Installing the Solid State Relay

I conducted a simple test today by hooking up the Solid State Relay (SSR) to the toaster oven and an Arduino's power supply.

The hot wire was already connected to both heating elements so I just connected the neutral side of the heaters to terminal 1 of the SSR using a connector I bought from RadioShack. Terminal 2 is connected to neutral in the power outlet. Terminal 3 and 4 are simply connected to 5V and GND on my Arduino. Having 5V across terminals 3 and 4 turns on the relay, creating a return path for current to pass through the heating elements. You can see that the toaster was successfully turned on.

Now, all I have to do is install the thermocouple and digitally control the temperature using the Arduino.

Taking Apart the Toaster Oven

Today I spent some time taking apart the toaster oven that'll be modified into a reflow oven. Not surprisingly, it was mostly empty. The wires seen here are temperature resistant, so I will be hanging onto these, and unlike most others I plan to keep the knobs in place for aesthetics. Now I need to figure out where to mount the thermocouple, which by the way I had to remove the heat shrink from because it will be heated beyond its 250C rating. I also now need to order the Solid State Relay I've been putting off buying.

Making a Reflow Oven

I've started working on a DIY reflow oven based on this instructable.

Instead of working on it my usual way from scratch I decided to do it the easiest and fastest way using an arduino and a breakout board from adafruit linked here.

Today I got my breakout board and thermocouple in the mail so I put it together and tested it with the example code provided on the website. It turns out that as people have noticed the thermocouples have incorrectly colored wires. This was easily fixed by reversing the wires.

I broke down the project into the following steps, of which I am now moving on to step 2. However, before moving on to the next step I will need to figure out if the heat shrink around the sensor can handle high temperatures. When I tested it over a lighter it was smoking a bit and most pictures don't show a heat shrink tube around it.

1. Setup and test the thermocouple
2. Install thermocouple in toaster oven and monitor its temperature
3. Order then install a solid state relay to control the temperature

Android App Tutorial

Just built my first android app following android's official tutorial. I've been pretty frustrated by the lack of Kindle apps so I decided I will build them myself. Specifically, I am frustrated most by Bloomberg's android smartphone and kindle fire apps. They are awful..

The tutorial itself felt kind of lacking. Given the ridiculous amount of app developers out there I'd assumed that the tutorial would be much easier to follow, but it does require programming experience. In fact it requires experience learning a new programming language or API. I'm no expert in either, but I guess I knew enough to get through the first step of the tutorial. Here are some interesting takeaways from my first step:

1. All 'Activity's must be declared in the manifest
2. Every 'Activity' is invoked by an 'Intent'
3. 'Activity's can get its invoker using getIntent()
4. Most programming is done within the framework provided. My job as an app builder is to work on the actual content

I'm not sure how long this will last, but hopefully my efforts will be fruitful.

The Trap of Design vs Analysis

"Don't be intimidated and just start somewhere"

Over my years as an undergrad, school exposed me to much theory and many closed form solutions. I have been inspired by the science and mathematics behind engineering. Having started from DIY high school I always found theories to be irrelevant for the most part, simply because any circuit can be tweaked to operate correctly. However, despite my initial preference towards practical learning, I somehow became obsessed with closed form solutions: solutions that can be entirely and certainly solved through theory and math. I couldn't step up to the task in my earlier graduate courses in analog IC design. In thinking too deeply about everything that could go wrong I forgot that what matters is that your design works.

A few days ago at my design review meeting with my professor about my LNA my professor clearly saw I was struggling. Even with the deadline approaching I was still characterizing the IC process to derive constants of the transistor devices. He then told me to stop being intimidated and start somewhere. I always found this prof to be very intimidating for how he speaks, but this time his words resonated (no pun intended) with me. He began sketching up a design based on the project specifications and very simple device parameters; before I knew it, he was done with enough to begin simulation.  

Although his design was using idealized components (no noise, loss-less, etc.) with all of the theory I've learned I can easily make up for the discrepancies later. Back when I didn't understand anything and I didn't know better but to build first, then learn, then fix. It turns out that I was doing the right thing all along! The only difference that knowledge of theory seems to make is in early design stages and when the bugs arise; with each bug we are simply able to make informed and goal-directed decisions. What's great is that this type of work can also lead to invention and innovation, as the frontier or engineering may simply seem like another bug. Theory moves engineering forward but only through implementation!

After telling my classmates the same thing all along, it's ironic that I would be trapped by the same mistakes of thinking I'm a scientist when I'm an engineer. I could never understand why people couldn't build, but now I understand why. I will forever appreciate my professor for saying that right thing at the right time. 

Realization

I've slowly come to realize how naive I am as a circuit designer. While working on my robotics circuits I have experienced unreliable circuit performance countless times. However, I had never considered to mitigate this effect through better design practices; instead I have constantly relied on programmed software calibrations to counteract variations between circuits. Considering that I use very basic 8-bit microcontrollers in my robotics projects, the several instructions for software calibrating sensor data was wasted processing time. Additionally, as someone studying circuit design this is a depressing state of ability to be in after studying so hard. Looking back to all of my circuits, I see that although my ability to analyze complex transistor typologies have grown I have never applied any of my new found skills. From now on I hope to utilize what I spent the last 4 years as an undergraduate studying as I rebuild old circuits and design new ones.

Optical Encoder Tested

I tested the completed speed sensor. The first picture below is the output waveform (sinusoidal-looking yellow line) of the photo-transistor. It looks like there are two traces because the infrared LED is pulsed. The straight top yellow line is when the infrared LED is off. The peaks of the output occur when the photo-transistor sees the least infrared light (reflected off the dark part of the encoder wheel) and the troughs occur when the photo-transistor sees the white sector of the encoder wheel. 

The two screen captures below show the output of the photo-transistor and comparator circuit. The comparator circuit compares the output to the photo-transistor with a reference voltage of 4V (mid-way between the peak and trough) and outputs 0V or 5V depending on whether the sensor output is bigger or smaller than 4V. The periodic glitches seen in the circuit is from the H-bridge, which is driving the motor with a 25% duty-cycle square wave. For the final mobot we will use separate power sources for the motor and the rest of the mobot.