Power Inverter

I got this inverter a few years ago at Goodwill. The store had sorted it with the cups because it's shaped like a cup to fit in a car cupholder. This inverter is not great for electronics, but my pencil sharpener seems to be fine with it. I mostly use it with my solar power system. 

 

The spiky wave is from the inverter. The smooth sine wave is from the grid (both through a 120v to 3v AC to AC transformer.)

Kiwi Dragonfruit Soda and Jam

 Now that I'm in college, I'm addicted to Mountain Dew. I like to try all the new flavors. Then I started thinking about how I can make my own flavors of soda. My dad bought a used soda stream machine at a garage sale, and then I checked out a cookbook from the library, "Homemade Soda" by Andrew Schloss. 

The first recipe I tried is for kiwi syrup. I made a 1/4 recipe with 1 kiwi and added a few frozen dragon fruit chunks for color. I chopped the fruit into small pieces and then cooked it in a pot with sugar. Then I strained it into a container and added lime juice. The fruit pulp left over was coated in sugar syrup. I tasted it, and it reminded me of jam. For the second batch, I used 2 kiwis. I blended the kiwis and dragon fruit in my magic bullet. I thought this would make it easier to get a smooth syrup. Instead, it made a thick fruit pulp that would not go through the strainer very well, so more of it turned into jam.

From the Archives- Spin Art Machine

    The two spin art machines in the picture were a summer project in 2017. Griffin invited kids in the neighborhood to have fun and make some art with him.    

    Griffin has made many spin art machines in the past. He would start with an old motor, usually a large one. He has even used small motors like one from an electric toothbrush, or ones that came with electronics kits such as Snap Circuits (Amazon Affiliate link: https://amzn.to/3nnbYIy ) which already have experiments included for optical illusions with spinning circles.

    No matter what type of motor Griffin uses, he always makes sure that he applies the correct voltage for that type, so that it works well and doesn't get damaged. These spin art machines from 2017 were very basic, just a motor with alligator clips to connect to power. The motor shaft punches through the sheet of paper, and that can be enough to make the paper spin. 

    Markers work to make designs, but the patterns aren't very interesting. Paint makes great patterns, but is very messy! Griffin had the idea of putting the motor in a plastic bin to contain the splatter, but he didn't want to cut any holes in the bin. For this setup, he attached the motor to a heavy block of wood to anchor it, and then ran the wires out the top of the bin. The next step to prevent splatter was to add a lid with a target hole cut in the center. He made a lid from cardboard so he didn't have to cut a hole in the plastic lid that came with the bin, since this was temporary. 

    For smaller spin art machines with a tiny motor, Griffin would pre-cut the paper into circles. For larger setups with thinner paper, he would attach a cardboard circle to the motor shaft. He could use tape to attach it to the motor shaft more securely. It also supported the paper when it got wet and floppy from the paint. One time he tried a setup that could spin a two-foot circle. Unfortunately, it didn't spin very fast. 

Alarm Clock Repair

In college, it's important to wake up on time to make it to class. So my dad bought me a new battery-powered digital alarm clock. I liked this design because it uses a single AA battery which is easy to replace. Unfortunately, it was broken right out of the box. The one feature that is essential in an alarm clock- the alarm- did not work. My dad didn't want me to open it up to diagnose the problem because he thought he was going to return it or file a warranty claim instead. He procrastinated and did nothing, so after a year there was nothing stopping me from fixing it. I unscrewed the case and took a look at the circuit board. I used my electronics microscope to record what I saw. The problem with the sound was obvious. One of the pins on the piezo had no solder connecting it to the board. This was a quick fix. I resoldered it, and now it works.

Towel Repair and Decorations

 Although new fluffy towels are nice, the old ones are softer, dry faster, and take up less space in the wash. My favorite set that I have at college is the same set my dad took to college! It is starting to wear out, and needed some repairs and reinforcement.

I sewed white thread in zig zag stitch over a few holes. Then I couched over yarn in a wave pattern to keep the end of the towel from fraying. The triangle wave pattern was inspired by the standing wave reflection graphs from my engineering lab class.

Ice Dispenser Microswitch

Tonight my parents got home from a long drive after dropping me off at college. They were tired and thirsty so they went to the fridge to get a glass of ice water- but nothing came out of the water dispenser. So of course they called me for advice.

This is the same Samsung fridge that had issues with the water line freezing (see our repair video on Youtube about that fix: https://www.youtube.com/watch?v=whjh9TLSnSE), but it didn't sound like that was the problem this time. My dad did some troubleshooting and checked that the light inside the fridge turned off when the door closed and on when it opened. I told my parents to also check whether the light over the dispenser came on when they pressed a cup into the lever. Nothing came on, no lights or sound and no water or ice. But the light did come on when the light button was pressed. That meant it was probably a bad microswitch.

They looked up the model to find out how to unscrew and pry off the front panel. Then they took out the switch and called me back. I walked them through using a multimeter to test the switch. When the switch was pressed, it should have been letting more current through. It should have only measured 2 or 3 ohms, but it was measuring a resistance of several thousand ohms. So I told my dad to look for my drawer labeled "microswitches". He found one that was the same size and shape, just gray instead of black. The old switch was rated for 1A. The new one is rated for 16A, but it doesn't make a difference because this is a low current circuit.

