LiPo Solar Tracking Charger

Hi, I’m Ethan and I am a rising senior at Mills High School. For my main intensive project, I decided to make the LiPo Solar Powered USB charger. I added these features to improve it: solar tracking, temperature sensing, and battery voltage/charge level display. I chose this project because I was interested in renewable energy and the charger is something I can use in the future.


Ethan Z.

Area of Interest

Computer Science


Mills High School


Incoming Senior


BlueStamp has been an amazing experience for me to learn more about the engineering world, since I’ve never done something like this in the past. I’ve learned a lot about the basics of coding, electrical connections, and the equipment that I used such as the soldering iron, the drill, and the glue gun. I’ve also met a lot of other students from other schools, and it was very exciting to quickly start talking to them and become friends. The staff also have been very helpful as they taught me how to be more independent and problem solve on my own. They also trained me on a lot of equipment needed to build this project and gave me very useful advice when I was building. During the first two weeks, I didn’t think I would be able to get through the six weeks due to how clueless I was. My project was overall very difficult and I hit a lot of walls when I was building. However, through consistent and productive research as well as perseverance, I was able to learn a lot and soon became able to create a successful and working product. Although I am still considering what I want to do when I get older, I’ve gotten deeper insight on potential future careers through BlueStamp.

Showcase Night


For modifications, I added a couple of new features to my solar powered USB charger. First, I implemented a solar tracking feature, so the panel will turn towards the direction with more light. To get this to work, the main components were the two photoresistors — light dependent resistors that decrease in resistance with increasing light intensity (photoconductivity) — a 55g servo, and the Arduino. I coded the Arduino to read the difference in light intensity between the two photoresistors. When more light is shining on one side, the Arduino will send data to the servo and the servo will automatically turn towards that side with more light.
Another feature that I added was temperature sensing. This was not as complicated and difficult as the other modifications. Essentially, I soldered in a thermistor — a temperature dependent resistor that decreases in resistance when heated — into the LiPo charger and taped the thermistor to the LiPo battery. Now, the LiPo charger is able to detect the battery temperature, so that when the battery gets too hot (50°C) or too cold (0°C), the charger will automatically stop charging. This will protect the charging system from breaking because hot batteries often indicate that something is wrong. 

Solar Tracking System

Solar Tracker, Sun Tracking, system, project, BlueStamp Engineering 2018
Here is how I designed my solar tracking system. I attached two wooden stands to the base and I attached the servo to one of the stands using zip ties. Then, to make the panel turn, I had to make it sit on something, so I used two wooden dowels and drilled a hole through the stands and attached a bolt. To create the stands and the dowels, I had to first get the material. After I got the plywood, I was able to create the base by measuring the proper dimensions and then cutting the wood using a handsaw. Then, to create the frame, I also had use a handsaw to cut the wood into the length and height that I wanted. After, to drill the holes, I had to learn how to use the drill and was properly trained by the staff. I learned that I had to find the correct drill bit so that it matches the measurements of the bolt I want to insert into the holes. Then, I used nuts and washers to secure the frame. By attaching Velcro to the wooden frame and the back of the solar panel, I was able to attach the solar panel into its proper position. All I had to do left was attach the servo horn to the solar panel somehow; this led me to think about using a paperclip since it is strong, durable, and somewhat flexible. I bent the paper clip into a hook shape and attached it under the Velcro of the solar panel. To secure it, I hot glued the top of the paperclip (not the hook) to the wooden frame. This was the hardest challenge for me so far, since the solar panel would either rotate really little or too much only on one side. To fix this, I used the serial monitor in the Arduino IDE to monitor the position of the servo horn since it can only rotate 170-180 degrees and has a minimum/maximum position. Additionally, I also utilized trial and error and kept repositioning the servo horn and the paperclip so that it would rotate the correct amount that I wanted it to. Finally, after many days of adjusting, I was able to create a successful, working, solar tracking system. 

