Category Archives: Electronics

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:




Another take on Twisted Wire Bundles

Steve W. wrote in to share his improvement on the method for making wire bundles we wrote about:

 I’ve used the bend-it-over-and-stuff-it-in-the-chuck approach, but was not fully happy with it.

Binder clip on wood piece for drilling

So I drilled a 1/8″ hole in the back of a binder clip.  The drilling is easy if you clip a ~3/8 scrap of wood.

Wire twisting jig in drill chuck.

A 4-40 SHCS screw long enough to allow me to actuate the clip was not threaded all the way to the head, so I used a 1/4″ spacer between the binder clip and the 4-40 nut.  (Pan head screws are usually 100% threaded, but I would have had to look in the dreaded ‘other’ box to find one of those). Having the nut up against the chuck acted as a lock-nut.  I had been surprised when I first tried this that I did not have to work harder to keep it from loosening.  I had expected I might need a lock washer, and/or a second nut to lock the first.

Just grabbing the wires with the binder clip (my original plan) was not secure.  So I wrap the wires 180 degrees around a screwdriver bit and put that in the clip.

Works great, and it is quick to pop in and out when twisting many groups of wires.

Thanks for sharing your hack and sending the photos!

Analog Education and the 555

The article Can Analog Circuits Inspire Budding Engineers? over at Planet Analog discusses preparing students for dealing with real world circuitry by getting them started with analog circuits.

By building, probing, and observing the signals and their changes in these circuits without any code requirements, students can get a real feel for otherwise abstract concepts such as voltage, current, and more.

The author uses examples of projects and kits including our very own Three Fives Kit.

Blinky AVR Earrings

Blinky AVR Earring

Look what just arrived in the mail– Blinky AVR Earrings!

Blinky AVR Earrings

Not long ago, Rick posted on twitter about the ATtiny84 blinky earrings he had made, inspired by my voltage regulator earrings (which I now fasten on with the appropriate phillips screw).

Four blue LEDs blink in sequence, powered by a CR1220 battery. The board is traditional OSHPark purple, with an ISP header for convenient reprogramming. They’re lighter than they look and quite comfortable.

Thank you, Rick! I know what I’ll be wearing to Maker Faire!

From the Mailbag: Interactive Game of Life

Game of Life by Forrest

Forrest shared these pictures of his Interactive Game of Life build.

I bought the project to help expose my two grandsons to electronics and learn how to build circuit boards.  Dan my 10 year old did one board all by himself just using your instructions. Josh my 14 year old did more than half of the boards and I finished them up because I only have the kids for limited time periods. I am so proud of them. Josh complete understands how the Game Of Life works…I don’t  HA!  We are planning on adding a instruction board to the bottom of the display so other kids can have fun.

I have a CNC router and built the frame.  The boards are screwed onto a piece of 1/4″ plywood which floats in the frame.  Not glue in.  I machined a loose slot around the inside frame pieces.  That way I can take the frame apart and easily change out of a board if necessary.  It has been so much fun to build and you have SUPER service.

We thank you so much and would like to build more projects that you may come up with.  As soon as I get more time with Dan we are going to build the clock.

He also shared his case design (105 kb dxf). Thank you for sharing your time and skills with your grandkids, and for sharing your pictures and design with the rest of us!

Meggy Jr RGB + WaterColorBot

Meggy Jr RGB controlling WaterColorBot

Our friend Schuyler hooked up our Meggy Jr RGB hand-held video game platform up to control the WaterColorBot. He wrote on twitter:

I got the @EMSL Meggy Jr RGB working with the @MakerSylvia WaterColorBot. My code is here.

WaterColorBot art made using Meggy Jr RGB

The output looks great, too. Thanks for sharing your code, Schuyler!