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7 Optimized Solar Charging off grid for several output voltage potentials
Kanin Tangchartsiri
Lukas Gollings
WonJoon Lee
Akshatkumar Sanatbhai Sanghvi design_document3.pdf

Optimized Solar Charging off the grid for several output voltage potentials

**Team Members:**

Lukas Gollings (lwg2); WonJoon Lee (wonjoon2); Kanin Tangchartsiri (kanint2)


With technological advancements, our lives have tremendously changed and became more convenient. However, the environmental issues followed with the advanced tech and renewable energy sources remain as a topic of interest. There are lots of efforts to reduce carbon footprint ranging from installing solar panels to developing more efficient methodologies to save electricity. For people who cannot install solar panels, they may want alternative ways to use renewable energy without a need for the grid.


Our team proposes a solar panel integrated with a cascaded DC-DC Converter capable of providing multiple voltage outputs. We are looking to create charging capabilities for a multitude of different devices with different ratings (for e.g. AAA batteries, AA batteries, a smartphone) all within the same charging station. The overall product will look similar to a point of sale, whereby the stand itself is able to accommodate multiple devices (depending on the size and budget for our solar panel). Typical applications for this would include setting this device up to run in remote locations that are off the main grid which will allow the user to have access to a charging unit that’s portable for off-grid adventures like camping or hiking. The overall project is focused on displaying how much energy the users have saved.

**Design Specifics:**

DC-DC converters will be controlled using the duty cycle to replace (variable) resistors. In addition to this, for the accurate record of power savings, overall output energy used during the charging process will be monitored. For the most efficient power delivery, our design will have two DC-DC converters cascaded together, such that we can extract power efficiently from the solar panel and store this energy to be used when needed. The secondary DC-DC converter will regulate the intermediate voltage of the storage unit, and further provide galvanic isolation. We might need a 4 winding transformer, to provide galvanic isolation from the intermediate storage unit and the output batteries. This is a crucial step for the user's safety and also to ensure freedom of series connection at the output. In addition, this will be a good practice to reduce the common mode noise for the output reliability. We’ll also utilize MPPT algorithms to make sure that we have optimized our input power into the system and possibly as an extension project we can also have the unit track sunlight for maximum exposure.

**Solution Components:**

1. Input: Solar Panel Power Voltage Input (Solar Panels)
- Cost effective, efficient, and portable
- Commercially available solar panels on digikey are only rated at 1-2 [W], would need to create an array of solar panels to reach 10 [W] on output side

2. Synchronous Buck/Boost Converter

- Control schema to regulate the power being extracted from the solar panel
- Microprocessor creates duty cycle to regulate the intermediate voltage potential in the energy storage unit. The actual energy storage unit will be an off the counter mobile power bank to reduce complexity of a self designed battery.

3. Design of energy transfer process

- Need for appropriate voltage regulators to quantify the amount of power received from the solar panel
- Current Transducer (CT) and/or regular current sensors can be utilized to monitor that output and the calculations of power consumption will be done on our MCU.
- We can store our energy within a small scale power bank (over-the-self portable power bank) that should allow us to keep reserves of the energy.
- Stable intermediate voltage potential using a custom designed micro controller unit.

4. Secondary DC-DC Converter for several outputs

- Use of transformers to provide several different output potential voltages
- Analog USB power supply design

5. Output: Distribution of different voltage potentials for charging.

- Using the rechargeable batteries ordered, we will ensure the output potentials are restricted to the recommended current for charging.

**Criterion for Success:**

- Accurately display power output of the unit for users to see.
- Optimizes the efficiency of the solar panel unit to the maximum rate with our MCU.
- We aim to have an efficiency of 10% taking account of the losses in solar panels and other energy losses through some passive components. This number is relative to the input power from solar energy. If we’re talking about internally, we’re expecting an efficiency of approximately 80%.
- Able to charge differently rated devices, minimum of 3 different ratings (1.2 [V] at 700 mA (or 10% of mAh rating) , 2.4 [V] at a minimum of 1 [A] 5V at 2 [A] ). (standard AAA rechargeable battery)

**Current Competitors and Designs:**

- These don’t make use of optimized algorithms to maximize efficiency and overall power output. They also do not account for differences in loads and overall demand that’s been plugged onto the device.
- Users have experienced problems with the voltage regulator causing unstable charging speeds. We would aim to maintain constant charging speeds, while recording how much energy has been stored in the intermediate battery regulator throughout the devices’ lifetime.

