Category Archives: Projects

Craft, Hardware, or Software projects I’ve done

A List of Bubble Displays

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I’m going to be building a bubble display. So, here is my collection of related work:

  • The Information Percolator ( video ) – 32 tubes, 40mm in diameter. Overall display size 1.4m (wide) by 1.2m (tall). Approximately 25 separate “bubbles” can fit in a 1.2m tall tube. Water was used as the medium. 40mm tubes worked “better” than 20mm or 25mm tubes. Used an aquarium air-stone as the diffuser at the bottom of each tube. Each tube was also connected to all other tubes and a drain so that the water level would be equalized between them, and the water could be drained. Each tube was powered by an aquarium air pump controlled by a solid state relay. Each tube had it’s own check valve (to keep the water from flowing into the pump when turned off) and an airflow adjustment valve (to adjust for variations between different air pumps). Timing of air release is accurate to a few milliseconds, but only 25ms accuracy was needed. Note that the time a particular tube was “off” modifies how much water needs to be expelled from the system before air will flow, so sometimes 50ms is needed to produce a bubble.
  • Bubble Display (video) by Jon Bennett, Sahinaz Safari, and Gouting (Jane) Chang at the University of Waterloo is very well documented. It used glycerin as the medium and non-defused bubbles for a cleaner look and a slower scroll rate. 24 valves spaced 4.7 cm apart with baffles to keep the bubbles separated. They used a high pressure compressor with a regulator to output 12psi air at each valve. They had air pressure “accumulators” to provide a buffer so multiple valves firing at once wouldn’t reduce the pressure too much. They also had a manifold (possibly with valves to modify the air flow to each valve?) A check valve (clippard MCV-1AB) kept the glycerin from flowing back into the system. They eventually selected Parker A005-C23-2P valves that were operated for 10-20 miliseconds “on-times” (50 microsecond timing resolution was required). His suggestion was to use even smaller valves. Overall cost was large, due to the use of “full-price” pneumatic components.
  • The bubble Screen ( Video ) Bubble Screen by Beta Tank – The website was down when I accessed it, so not many details currently available.
  • Matt Bell has been working on a small bubble display and making steady progress improving it. His display uses solenoid operated valves to inject the bubbles, and his improved version uses individual tubes for each column.
  • Update: PipeDream III – I missed this one in my initial roundup, but it was mentioned in the comments of a hack-a-day post. Uses small tubing so that the bubbles don’t “catch up” to previous bubbles and solenoids to add the air.
  • Update: Bulb Bubble Display (video: video ) – I believe this bubble display was completed in 2013 (after mine) and I found it via a post to my bubble displays project video page on YouTube. It uses 64 tubes, with compressed air injection via valves controlled via shift registers. The tubes are part of a “garden partition” or tuftex type plastic wall that is already divided into cavities. I LOVE the idea of using that for the tubes, as it eliminates a lot of the tube construction / allignment issues (although I imagine you still have to seal the bottom well… They used silicon molded on the bottom of the “wall”).
  • If I missed your favorite bubble display, send me a URL linking to some useful information!

Not bubble displays, but related, waterfall displays like this one, this one, or this one are also cool, but run a lot faster, and in the opposite direction.

My thoughts:
Water for a fast rising bubble, glycerin for a slow rising bubble. Air-stones for a diffused look, or a tube for solid bubbles (which look better in glycerin)…overall the choices appear to be an aesthetic one.

Everybody who starts off with a single tank eventually goes to a series of tubes or baffles to keep the bubbles from interacting with each other (drag and drafting effects), unless they space the bubble generators out very far apart.

Carefully controlling the amount of air that is released appears to be the hardest aspect of the project. Aquarium pumps appear to have less control than solenoid operated pneumatic valves.

Common problems were leaks and difficulties sealing tank seams and mounting issues.

The biggest cost appears to be the hardware for each tube that produces the actual bubbles, with pneumatic (solenoid operated air valves) being more expensive than aquarium air pumps. I don’t plan on paying retail for my air pumps or electrically operated valves. Now, if only I could find a surplus supplier of check valves….

Most of these bubble displays were relatively short. Seeing as how you get the vertical axis “for free”, it seems like you should make your bubble display as high as your tank/tube allows. At a minimum, a six-foot height sounds like a good starting point.

