuminated bubbles up the tower to a cat's delight!

Enjoy!