The Powers of Induction Log

Week of 1/22

This week we decided to change the direction of our project. Instead of creating optical character recognition software, we decided to instead build an wireless charger for mobile smart devices. We are planning on creating a stand for an iPad that allows the user to charge while watching videos or surfing the web.

Week of 1/29

We met on Tuesday, brushed up on some electrical engineering basics, and learned about the underlying principles behind inductive power transfer. We learned that iPads and iPhones do not contain receiver coils, but instead require an additional adapter to be able to receive power from an inductive charger. Many smart phones created by another companies such as Samsung do contain receiver coils. We decided to build a charging pad that will work with compatible smart phones. In addition, we decided to design and 3D print an iPhone case that contains an adapter so that audience members at the demo can try out the charger even if they have an iPhone.

Week of 2/5

Blake met with Andrew on Monday and researched Wireless Power transfer and the Qi standard for wireless charging. In addition, he watched a few tutorials on MultiSim, the circuit simulation software available in the ESE Teaching Lab. Elizabeth watched tutorials on AutoCAD and researched circuit design. In light of the feedback from our proposal last week, we are considering changing the priorities of our project and what our demo will look like. There may not be enough information for us to reliably design a charging station that will be compliant with the Qi adapter used by iPhones. We also need to specify our goals in more depth. What are the elements of our design that we really care about? It's likely that our current proposal lacks focus and sufficient detail. Instead of charging stranger's phones (which comes with the additional liability of damage), we are considering having our device charge something besides phones.

Week of 2/12

We met separately from Andrew to discuss the focus of our project and came to a better understanding of what we're trying to do. Our modified goal is to output charge to a wireless port instead of the more finicky Qi adapter. Elizabeth made a circuit diagram, and Blake worked on the design and refined the budget based on design changes. We both learned the functions of the various parts required for our design. We met with Andrew on Monday and explained our new focus then rewrote our Wiki page with our new information in mind. Our project seems more set in stone and realistic now that we have the details decided, and we are ready to order our parts as soon as it's approved.

Week of 2/20

On Monday, Blake continued trying to get a simple simulation to work on MultiSim. For some reason, the current and voltage coming out of the drain of the MOSFET was much lower than the supply side voltage. He varied the frequency of the pulsing gate source (which is standing in for the Arduino) to no avail. He fiddled with it and is now considering using an amplifier to increase the magnitude of the switching voltage on the drain side of the MOSFET. That way the magnitude of the voltage can be manipulated while the temporal frequency of the switching is preserved. Additionally, there are no bridge rectifier (although it was easy to construct a diode bridge with 4 diodes) or 7805 Voltage regulators easily available on MultiSim so it is difficult to test the validity of anything he's doing. In addition, he tried varying the coupling coefficient between the inductors to see if that made any impact. Perhaps he simply grounded something he shouldn't have. We communicated with Humberto (through email and a meeting) to discuss specifics of the circuit. He recommended we read a few chapters in The Art of Electronics, which we did. We met on Sunday to pull together some details for the evaluation on Monday. Elizabeth also modified the Gantt chart.

Week of 2/27

We all met with Humberto on Monday and discussed our project from a long-term perspective. Humberto pointed out that we still had to order our USB port, and we might need more coils and other backup parts in case something went wrong. So we compiled a list of parts we had, and ordered any missing parts, as well as some extras. Humberto also helped us consider what the motivation for our project is (since a wireless charger isn't a new concept) and how we would present this concept in a demo, so we began brainstorming about that. One idea we had was that the concept of our project (a portable wireless charger) could be used in a wireless-charging laptop bag. We also began considering the packaging of the project, but most of that will come later (though Elizabeth is starting to think about it from a SolidWorks standpoint). Elizabeth also designed a simplistic version of the Arduino switching code, and we messed around with an oscilloscope to start testing things.

Week of 3/6

Blake tried determining the inductance of the two coils with several different methods, each yielding nonsensical results. The methods employed include the following: measuring the time constant of a RL series circuit for which the value of R is known, changing the frequency for an RL series circuit until the voltage across the resistor is equal to the voltage across the inductor, and changing the frequency of an RLC series circuit until the entire voltage is across the resistor (finding the resonant frequency where the capacitor's complex impedance cancels with the inductors complex impedance. Any one of these methods should allow one to calculate the inductance with ease yet the disagreement in his solutions was disconcerting. He will try again with more meticulous care in the near future. In the meantime, he moved on to testing the transistor by making a small switching circuit with the Arduino. At a frequency of about 1 kHz (a total delay time of 1 ms), he was able to detect the square waveform across the load on the oscilloscope. Once an approximate inductance value is known for the transmitter coil he will try to (safely) connect the switching circuit to the inductor in parallel with a 1N4007 diode. This was a heavy exam week.

Week of 3/20

On Monday, Blake used the Arduino switching circuit (switching at 1kHz) to apply a pulsing voltage across the coil which was set in parallel with a diode. Instead of using the Li Ion battery as the DC power source, he simply used another Arduino pin set to HIGH (+5 V). The signal across the coil was convergent but highly irregular (as expected for the nonlinear diode element). He then tried moving another identical coil near the switching coil and measured the voltage across it. The signal's shape was preserved and at close distances the magnitude was almost equivalent. He then applied this varying voltage to a bridge rectifier circuit. The output DC voltage was about 2 V. Based on this result, Blake realized that either a higher applied voltage on the transmitter will need to be applied or by exploiting different inductance values on different coils or by both. If the 7.4 V Li ion battery does not supply enough power, a 12 V Li ion battery may be required. He's beginning to think about how to write an Arduino script for controlling the switching frequency. Blake tried to measure the coils' inductances again. He will figure it out this week. He doesn't know why this has been challenging. Over the last few weeks he has gotten much more familiar with oscilloscopes and function generators.