Robot Pool Skimmer Propulsion Test

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One of my long term projects is to build a robot pool skimmer. It will probably turn out to look even more ghetto than this pool net taped to the front of an RC boat:
Radio Controlled boat with pool net taped to the front

The point of this exercise was to test the thrust of the motors on one of the boats I purchased as a donor hull. It is able to push a normal sized leaf net around the pool (slowly).
RC boat moving in pool
Continue reading →

Modifying LED christmas lights to run off of 120 volt DC

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christmas lights on the front of a truck.

Normal Christmas lights will run off of a 120 volt DC source just as well as an AC source because they are a resistive load.

LED Christmas lights will also run off of a 120 volt DC power supply (such as the traction pack on my electric pickup), but because they are diodes the polarity of the supply voltage must be correct. With the string I bought, half of the string was oriented one way, and the other half of the string was oriented the opposite way. This results in each LED only being lit 1/2 of the time when powered from an AC line, but if you plug the string of LED’s into a DC source only 1/2 of the string lights up. By reversing the connections at the middle of the string I was able to get the whole string to light up.

Of course, it could be that the LED Christmas tree lights are designed to only operate at a 50% duty cycle, so I may be over-heating them, but I figure that since they are mounted on the front of my truck they should get plenty of air cooling. So far they haven’t died!

Lensmount STL file for Opteka Fisheye Lens & Microvision show-wx laser projector

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Nirav Patel has made a 3D model of a lens/projector/globe mounting system for a Microvision show-WX laser projector, a Opteka fisheye lens, and a frosted glass globe for a spherical display system first described here using OpenSCAD. The OpenSCAD file is here. I went through the trouble of installing OpenSCAD and exporting the file as an STL file so that I could print it. If you want to avoid that trouble, you can download it from me here: lens_mount.zip.

Singer Sewing Machine Base gets a new table top

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Cast iron singer sewing machine base holding up a wood table top
My wife purchased a few singer foot petal operated sewing machine bases and we finally finished one of them. The table top is made out of a piece of 18″ x 36″ wood purchased from Lowes that I edged with a piece of rope trim. After lots of sanding to get the edges of the trim and the wood to line up (the trim started off just slightly wider), my wife took over and stained and sealed the table top. After I screwed it to the base she had cleaned up and spray pained, here is the finished result.

Using refrigerator door bins and vegetable crisper drawers for garage organization

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Garage shelves organized with cardboard boxes

Cardboard boxes are fine, but refrigerator door bins and vegetable crisper drawers are nicer for storing things. The good ones I used here are made from clear plastic so you can see inside them easily and they don’t block light.  

Garage shelves organized with door bins and vegtable crisper drawers from a fridge

Of course, they are terribly expensive to purchase for this use, but with the (lack of) quality of Kenmore /Amana refrigerators manufactured after 2004 you can find free donor components relatively frequently.   I also believe that with the addition of standard closet shelving support brackets the glass shelves from these fridges can be re-purposed into standard wall shelves.

Boost Converter Schematic

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Schematic showing a 2 phase boost controller with voltage and current sense
I have drawn up a schematic (click to enlarge) of the high current and sensing portions of my maximum power point tracking (MPPT) 2-phase boost converter battery charger circuit.  The schematic does not include the micro-controller, MOSFET gate driver IC, and associated power supplies, as those items are on the (relatively) low-power side of things.

What do all of these things do?

  • L1, Q1, and D1 – These three components make up the heart of the boost converter. When Q1 turns on, power builds up in L1 as the current rises. When Q1 turns off, all of that power exits via the only available route (out past D1) and the voltage is boosted as the inductor (L1) resists the current change. If you turn Q1 on and off very quickly (under control of the micro-controllers’ PWM output via a MOSFET gate driver) it raises the output voltage higher than the input voltage.

    • Continue reading →

The $25 Sous-Vide Egg cooker

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pid controller connected to an imersion heater in a bowl cooking an egg

I put together a $25 sous-vide egg cooker with a $20 PID temperature control module I purchased from ebay (which included a thermocouple and free shipping), a $2 immersion heater and a $1 extension cord (both purchased at a thrift store). I added a few crimp on connectors that I already had (but we’ll say you could get a few for $2 at the hardware store) and a free bowl and clothespin that I stole from the kitchen.

I’m happy to report that it cooked the egg just fine.

