Prototype Builds

Below are some pictures we created to give ourselves an idea of what our final product might look like at the beginning of the semester.

Charging Unit side view
Charging Unit top view

Base Unit side view

Base Unit top view

After we did our research, development and testing of each part of our system; we began to build each side of our system.

dock test setup

Above is our dock test setup for the initial build. It has a USB enumeration chip, PIC16 micro-controller, H-Bridge, and inductive coil with capacitors tuned for 100kHz. The PIC generates two PWM square waves at 100kHz to drive the full H-Bridge.

coil test circuit

Above is our portable test circuit. This is just the inductive coil with tuned capacitors, 4 diode rectifier, Step-Up/Step-Down converter, and a LED. When the coil is placed in the magnetic field produced by the dock coil a sine wave is picked up. The 4 diode rectifier changes the sine wave into DC voltage. Then that DC voltage goes into the Step-Up/Step-Down converter and is transformed into current. This current is then used to light up the LED.

Test circuit working

above is our system working and lighting up a LED, we used this to verify that the Dock was properly transmitting.

Our Induction System

After the Dock was verified as transmitting correctly, we interfaced it with the Portable both at the initial build. On the left hand side you can see our charging dock. The top left green color board is the H-Bridge.

On the right hand side you can see our portable. The top part of the portable is the LiPo battery. This LiPo battery powers the board and LCD until it reaches our programmed low battery voltage. If it reaches the low battery voltage the system will switch to low power mode and wait for the battery to be charged. This prevents the battery from entering a region where it will no longer charge. Below the battery is our board and LCD. The board changes the incoming sine wave into DC voltage by sending the signal through a 4 diode rectifier. Then we take that voltage and input it to a Step-Up/Step-Down converter that changes the DC voltage into current. We then send this current into our charging chip and a small amount is also needed to run the fuel gauging circuitry. The PIC18 monitors the current in and out of the battery along with the voltage. We also have the PIC18 programmed to compute state of charge (SOC) in percent and time left on the battery. The portable circuitry is powered by the battery, so during operation there is a loss in current from that inductively received and that actually sunk into the LiPo battery to charge, measured to be less than 10mA at extreme cases with the currently populated parts in our design. The micro-controller on the Portable, known as the Fuel Gauge Controller, gathers samples of the instantaneous battery voltage and current through the use of external ADC chips and computes the battery characteristics through coulomb counting techniques to display them on the LCD. The LCD is only enabled to display information by an interrupt that wakes the Fuel Gauge Controller through simultaneous activation of the proximity sensors no matter the state of the Portable whether it be mounted or not on the Dock. This was implemented to conserve power used by minimizing the LCD enabled time.

We completed the final build, below are our layouts. We followed the same procedure for the initial build.

Click here to view the final Dock layout

Click here to view the final Portable layout

The video below demonstrates the necessity for a protection circuit on LiPo batteries since they can explode when over-discharged, charged, or heated.