Habit-Forming Toothbrush Stand

John Kim, Quinn Palanca, Rahul Vasanth

Habit-Forming Toothbrush Stand

Featured Project

I spoke with a TA that approved this idea during office hours today, and they said I should submit it as a project proposal.

# Habit-Forming Toothbrush Stand

Team Members:

- Rahul Vasanth (rvasant2)

- Quinn Andrew Palanca (qpalanc2)

- John Jung-Yoon Kim (johnjk5)

# Problem

There are few habits as impactful as good dental hygiene. Brushing teeth in the morning and night can significantly improve health outcomes. Many struggle with forming and maintaining this habit. Parents might have a difficult time getting children to brush in the morning and before sleep while homeless shelter staff, rehab facility staff, and really, anyone looking to develop and track this habit may want a non-intrusive, privacy-preserving method to develop and maintain the practice of brushing their teeth in the morning. Keeping track of this information and but not storing it permanently through a mobile application is something that does not exist on the market. A small nudge is needed to keep kids, teenagers, and adults of all ages aware and mindful about their brushing habits. Additionally, many tend to zone out while brushing their teeth because they are half asleep and have no idea how long they are brushing.

# Solution

Our solution is catered toward electric toothbrushes. Unlike specific toothbrush brands that come with mobile applications, our solution applies to all electric toothbrushes, preserves privacy, and reduces screen time. We will implement a habit-forming toothbrush stand with a microcontroller, sensors, and a simple LED display that houses the electric toothbrush. A band of sensors will be wrapped around the base of the toothbrush. Lifting the toothbrush from the stand, turning it on, and starting to brush displays a timer that counts seconds up to ten minutes. This solves the problem of brushing too quickly or losing track of time and brushing for too long. Additionally, the display will provide a scorecard for brushing, with 14 values coming from (morning, night) x (6daysago, 5daysago, . . . , today) for a "record" of one week and 14 possible instances of brushing. This will augment the user's awareness of any new trends, and potentially help parents, their children, and other use cases outlined above. We specifically store just one week of data as the goal is habit formation and not permanent storage of potentially sensitive health information in the cloud.

# Solution Components

## Subsystem 1 - Sensor Band

The sensor band will contain a Bluetooth/Wireless Accelerometer and Gyroscope, or Accelerometer, IR sensor (to determine height lifted above sink), Bluetooth/Wireless connection to the microcontroller. This will allow us to determine if the electric toothbrush has been turned on. We will experiment with the overall angle, but knowing whether the toothbrush is parallel to the ground, or is lifted at a certain height above the sink will provide additional validation. These outputs need to be communicated wirelessly to the habit-forming toothbrush stand.

Possibilities: and individual sensors which we are exploring on Digikey and PCB Piezotronics as well.

## Subsystem 2 - Toothbrush Base/Stand and Display

The toothbrush stand will have a pressure sensor to determine when the toothbrush is lifted from the stand (alternatively, we may also add on an IR sensor), a microcontroller with Bluetooth capability, and a control unit to process sensor outputs as well as an LED display which will be set based on the current state. Additionally, the stand will need an internal clock to distinguish between morning and evening and mark states accordingly. The majority of sensors are powered by 3.3V - 5V. If we use a battery, we may include an additional button to power on the display (or just have it turn on when the pressure sensor / IR sensor output confirms the toothbrush has been lifted, or have the device plug into an outlet.

# Criterion For Success

1. When the user lifts the toothbrush from the stan and it begins to vibrate (signaling the toothbrush is on), the brushing timer begins and is displayed.

2. After at least two minutes have passed and the toothbrush is set back on the stand, the display correctly marks the current day and period (morning or evening).

3. Track record over current and previous days and the overall weekly record is accurately maintained. At the start of a new day, the record is shifted appropriately.

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