Cf4ih17UAAApcR6

Prototype Version 5 Wins Gold at Regional Science Fair!

Following the end of the construction of the fifth prototype electric skateboard, I decided to enter my project into the Greater Vancouver Regional Science Fair. The experience was absolutely astonishing! Not only did I meet hard-working, dedicated students and their innovative projects, but I also met experts in the field of engineering, who offered creative criticism. And all of this couldn’t be possible without the committed judges and voulenteers, who took time out of their daily lives to set up and monitor this event. Way to go!

In order to make my project more scientific, I decided to run an experimental trial to see how the gear ratio effects the power consumption on the fourth prototype of the electric skateboard. I did this with several gear ratios and weights, and I used the results to improve the skateboard, by choosing the best gear ratio for my weight. I also determined the speed at which the skateboard has the maximum range, which turned out to be 19km at 9km/h. This is just an estimate; I still need to test that.

Bluetooth Logging System:

bluetoothlogger

I also decided to run an experimental trial on the maximum current and power consumption under different loads. Both of these trials were recorded with a custom-made, Bluetooth Logging Module that I designed, programmed and built. It uses a GPS to track location and velocity, a hall effect current sensor (for current), and the standard voltage divider/reference diode for voltage detection. More on the module in a further post.

Introducing Prototype Version 5:

IMG_3052

Prototype version 5 is the best, most complex prototype I have built so far. I had to learn how to work with carbon-fiber for this board, as I wanted to reduce the weight of the board even further. The deck has a foam-core, and I used wooden supports around the trucks. There were a couple of differences with the gear drive as well; I 3D printed two PLA spacers so that they could more easily hold the gear in place. Additionally, I used a 25 tooth gear that I modified. It used the least amount of power out of all the gear ratios tested.

The electronics side was a bit different as well. The largest change was the addition of a lithium-ion BMS board. I found one on eBay for about $15 for the 6 cell configuration I was using. The major advantage: safe and fast balance charging. I can charge from dead to full in under 60 minutes! I also picked up an inexpensive 24v power supply, which I modified to become a constant current/constant voltage source through the “33R Mod”. More on that in a later post.

IMG_3043

These were some of the major changes that I changed from the fourth prototype skateboard. Currently, I am working on alternative methods of controlling the board; everything from Wii-Nunchucks to Bluetooth Low Energy and Gamepad Controllers.

The development of this board, as well as the write-up and experiments that I did helped me win gold at the Greater Vancouver Regional Science Fair! I also recieved an award from the Canadian Institute of Energy, and I will be travelling to Montreal for the nationals in mid-May!

Read more

Weather Station: Designing the Circuit

IMG_0194

So now that most of the parts have arrived for my weather station, I have begun designing, testing, and programming the circuits for both the receiver and the transmitter part of the weather station.

So far I have connected the thermometer, barometer, and hygrometer sensors to the Atmega328P-PU chip on the breadboard. I have also connected the MX-FS-03V transmitter to the board and I still have 10 digital inputs left over.

On the top-left you can see an Arduino Uno which has the MX-05V receiver attached. I went through the sample code from the RC Switch and Virtual Wire libraries to figure out what was best for my setup. I eventually went with the Virtual Wire library and my own code. I found this website to be helpful in describing how to connect the modules.

One of the challenges I faced was parsing the code though to the send function which was included in the Virtual Wire library. I eventually found a solution using this code:

float p = getPressure();

char pbuf[7];
dtostrf(p, 7, 2, pbuf);

char msg[21];
sprintf(msg, “%s %s %s”, tbuf, hbuf, pbuf);

vw_send((uint8_t *)msg, strlen(msg));
vw_wait_tx();

This following code takes a float temperature reading, turns it into a char array, then combines it and 2 other readings into a single char array, which then gets passed onto Virtual Wire send. Shorter messages have a lower chance of getting interrupted or lost so I will stick with those in the final program.

IMG_0196

Another challenge I faced was providing the correct voltage to the 3.3v barometer. Since this is a minimalist breadboard design, the voltage actually comes from the 5v USB to Serial adapter; the BMP180 barometer will not work with 5v and it could get damaged.

I remembered that voltage dividers were a thing, so I incorporated one into the design. This is the circuit I used:

resistor3-3

Using a 100 ohm and a 200 ohm resistor (common values) in the circuit above will provide 3.3v to the barometer. Voltage dividers should only be used to power low amperage devices, and will not work with items like motors. It’s a “quick” solution to something that should be handled with a static voltage regulator.

In the image above there is a formula for figuring out the voltage of Vout, as well as the formula for the resistor power dissipation, which is 0.08 watts. 0.08 watts is not a big deal.

Now that everything was hooked up, I wrote a simple little loop which transmitted values across the room.

outputdraft

Easy so far! All I need to do now is hook up a voltage regulator, put all of the components onto a perfboard, and maybe even try some reed switch sensors! The code also needs a bit of work in order to extend the range, but that will come later.

Also, I started building the enclosure for the weather station out of some plywood:

IMG_0031

It looks like a bird-house!

While it’s not the best housing for taking accurate measurements, it should do the trick. In order to protect the wood, I plan to paint, then cover the entire thing with epoxy (or vice versa).

When I am done this project I will release all of the schematics/source files as well as publish some start-to-finish instructions on Instructables!

Read more

Plant Watering System: Building the Circuit

IMG_0116

What’s better than plants? Electronics and plants! Over the weekend, I designed and built a simple plant watering circuit using a couple of scavenged parts from an old wall charger.

IMG_0141

It works like this: if there is no water in the soil and there is water in the reservoir, run a pump which waters the plants. The motor would not run if there is no water to be pumped; a safety feature of sorts.

The circuit is very simple and uses only 1 NPN transistor, and only 1 PNP transistor. This is the first time I’ve designed something with transistors.

wateringsystemcircuit

Here’s a little gallery of the build/design process:

The next steps include connecting a proper water pump and putting everything onto a decorative base.

Read more