Saturday, March 31, 2012

[6.002x] First lab session

Dear all,

In our weekly lab sessions, we will go through exercises that are designed to:
  • Reinforce 6.002x concepts, and
  • Show the practical usefulness of circuits.
I have attached the first lab worksheet which we will use in the coming week. Please take a look at it beforehand, and bring a printed copy to your lab session.

See you soon,

[Link: Lab worksheet]

* * *

After each session:

Friday, March 30, 2012

Setting up

Organized almost everything. Not enough energy to sort the pile of capacitors by the monitor...

(Microphone, accelerometer, thermometer, proximity, photocell)

[6.002x] Lab groups

Dear all,

For the lab sessions (starting next week), please form teams of 3 students (not 2 unfortunately). Each will meet with me for ~1 hour each week, where we will build, measure and analyze circuits.

Please decide on your team by the end of Saturday. Send emails to both me and Enky. (Only one email per team is needed.)


Thursday, March 29, 2012


Few days delayed (arrived on Tuesday night), after getting Internet access in Ulaanbaatar!

Leaving Stanford, with three boxes of electronics:

At SFO. The plane that will take me to Asia:

Twenty-four hours later (no sleep!):

And, after six hours of sleep:

Saturday, March 17, 2012

Skype lessons this week

Hello all,

This week I will cover on Skype:
  • Wednesday: Lecture sequence S5 ("Inside the gate")
  • Friday: Lecture sequence S6 ("Circuits with nonlinear elements")
See you in a few days!

Friday, March 16, 2012

240Vac "Stress test"

It occurred to me that I have to be incredibly careful with regards to 120/240AC power sources. While I am coming with lots of battery packs, solar panels, USB-powered sources -- these are all single-side DC sources. For the later experiments in 6.002x, such as those that deal with the use of opamps, we need to provide +/-15V supplies which cannot be as conveniently generated from "portable" power sources.

Additionally, it struck me that if any of the fuses blow, or the measurement apparatus is somehow incompatible with 240Vac, then this project can be held back. So, getting the things powered up correctly in Mongolia is a potential Achilles' heel.

For that reason, I'm going to "stress test" the instruments while I am still in the US, so that I can run down to a local Fry's store to buy replacement parts if things were to go wrong.

To begin, I got a 120/240 up/down transformer that I can use right now to simulate 240Vac (and also use to generate 120Vac in Mongolia):

First up is the oscilloscope. Check:

Next up is the function generator. Here, I exchanged the fuses according to the manufacturer's recommendation for 240Vac. I also bought lots of replacement fuses just in case:

Both the oscilloscope and the function generator work with 240Vac. Check:
That small bag of cables cost us $100. Ouch...

Now, the unfortunate items.

Here is a powered breadboard that I intend to bring. I've had this guy for several years for personal use. This box does NOT like 240Vac. In Mongolia, he MUST be powered by the step-down transformer. I checked that both +15V and -15V lines are able to source a 300-ohm resistor.

Now, I felt somewhat insecure bringing just one +/-15V source. So I obtained a bench +/-15V kit. Unfortunately, it also operates only on the 120Vac line.

Sanity check. Do things generally fit? I could benefit from another box once I wrap things more carefully...

Thursday, March 15, 2012

Teaching over Skype -- some thoughts

One of the observations that I have made after the first few lessons over Skype is that it is difficult to use the whiteboard effectively over webcam. In particular,

  • Writing is difficult to see, especially when the network connection becomes degraded (and video quality worsens);
  • There can be glare on the whiteboard surface;
  • The webcam shows only a very small amount of the board, and it can be tricky not to block the board, and to capture everything in the shot.
Due to these problems, I've noticed that it is useful to share the desktop screen instead, and to digitally display the circuit (and other diagrams) so that students can copy them down with ease. To this end, I've been using the MITx's built-in circuit simulator environment, but have found some alternatives that are also quite nice.

While browsing the web for some lightweight and friendly circuit diagram editors, I found CircuitLab (screenshot below) which turned out to be quite nice for my drawing purposes. Interestingly, the two guys who created CircuitLab are two former graduates from MIT (few years older than me) that I've met at the Institute!

Also a fairly massive solar panel (like a picture frame!) came in today:

Monday, March 12, 2012

MOS capacitor wafer

With thanks to former colleagues at MIT, I was able to get a hold of silicon wafers that with MOS capacitors (the basic structure underlying MOSFET transistors) that I can take on this trip. They originate from a course at MIT -- called 6.152 -- where students use MIT facilities for microelectronic fabrication. Here are some photographs of the wafer under the microscope:

(Interestingly, the 0.5 micron feature seems to act as a grating -- green reflections.)

Saturday, March 10, 2012

[6.002x] Lab photos

Dear all,

I thought that you might like to see the electronics lab that I will be bringing with me from the US: 
Over the next few months I will teach you how to build the circuits that you are studying in 6.002x as well as how to build other useful and interesting devices. I hope that you are excited!

The lab sessions will be as follows. Each of you will get into teams of 2 or 3, and I will meet with each team for 0.5~1 hour each week. Each team and I will build and discuss circuits together.

Also, please note that you have two assignments for MITx that are due on March 16th. They are:
  • "Basic circuit analysis" homework,
  • "Resistor divider" lab
Have a nice weekend!

Friday, March 9, 2012

Solar power

One of the things that I am most interested in demonstrating is solar power. Actually, this will be the first time that I personally try out a large-ish solar panel.

Wow. This panel can power through the regulator!

Things are arriving! (3)

The final batch of stuff that I ordered arrived today. All that's remaining are some cables from L-Com and more solar panels.

Things that are supposed to plug into the wall can take 240VAC:

One tricky thing: the function generator has an internal switch for setting 120/240VAC which is fine, but I did not purchase the replacement fuse for 240VAC yet.

This is some extra stuff that I have accumulated over the years that I will donate to the Sant school. It will be interesting if we could eventually do FPGA projects in Mongolia!

Let's see if things generally work.

1. Just reading the function generator output. Check.

2. Common source amplifier -- the basic piece of 6.002. Running on regulated batteries. Check. (Note to self: batteries on carry-on luggage, not check-in.)

3. See if the scope works with my radar (and that the radar still works...). Check! (The wiggles detect my moving of the hand in front of the radar transducers, i.e. the coffee cans.) I wonder if the TSA will let me take the radar...