I’m not 100% certain I’m going to get into Sous-Vide cooking, but the technology has several alternative uses: unpasteurized milk heating for making cheese, automatic baby bottle warmer, etc…

A few downsides to my $25 setup:

  1. The temperature of the water in the bowl would vary by about 5 degrees from the top to the bottom as I did not have any type of pump to circulate the water. I was hoping that convection currents would do something for me, but apparently the water just stratified.
  2. It has a few exposed wires laying about, and a bowl of water sitting near them. For permanent use an enclosure will add to the overall cost.
  3. It can only cook a single egg at a time. The immersion heater draws 125 watts at 120 volts (around one amp) which can easily be switched by the internal relay in the PID controller (rated up to 3 Amps). But, it won’t work with anything big (like the electric kettle I also purchased at the thrift store) until I add a bigger 10-25 amp relay (solid state or otherwise). If you plan on running a big 8-12 amp load from your PID module, I suggest getting one that has a 12 volt output designed to directly control a solid state relay.

Adventures with a boost converter

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Breadboard with electronic components and wires, lighting up a lightbulb
A boost converter is a dynamic electronic circuit that can “boost” a lower voltage up to a higher voltage. Current is of course reduced in the process, but if you design it right you only lose 5-25% of the overall power. I am in the process of building one that will convert the approximately 70 volt nominal output provided by my solar panels into 125-140 volts that will charge my trucks batteries. I also plan on adding a bit of maximum power point tracking and battery charge regulation to the control logic, making it a MPPT solar boost converting charge controller. Why do I have all of these wires and parts scattered across the dining room table? Because the market does not sell what I need. (Believe me, I’ve looked.) So I have decided to build what I need.

Not being an electrical engineer, I probably won’t be able to get 95% efficiency out of my system, but so far I’ve measured 85-90% efficiency when doubling voltage. [Test 1: 23 volts in at 0.28A for 6.44 watts, 46 volts out at 0.12A for 5.52 watts means 0.92 watts loss = 0.92/6.44 = 0.142 or 14.2% losses. Test 2: 34.8 volts in at 0.35A for 12.18 watts, 72.3 volts out at 0.15A for 10.84 watts, or -1.335 watts loss, which is 10.9% losses.]

I’m still running things off of a (relatively) low voltage and current supply (two/three 12V 5AH batteries) while getting everything working, and only boosting up to 50-72 volts when testing.

I had the circuit up to 95 volts (max of 16 watts) on the output side, but I really want to optimize it for a voltage doubling, and you lose a good amount of efficiency when going higher than a 50% duty cycle.

I have also not been able to find a commercially available boost regulating control IC that works with 100 volt inputs and produces up to 200 volt outputs. One probably exists, but digikey doesn’t appear to have it. I’m solving this problem by programming my own using a PIC micro-controller. At least the programmable nature of my controller should also allow me to add the battery charging maximum voltage/current and solar panel MPPT logic into the system. I am currently working on a single phase boost converter, but the plan is for the final system to be two phase (which basically means that I use two of them in parallel). This means that I need my single phase system to be able to support 100-175 watts maximum. Soon I’ll be moving from my 25 watt resistive load (25 watt lightbulb) to a 100 watt resistive load. Eventually, I may even borrow a 75 volt power supply and test it up to 140 volts.

While working on my boost controller, I’ve found the following reference links very useful:

I have also made a few mistakes that people making their own boost converter may want to avoid:

  1. Within reason, the higher the switching frequency the better. I started off using a PIC12F683 chip which only has a single PWM output. Because I was planning on building a two phase system, I decided to code my own PWM loop that would support two phases with a 180 degrees difference. (A fancy way of saying that they would each be ON for the same amount of time, but that while channel A’s ON time would start at the beginning of the period, channel B’s on time would END at the end of the period. If the duty cycle went above 50% they would overlap for a bit in the middle.) After spending an hour on my fancy 2 phase PWM system and testing it with some visible LED’s, I took all of the delays out of it only to find that my 8Mhz internal oscillator could only support a period of 1.5-3 kHz. Sure, it sort of worked, but you could HEAR it switch. It also required a much larger inductor for the same power. So, I switched over to using the built in PWM subsystem, which can easily hit 73 kHz while still having 5-6 bits of precision. I now plan on switching over to a PIC 16F chip which has a dual channel PWM that I THINK can do an 180 degree 2 phase signal in hardware (if I’m reading the specs correctly…)
  2. Most MOSFETs require at least a 10 volt gate signal. If you switch them with a 5volt logic signal directly from the PIC they will switch (at least mine did), but they will not carry current without burning a lot of it up as heat. I was wasting 80% of my power as heat in the MOSFET until I wired up a transistor off of a 12V rail to amplify the signal to 12 volts. I plan on using a IXDN604PI gate driver chip for my final design.