All posts by Windell Oskay

About Windell Oskay

Co-founder of Evil Mad Scientist Laboratories.

XL741: Principles of Operation


Our two “dis-integrated circuit” kits are the Three Fives Discrete 555 Timer, and the XL741 Discrete Op-Amp. These two kits are functional, transistor-level replicas of the original NE555 and μA741 (respectively), which are two of the most popular integrated circuits of all time.

Last year, we wrote up a detailed educational supplement for the Three Fives kit, that works through its circuit diagram and discusses its principles of operation down to the transistor level. Today, we are doing the same for the XL741 kit, and releasing an educational supplement that explains how a ‘741 op-amp IC works internally, down to its bare transistors and resistors:

XL741 Documentation (PDF)

This ability to peek inside the circuit makes the XL741 a unique educational tool. In what follows, we’ll work through the circuit diagram, discuss the theory of operation of the ‘741 op-amp, and present some opportunities for experiments and further exploration.

You can download the supplement here: XL741 Principles of Operation (1.1 MB PDF)

Additional Resources:




Linkdump: June 2015

A Lego Mosaic Printer

JK Brickworks made this amazing “pick and place” style Lego Mosaic Printer:

It is built entirely using LEGO parts. It first uses the EV3 colour sensor to scan the source image and save the data on the Mindstorms unit. It can then print multiple copies from the saved image data. The 1×1 plates used for ‘printing’ the mosaic are supplied using a gravity feed system and the printing head is simply a 1×1 round plate that can pick up and place the 1×1 plates.

More information about this project can be found at JK Brickworks.

Politicians To Poop: A Chrome extension

Politicians To Poop

Politicians To Poop is a new extension for the Chrome web browser that replaces the names of presidential candidates (US, 2016) with the “pile-of-poo” emoji. Options allow you to “poopify” the names of Democrats, Republicans, or both.

Politicians To Poop is available now, for free, at the Chrome web store.


Politicians To Poop

Politicians To Poop

Politicians To Poop

Possible reasons that you might want to use this extension include:

  • You are from outside the US, and don’t need to hear these names every day.
  • You are temporarily overloaded by the amount of poop that the candidates sling at one another.
  • Because it is funny.

No judgement upon any of the named individuals, nor their platforms, parties, or beliefs is either implied or intended. This is intended to be an equal-opportunity text replacement tool, for the good of all humanity.

More information:
This project was inspired by Millennials to Snake People. Much more information including source code, the list of names, and additional attribution is available at our GitHub repository.

The books are in!

Build It Yourself Science Laboratory

The Annotated Build-It-Yourself Science Laboratory has arrived! We’ve got them in stock and are now offering signed copies at our store, too!

“Would you like to know more?” I’ll be speaking about the book at Maker Faire this weekend, on the DIY stage. Scheduled times are Friday at 2:30pm, Saturday at 10:30am, and Sunday at 4pm.

The Annotated Build-It-Yourself Science Laboratory

The Annotated Build It Yourself Science Laboratory

We have a book coming out!

Coming soon: The Annotated Build-It-Yourself Science Laboratory is a new, updated version of Build-It-Yourself Science Laboratory, the classic 1960’s hands-on science book by Raymond E. Barrett.

The book is scheduled to make its debut at Maker Faire next week, where I’ll be speaking about it. It’s also available for pre-order now from and other sellers of books, as well as from our store.

We’ll be writing much more about the book once it’s out— about what’s in the book, the process of updating and annotating it, and about the hundreds of project ideas spanning biology, geology, chemistry, physics and more.

However, since we’re already in teaser mode, here are some photos of the original version from the 1960’s:




Fine print: “You can build these and many other experimental items with materials from your home, garage, or local hardware store. Build-It-Yourself Science Laboratory will show you how!”

The Annotated Build It Yourself Science Laboratory


Linkdump: April 2015

The Clouds of Orion the Hunter

Hands on with NanoBeam


Last fall we wrote about NanoBeam, a new super-miniature open source aluminum T-slot profile construction set that was on Kickstarter at the time. While comparable in design to industrial profile systems like 80/20, its cross section of just 5 mm × 5 mm is comparable to a stud on a lego brick.

We recently got our tweezers hands on a ‘beam, and yes, it’s real, yes, it works, and yes, it’s that tiny. And just wait until you see the fasteners.

Continue reading Hands on with NanoBeam

Linkdump: March 2015

A Wax Coupler for EggBot

This tiny little thing is a new EggBot accessory that we call the Wax Coupler. Not because it’s made of wax (it’s CNC machined aluminum) but because you can use it to attach an egg to the motor that turns it, using wax, like so:


Aside: why is the base of the egg black? We’ll get to that below.

Once the egg is attached to the Wax Coupler, it provides a rigid attachment point that provides secure coupling between the egg and the motor. More importantly, the coupler+egg assembly can be removed from the motor and put back in place, without losing registration.  In machine tool terms, you might describe this as the process of attaching an egg to a rigid mandrel.


Wait– why would you want to do that?

Hardware 1 Pysanky eggs

Let’s go back a few steps. Last spring we introduced our Electro-Kistka for EggBot. A kistka is a hot-wax pen used in the traditional wax-resist and dye (batik) method to produce colorful eggs in the fashion of Ukranian pysanky, and this one is designed to work with a computer-controlled EggBot.

At the time, we noted that this process introduces a new problem, that of re-indexing the egg within the EggBot, after taking it out for dyeing:

It is harder than it looks.  While two-tone eggs are straightforward, we have found it to be challenging to precisely reposition an egg after removing it for dyeing. Thus, it takes considerable patience and experience to produce multicolor eggs with good registration between subsequent color layers.  We’d be interested in exploring better ways to do this.

Kistka-brush 7

One method that we tried (shown above) was to dye the egg in place, by brushing it without removing it. The results were mediocre: it worked, but the dye layers were subdued and blotchy. We also looked into a somewhat wackier method of dying the egg in place, by standing the EggBot on end, and using a collapsable bag of dye.

Which brings us to the proper solution: To attach the egg rigidly to a repositionable coupler with beeswax. Doing so allows us to take out the egg and dye it (coupler and all) and then easily index it back into the EggBot.

Continue reading A Wax Coupler for EggBot