My parents replaced the switch, and now the water and ice dispenser works again. I was able to help them fix it, even though I wasn't there. Maybe they should pay me for the part and a consulting fee.

Analyzing Flickering LED Christmas Lights

 Several years ago, when LEDs were just becoming popular, we bought a bunch of LED Christmas lights. They were OK but not as bright as the old style incandescent ones. They still had issues with bulbs coming loose so half a strand would go out. And of course the usual tangles. 

This year, after Christmas, I decided to buy a new set of LED lights to see if they would be any better. The new LED lights have more colors and are brighter, but seem to be more flickery than the old ones. My mom says that's not a problem- twinkling lights will look good on the tree. But it bothers me. So I decided to look at the wave patterns with my Lighting Analyzer and oscilloscope.

The wave pattern is not a sine wave or a half sine wave- it is pulsing. This explains why it looks flickery. To compare the frequency to 60 Hz, I added an antenna wire wrapped around the oscilloscope power cord (the purple line) because mains power is 60Hz. Next, I tested the old string of LED lights. It turns out that the old strand is exactly the same, just dimmer. So that's why we didn't notice the flicker on the old lights. 

Minty Mug Cakes

 I have been experimenting with microwave mug cake recipes. The best recipe so far includes colored sprinkles and vanilla for flavoring. I decided to try adding mint extract for a different flavor. We have plenty of mint growing in the garden, so I decided to take a recipe detour and make mint extract. 

One quick and easy recipe was for mint simple syrup, but this might mess up the amount of sugar in the cake. The other type of recipe was for mint extract with an alcohol base. The process is to chop mint, place it in a mason jar, add vodka, and let it sit for several weeks. The alcohol burns off during cooking, leaving just the mint flavor. This seemed like a good method, but I was impatient. I found another recipe to speed up the process. It said to cook the jar in a water bath at 135 F for 3 hours. My induction cooker wouldn't go that low, so I ended up cooking it for a shorter time at 140-160 F.  I will let it sit longer to see if it continues to get stronger before I filter out the mint leaves. Another option the recipes mention is adding a second batch of fresh mint leaves to add more flavor.

A year later, I made a new batch of mint extract, but used everclear as the alcohol base. It's 95% instead of 40%, so it seems to work better.

Back to the mug cake recipe. I started with a recipe by Lauren Allen from http://tastesbetterfromscratch.com/vanilla-mug-cake/ . I switched to oil instead of butter, and used more vanilla. I converted the 3 tablespoons of milk to 3 tablespoons of water plus one tablespoon of powdered milk. This way the dry ingredients (flour, sugar, baking powder, salt, powdered milk, and colored sprinkles) are shelf-stable, and then when I'm ready to cook it I add 2T oil, 2T water, and 1T imitation vanilla. After experimenting with different recipes and substitutions, this is the best mug cake I have found so far. The imitation vanilla flavor wasn't very strong, so that's why I wanted to try the mint extract instead. If I had store-bought peppermint oil, it would probably only take one tiny drop.   

Here's the final recipe with the mint extract:

1/4cup plus 1 1/2 teaspoons flour

2 Tablespoons sugar

1/8 teaspoon salt

1/4 teaspoon baking powder

1 Tablespoon powdered milk

1 teaspoon colored sprinkles

2 Tablespoons canola oil

3 Tablespoons water

1 teaspoon homemade mint extract

Mix and microwave for 90 seconds.

Light Flicker Analyzer

 After the problem I had with an LED sewing machine light flickering, I decided to build a lighting flicker analyzer. I built an adapter to connect a solar panel to my oscilloscope, which allows me to see a live display of the light level vs time.  

Light Flicker Analyzer

First, I tested the mostly dark room. It was noisy with no pattern. Next, I tested the old incandescent bulb. It had a mostly smooth pattern with a very low amplitude wave.

Incandescent bulb

Next, I tested the E12 LED sewing machine bulb. The difference was quite dramatic. It showed a pulse about every 9ms (60 Hz). This explains why my photos of the sewing machine had dark stripes- the light is flashing. It's barely visible to the human eye but obvious when I took a picture.

Flickering LED

Photo of flickering light

Finally, I tested the new LED bulb from IKEA. It isn't designed to go in sewing machines (too large to fit easily and almost too bright), so I tested it in an old candelabra light. The oscilloscope results look almost identical to the incandescent bulb. The wave is very smooth and barely noticeable on the graph. This means it probably has capacitors and a better control board.

IKEA LED bulb

Custom Screwdriver Handle

 

I needed to unscrew a metal plate on the old sewing machine to clean under it, but the handles of the regular screwdrivers were too long to fit. So I made a small wooden handle for a screwdriver bit. I used a hole saw with my drill press to cut a circle from a scrap of oak flooring. At the same time, it drilled the hole in the middle to be the right size for a very tight fit for the screwdriver bit. Then I sanded the edges and forced the bit into the hole.