Our friend and collaborator Eric Schlaepfer has been posting closeup photos of cross sections of familiar components in his twitter stream and they were recently highlighted in IEEE Spectrum. The photos are both beautiful and educational.
For the last year and a half, we’ve been volunteering with the Fremont Peak Observatory Association (FPOA). It is located in Fremont Peak State Park, just above the mission town of San Juan Bautista, which is where Hitchcock’s Vertigo was filmed.
Challenger (behind me in the picture above) is the name of the main telescope at FPOA. It is a 30 inch diameter Newtonian telescope on an equatorial mount, built by telescope maker Kevin Medlock. It is a lot of fun to move a big scope like this around to point it at different things in the sky. It is great for looking at deep sky things like galaxies, nebulas, and star clusters.
The members are incredibly welcoming and dedicated to amateur astronomy and science outreach. The organization has free (except for the state park parking fee) public programs on Saturday nights from March to October when there isn’t a full moon. The schedule for upcoming programs is posted on the website.
During public programs, we set up some of the smaller telescopes that belong to the observatory, and members sometimes bring their own telescopes to set up. This means there are usually multiple telescopes pointing at different things to see, and even folks who can’t use the ladder for the big Challenger telescope will be able to look to the stars.
It is a joy to be there the first time someone sees Saturn or Jupiter, or even the moon through a telescope. There is something special about seeing those things with your own eyes. The sky is dark enough—in part due to the ocean fog frequently socking in the towns below—that the viewing can be spectacular, and later in the year the Milky Way streaks across the sky.
Some members bring their gear up to the observatory to do astronomical imaging. We haven’t done any astrophotography other than cellphone photos through the eyepiece that don’t do justice to the view you get. We’ve seen incredible views of the planets, the Andromeda Galaxy, the Hercules Globular Cluster, the Ring Nebula and many other wonders. And perhaps best of all, we’ve had the privilege of sharing those views with visitors.
At the 2018 Bay Area Maker Faire, our project Uncovering the Silicon showed off a number of simple and complex integrated circuits (with rather large feature size) under the microscope. We had a great time helping visitors look at the features and get a glimpse of what’s inside those black box integrated circuit packages. To take this to the next level for this year’s Maker Faire, we decided to try and close the loop; to take one simple integrated circuit and elucidate its workings well enough that visitors to our booth will be able to see every single component of the circuit, understand their function, and relate it to the macroscopic behavior of the chip. For this, we picked what turns out to be a rather obscure chip: the Fairchild μL914, which is a dual 2-input NOR gate. This chip belongs to the resistor–transistor logic (RTL) family.
Here’s what the chip looks like. It’s in a funny old “glob-top” can package with eight leads.
Here’s the pinout; there are two NOR gates in the chip, plus power and ground.
Ken Shirriff built a circuit with the chip to demonstrate its functionality. When we push either of the two buttons for one of the gates, that LED will turn off.
Here’s the schematic diagram, adapted from the original datasheet. If you look at the left side, if either of those inputs goes high, the transistor pulls the output low.
John McMaster decapped a few of the chips and sent us a die photo. He made a video about the process — no small feat. We’ll be bringing one of these bare chips and a microscope (equipped with both eyepieces and a camera) to Maker Faire.
For the macroscopic scale, we approached visualizing this circuit from a couple of angles: the physical structure of the chip, and the electronic structure of the circuit.
Eric Schlaepfer used the die photo to model the structure of the chip in CAD.
Simultaneously, Ken designed a printed circuit board version for use with discrete components that maintained the same structure as the IC.
Working from Eric’s CAD model, we built a single NPN transistor model from layers of colored acrylic. If you lift it up, and look through the transparent middle layers, you can tell that the emitter (red) is embedded into the top of the base (yellow) and does not go all the down way through it. (Transistors like these are planar: The emitter is above the base, and the base is above the collector.)
The top layer of this little model has labels for the collector, emitter and base. It is removable so that the layers of the model can be more easily inspected.
The model of the chip die includes a transparent cover representing the oxide layer, and that supports the metal layer with the wire bond pads on the edges.
One of the reasons that this particular chip is educational to look at is that there are a few unused components on the die. There are two unused transistors: one of them is unconnected, and the other is shorted. There are also several unused resistors (resistors are the dogbone shapes). The unconnected and unused components are easier to see, and provide a visual example that is useful for understanding what the connected components look like under the metal layer.
It is also fun to imagine what other circuits could have been made with different connections.
We glued most of the layers together, but left the top two layers removable so that it is easier to see the internal structure when the top is removed.
(Aside: we left out most of the epitaxial pocket material, because even though we used transparent acrylic to represent it, the layers of the components are much more visible without it present.)
There are cutouts in the oxide layer where the metal layer connects to the circuitry below.
One of the most noticeable things you see when you look at this type of IC under the microscope is the bond wires. We’ve used silver glitter hot glue sticks to represent them.
The glob of melted glue represents where the wire is bonded to the pad.
When you look straight down on the model with its glitter bond wires, it looks very similar to what you’ll see in the microscope.
To round things out for our acrylic model, we made a physical legend to make it easier to identify all of the parts of the model.
Once Ken got his PCBs back from our friends at OSHPark, he built it up with the same example circuit.
The PCBs turned out beautifully, and it’s great to see the familiar discrete packages on the enlarged circuit. Ken has published the PCB design on Github.
We hope to see you at Maker Faire this weekend!
Bonus: Ken laid out some hypothetical alternate metal layers to use the same die to create different chips.
I will be at Science Hack Day SF giving a lightning talk on Creative Off-Label Tool Use featuring some of the cool and unusual ways people are using AxiDraw and other tools we make. I’ll also have an AxiDraw in the hardware hacking area to play with.
Science Hack Day is October 27-28 and is free, so register now!
P.S. If you’re doing something interesting and science or research related with your AxiDraw, please let me know!
The Annotated Build It Yourself Science Laboratory is featured on Cool Tools today!
This kind of bootstrapping science education is perfect for science museums, teaching labs, camps, and incredibly self-motivated kids.
I was thrilled to see the Touch Creature sculpture above by Talya Stein, especially after having seen an earlier version. She and I talked about the approachability of organic materials like wood. It was wonderful to see kids interacting with it.
I had a great conversation with Blythe Serrano, who I had met at a previous Maker Faire, about the material properties she has learned this year from experimenting with silicone casting. She makes light up pet collars, and generously shares her learning processes.
I loved this spatial magnetic field visualization by Inhye Lee. The three tubes in the center contain individually controllable electromagnets. The compasses spin in their spheres in response to the changing magnetic fields.
There are so many more I had the pleasure of connecting with and catching up with, including Becky Stern, Sophi Kravitz, Star Simpson, and Sally Byers. I love Maker Faire for the opportunity to bask in the glow (LED glow in some cases) of so many incredible women.
Windell will be giving a talk on Sunday at this year’s Maker Faire in New York.
You can catch the talk on Sunday, October 2, at 2:30 PM, on the Make: Show & Tell Stage.
I’ll be giving a talk and demo on Saturday at this year’s Maker Faire in San Mateo, CA. I’ll be demonstrating one of the many projects from my book, The Annotated Build-It-Yourself Science Laboratory (and signing books as well).
You can catch the talk and demo on Saturday, May 21, at 1:30 PM, on the Maker Show & Tell Stage.