Monday, November 24, 2014

Addition of Digi-Pow Senior design project

I just wanted to make a quick post that I have added some initial information about my senior design project from my BSEE at the University of Florida. I did not do as great of a job documenting my project as I would have liked but I have layed the overall picture out on the Project Page on this blog. The goal of our project was to complete a prototype of a personal appliance wireless power meter that could transmit all data to a handheld device for viewing. I later added the functionality of being able to transmit to a cloud based application. It is my intention to lay everything out on the project page and then go into depth more about the design with blog posts later on when I have the time.

The project was a partnership with my friend and fellow student at the time Eric Iraheta. I thank him for all of his hard work and help with everything along the way. We decided on the coy name of Digi-Pow for our project; because of the digital based power meter design.

Final Prototypes
Sample cloud based application with live data

Monday, November 17, 2014

Putting together the motor driver

A picture story:

I have completed the building of my first motor driver board. This is a prototype so it has been constructed on a perf board protyping board that I bought at Fry's electronics. This is not meant to be a flying prototype just a test bed to get a BLDC motor spinning, and correctly controlled from the xMOS startKIT in a safe environment. Most of this will be explained by pictures and captions, because my last two posts were a bunch of text. The explanation of the component selection was done in this post, and the theory behind all of it was done in this post. Please read those at your leisure and interest.  

Testing the layout before begining soldering and jumpering.

First off I wanted to point out that this is the first time that I have used a perf board for prototyping. In the past I have always used a breadboard. This is largely due to the fact that any of my previous prototyped circuits did not involve as high of a current as the motor driver circuit will be drawing. I did not want to risk melting breadboard connections and blowing something up. So in short don't laugh at my first attempt at a perf board setup haha, but suggestions are welcome. I watched this short video in order to learn some standard techniques first and then gave it a shot myself.

Thursday, November 13, 2014

Bootstrap Gate Driver Calculations

Parts, datasheets, and Background:

As was mentioned in my previous post in order to successfully drive two N-Type MOSFETS in an H-Bridge configuration from a microcontroller a Gate Driver is needed to complete the task. The gate driver IC that I selected is a Fairchild Semiconductor FAN7842 High and Low side gate driver.

Gate Driver IC on breakout board for testing (quite small)
As you can see the IC is pretty small overall and is a relatively simple IC. It takes inputs from a microcontroller and translates that high or low value to the gate of the FET it is driving. The high and low signals are taken in separately and can be controlled separately. This gives the user programming the microcontroller more control however there could be an accidental BOOM! if the high and low sides are on at the same time. This means the programmer needs to be diligent in their work. Pressure is on haha.

Thursday, November 6, 2014

BLDC motor and controller theory

What is a motor controller? Why do we need it? What circuit topologies are commonly used? These are all good questions and I will try to provide a little bit of background from my limited knowledge on the subject.

DC Motors:

Let us start with the Motor. DC motors rely on the fact that current running through loops of wires produce magnetic field. That generated magnetic field in turn then produces a torque on a magnet (permanent or electromagnetic) causing it to turn. The wires are wound in such a way, and current supplied in the right order that the motor continues to spin round and round. This process is called commutation.

Brushed DC Motor:

 A brushed DC motor is called as such because the commutation process (the correct order of applying DC current to cause rotation) is typically done through carbon brushes pressed up against the commutator pads on the rotor of the motor. The current is supplied by a constant DC source. This process is also called internal commutation. While this process is initially inexpensive, reliable, and relatively simple, the brushes wear out over time and cause maintenance and repair down the road. Controlling speed is as simple as varying the voltage of the constant supply connected to the brushes and in turn increasing current. Below is an example of a basic brushed DC motor.

Wednesday, November 5, 2014

New Oscilloscope! Every engineers dream!

The Why...

For a long time now I have wanted to have my very own oscilloscope. Not just one that I could have access to but one that I could call my own and use on my bench, and use for my stuff. I feel like this is a want of every engineer's at some point,  or at the very least for those in the electrical field. Well I finally cracked down and bought one. The main reason why I could justify it was because I am in the middle of building a BLDC motor controller for my Gator Quad project, and a oscilloscope will be very useful for verification and tuning timings. Other than that, because who doesn't want their own... am I right?!?

I wanted a scope that was digital for two main reasons. The first being that digital scopes come in more compact physical platforms and I don't have that much space and move a lot so I did not want to be lugging it around. Secondly, I wanted to be able to connect my computer and pull wave-forms off of the scope directly, and not do the in between with the flash-drive. Obviously after that, I wanted as many features for as little as possible because I already feel guilty for not trying to salvage an analog scope so I might as well go all out. 2-channels is okay with me... I am sure that there are projects where 4 would be useful but I am sure I can get by on 2 for now. That's the other thing. I am a hobbyist, and will be using this for my own personal projects, I do not need to spend thousands of dollars to capture the waveform when I inevitably blow something up. So for these reasons I selected the following scope.

The What...

The scope that I landed on was a brand I was not too familiar with and was sold on amazon. It ran for $279 when I bought it. More than a lot of people would spend, but I felt it was reasonable for the amount of features I was getting and the reviews it had gotten on Amazon. Way cheaper than a "comparable" Tektronix scope or Rigol. Probably not as high quality but hey... Im just doing this for fun so... Yolo. On the upside I was able to buy it with bitcoin thanks to the services of GYFT allowing me to buy an amazon gift card with bitcoin. It worked quite well as a matter of fact and did not take much time at all to purchase an amazon gift card of $300 dollars from them that I was able to use immediately.

Siligent SDS1052DL 7" TFT- LCD Oscilloscope