Soldering in the Thermistor

thermistor, AdaFruit MCP73871, USB, DC , Solar Lithium Ion/Polymer Charger, Soldering

Servo Connections Schematic

servo, schematic, connections, solar tracker, arduino, BlueStamp Engineering 2018

My Final Milestone

My last milestone was to connect the Arduino to the charger and the LCD and code it to display the battery voltage. I connected the LiPo charger to the Arduino through the ground and A0 pins. Then I coded my Arduino to read the voltage through the A0 pin. To get my LCD to power on, I used an I2C adapter and connected the pins to the Arduino: GND to GND, VCC to 5V, SDA to SDA, and SCL to SCL. SDA is the data signal, which allows me to actually display the voltage from the code in the Arduino IDE. SCL is the clock signal, which ensures that the communication between the Arduino and the LCD is concise and reliable. To make the Arduino get sufficient power without my computer, I connected the boost converter chip to the Arduino, so GND to GND and 5V to Vin. For this milestone, I had a lot of challenges. First, I had trouble figuring out how to power the Arduino and how to connect the Arduino to the charger and the LCD. This required a lot of research. Another challenge that I had was definitely coding my LCD using Arduino to display the voltage of the battery. For my next milestone, I plan to make the LiPo solar charger sense temperature changes using a thermistor so that it will turn off the battery if it gets too hot. Then, I will make it sun tracking using photoresistors and a servo. Lastly, to make my project complete, I will make a case to fit everything and make my charger look nice. Making it this far was definitely challenging since I’ve never worked with these parts before. Before this, I had no experience with coding Arduino or coding in general. I learned a lot after working with Arduino and so far, it has been really fun to make.  

LCD and Charger Connections Schematic

solar, usb, charger, LCD, LiPo battery, Arduino, BlueStamp Engineering 2018, Adafruit, Buckboost


My First Milestone

For my first milestone, I assembled the LiPo solar powered USB charger by connecting five parts: the solar panel, the LiPo charger, the LiPo battery, the AdaFruit 5v USB BuckBoost, and my phone. I needed to know how to wire circuits and how to solder. To learn how to connect everything, I had to research a lot about the different functions and connections of each part. For example, I was unaware that the solar panel required a DC adapter cable, so I had to research what type of adapter it needed in order to connect the panel to the solar LiPo charger. Also, to connect to my phone (the load), I needed a USB port and a voltage converter so I bought the BuckBoost. After I knew I had all the parts, I soldered in all the parts, which was a very easy task. I didn’t really come across any challenges, but I did need to add more solder to the capacitor since it was getting loose and bent. Overall, I’m glad I was able to assemble a working charger and learn how the chips worked with solar energy with research and a little bit of thought. For my next milestone, I will be coding Arduino to monitor and display the output voltage of the battery through an LCD display or a serial monitor. This will be difficult and require a lot of learning since I don’t have any experience with C++.

Simple Connections for LiPo Charger

LiPo battery, BlueStamp Engineering 2018, Solar panel, Adafruit Buckboost, MCP73871, LiPo charger

Starter Project – MintyBoost

For my starter project, I decided to make the MintyBoost. The MintyBoost is a small, portable, USB phone charger which uses two AA batteries, each consisting of 1.5 volts. Coupled together, the total amount of voltage is 3 volts. This voltage goes through the printed circuit board, which consists of many different soldered components. First off, the resistors limit the flow of electrons in a circuit and there are data pins which recognize what is being charged. If resistance is too low, the MintyBoost will not work due to excessive current, according to Ohm’s Law. Next, the ceramic and electrolytic capacitors keep the voltage stable and precise in the boost converter chip. After the capacitors, the current flows into the power inductor, which is used by the boost converter chip to store and convert power from low to high. The boost converter chip converts the 3 volts from the AA batteries into 5 volts, which will make the current decrease to 0.5 amps. A major problem was only desoldering because I soldered in the wrong components into the wrong slots of the PCB. I also broke one of the resistors so instead of a 49.9K resistor, I used a 47K resistor as a replacement.

The Finished Product

MintyBoost v3.0, portable, charger, USB, AA, Mint case

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