Thursday, March 16, 2017

Off the Clock Design Kickoff: Books, Catalogs, Kit Specs, and Project Outline

Hello everyone! Last week I was selected to participate in Wurth Electronic(WE) Midcom's Off the Clock Design Challenge which is a 12-week design contest involving constructing a product around a 15W wireless inductive charging kit. I will be posting throughout the duration of this contest to make updates on my project status while also discussing technologies that I use at various levels, including principles of operation, design approach, and societal impact.

The contest officially kicked off for me on Monday morning when I received a package from WE that was quite a bit larger and than expected. Here's what I got:

Wurth Electronik sent me all of their design resources! I had enough time to skim through them all, so here's a quick firm impressions evaluation of each one. 

ABC of Power Modules: I don't work with power modules very often so I can't see an immediate use for this book. It provides a very high level overview of power converters and controls, and some more specific details on power modules including testing, module construction, and storage. 
ABC of Capacitors: I'm not sure how I'd really use this book, as it discusses basic principles of caps, characterizations, and capacitor types. Most of the material in here is easily accessible online. 
Trilogy of Magnetics: It's a big book with a wide range of information, but is too broad to be helpful if you're doing low-level magnetics design. Could be a handy reference. 
Trilogy of Connectors: This is probably the most interesting one! Something I didn't know in school was that a lot of my time working would revolve around connectors. I might take the time to read through most of this when I have the chance.
The LTSpice IV Simulator: LTSpice is the most widely used circuit simulator, but it's capable of more that what most people use it for. This is a very detailed (730 pages!) and thorough reference for all it's features and I'm sure it will come in handy at some point. 


The catalogs I received are over 2000 pages of parts! I've used Wurth inductors and transformers before, but was not aware of just how broad the portfolio was. 

The Kit

Here's the wireless charging kit in the box and in action! The kit consists of three circuit assemblies:
- TX unit supplied by 19VDC from AC mains.Transmits through inductor with diameter ~1.5 inches 
- RX unit that receives power and outputs 10VDC. The inductor has similar diameter, and the unit is supposedly capable of outputting 15W.
- LED driver that mounts onto the RX unit and lights up when powered.

Two initial observations:

- By taking the dimensions of the acrylic (2'x2'x.5') on the RX unit and using the acrylic density (1.18g/cm^3), the weight of the unit is estimated ~38 grams. I'll round this up to 45g as a conservative estimate to include the weight of the inductor. 
- By moving the RX+LED unit over the base and observing where the lights remained off, it looks like the RX unit can be moved +/- 0.25 inches from center in the X, Y, and Z direction while still powering the LED array. More on this later.

So my project proposal is to use RX unit as a charger for a drone. The unit will be mounted to the drone such that the drone can take off and land on the pad, charge, and then take off again without any human assistance. Quadcopters were popular quite a while ago but I know very little about them so this will also be new for me!
Primary Objectives:
- Make a battery charger PCB that is functional on the first fab attempt.
- Use as many Wurth components in the PCB construction as possible. 
- Have fun with the process and learn more about magnetics and wireless charging!
Secondary Goals:
- Add functionality to the shield to monitor charging status (currents, voltages), and log them via arduino. 
- Advanced battery management representative of good quality battery products.
- More functionality and customization so kit may be multipurposed for other applications.

OK, that's all for now, next week I'll be talking about selecting a quadcopter.

1 comment:

  1. Awesome idea! If you haven't yet, check out They have a great selection of DIY quadcoptor/drone parts, are fast to ship, and have good prices. Can't wait to see how this goes!