Mathematica on the raspberry-pi – a library class

I really like teaching classes through Workshop 88 at the libraries.  Over the summer, I had a chance to teach a few of the classes Workshop 88 offers at some of the local libraries. One library that we like going to wanted a class to introduce their teens and preteens to the Raspberry Pi.

I recruited a few helpers and we gathered up several Raspberry Pis, keyboards, mouses, and power supplies to have enough supplies that the kids would be working in pairs or at their own Raspberry Pi.  We set up before the kids arrived and had everything ready to go. At the start of class we talked about the idea of the Raspberry Pi as a low-cost single board computer and we pointed out all the hardware features of the Pi.  Then we showed off all of the distributions that we had brought examples of.

That took all of 25 minutes for a 90 minute class. Oops.

So, I asked how many of the kids were familar with Scratch, and it turned out that more than half of them had already used Scratch in school.  I decided that they should get a chance to work with Mathematica, so that they would be exposed to something new.

There is a pretty good introduction to Mathematica for the Raspberry Pi on the Raspberry Pi Foundation website. (The actual Mathematica tutorial starts here.)

We did a bunch of things that I think worked really well:

1.) Showed basic math operations
2.) Showed how to make graphs
(One of the kids said at this point that Mathematica is basically just a less powerful calculator. That’s when we kicked it up a notch.)
3.) Kids explored how many digits of pi they could get out of Mathematica.
4.) Kids played with displaying 3D shapes using the Graphics3D function. Examples: Graphics3D[{PolyhedronData[{Antiprism, 4}, “Faces”]}]
Graphics3D[{Opacity[.4], Glow[RGBColor[1, 0, .5]],
PolyhedronData[“JessensOrthogonalIcosahedron”, “Faces”]}]
5.) Kids played with 2D shapes.  Examples: Graphics[Polygon[{pentagon, 1 + .5 pentagon, 1.5 + .2 pentagon}]]
hexagon = Table[{Sin[2 Pi n/6], Cos[2 Pi n/6]}, {n, 6}]
Graphics[Polygon[hexagon]]

Lastly, we tried to generate some sound files with Mathematica, but it didn’t seem to work too well on the Raspberry Pis.

Overall, I think the kids had a great time playing with Mathematica and trying out a bunch of things that they had no idea a $35 computer could do.

 

Tesla Coil demonstration on September 17!

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Workshop 88 member Phil Strons will be giving a demonstration of his Tesla coil at Workshop 88 this coming Saturday, September 17th, from 1:00 to 5:00pm.

Here’s what Phil has to say about what to expect from this demonstration: “Last year I had 20-inch sparks, but I’ve since done some modifications & repairs. I’m hoping for closer to 30-inch long sparks this time.”
WARNING – This device generates electric fields with high voltages of 1,000,000 Volts or more and has potential to interfere with medical devices such as pacemakers.

tesla-coil-demo-promo-photo

A member review

A member of the Workshop 88 mailing list posted a review of a new sewing machine she recently acquired.  With her permission, we’re posting it here:


Sewing Machine Review

Janome /  New Home Derby 1/2 Size, 10 basic stitches
I purchased this as a second machine, because it is simple, small, and very light — the opposite of my complex computerized full-size heavy motor Elna 9000 machine.
     Don’t get me wrong, I still love the Elna.  Truly.  But the idea of an ultra portable machine, that I could take along when I’m meeting up with other crafters had a lot of appeal.  And then I saw the Derby models online at Amazon, in 10 beautiful color choices, and it was time to save up my coins to get one.
     What’s in the box?  The sewing machine itself, user manual,and a small plastic bag containing the foot pedal, power brick/cord, 2 spare bobbins, 1 spare needle, and a needle threader.
     Setup:  It took only about 5 minutes to unpack, plug in, thread up the machine to wind a bottom full of thread, load the bobbin into the machine, and rethread the machine for sewing.  The threading diagrams were clear and instructions straight forward.
     Sewing:  Ok, the machine was ready, and it was time to sew.  I started with a piece of polarfleece.  I was turning the raw edges of the fleece over to give a stadium blanket a nice solid hem, so I was using the largest zig zag stitch, stitching through 2 layers of polar fleece.  I left the upper and lower tension on the factory presets. Unlike most machines, the foot pedal does not control sewing speed; it’s more of an on-off switch. There is only one speed. This feels a little weird when you’re used to speed control, but isn’t bothersome once you’ve sewn for 10 minutes or so.  Overall, the machine was smooth and even, and less noisy than I expected from a primarily plastic machine.  The machine had no problem sewing the polar fleece, and the feed dogs advanced the fleece evenly.
     Switching to cotton fabric, the machine breezed through a a simple seam. Next I sewed in a zipper.  The machine has no zipper foot, but it does have one stitch that moves the needle to the far left position so you can sew alongside the zipper coil.  It was old school sewing, but it got the job done.
     Next I sewed a cotton panel onto a sturdy canvas bag. It required sewing through the tough canvas (multiple layers) and seams. It required using the reverse stitch, straight stitch, and using the free arm to sew “into” the bag. (The cotton band creates a set of organizer pockets on the outside of the bag, and the fabric adds a nice accent.)  I was concerned that the small size of the machine would make it hard to sew things that are complex shapes (not flat) and that need to be stitched “inside”.  The machine passed with flying colors!  Janome / New Home did a good job designing the machine so that there is ample clearance, so you can sew things like cuffs, collars, and other items that are dimensional. The machine handled the medium weight canvas well, even up to 3 layers.  But I would not recommend the machine for sewing heavier materials than that, because of the power limitations of the machine.
     Pluses:  The machine is really cute, and very light.  It sews well.  It meets all expectations.
     Minuses:  There is no built in light, so you might want a portable lamp to help see during needle threading.  The machine has only one speed, which takes a little getting used to.
     Overall: 4.5/5.0  Would recommend as a second machine, or a starter machine.

W88 at Southland Mini Maker Faire

Andrew+Kids5559Andrew and Jim represented Workshop 88 at the Southland Mini Maker Faire in Mokena August 27th.  That Faire is run by Jay Margalus, one of Workshop 88’s founders.

Andrew’s workshop for kids to create their own hand-dipped paint-film artworks was a big hit, with dozens of delighted artists taking home their masterpieces.  Foam balls were the canvas; a bucket of water was the studio.

spray_paint_1024AThe technique, invented by Andrew using a film of spray paint on a tub of water, was inspired by a similar approach he’d seen using nail polish.  Less-than-perfect results with the polish caused him to test and perfect the paint approach.  Results were spectacular.

The laser toys box was there, as TrayAndLizardsCq65vvhW8AADHjVusual, and its Escher lizards provided entertainment and education for many little (and not-so little!) hands.  Having the back sides of the laser-cut pieces engraved with three different patterns provided an additional level of challenge based on the 3-way tessellation as a 3 color map problem.  The laser engraved wording on what used to be the bottom of the tray used to be obscured by the toys.  With the addition of the new slightly smaller lower box, that old tray is now both a useful top cover and a convenient display card!

GearsCq6wHU5XgAAxTWC-600Jim’s UV-lit fluorescent non-round gears caused lots of folks to stop and take a look.  Their graceful turning, speeding up, slowing down, reversing and repeating mesmerized a few visitors.  Their stepper controller and Tiny85 processor mostly worked, but required some discreet wiggling several times to keep it all going.  The flaky solderless breadboard that hosted them has since been replaced by a much more reliable dedicated PCB.

Display+TabletHis hexagonal WS2812 individually addressable RGB LED wall display made its debut as an actual interactive device at this Faire.  Controlled by a 16-button app on an Android tablet, connected via Bluetooth to a cheap radio on the Arduino that runs the display, the display was fun to make dancing patterns with to music from a small sound system on the table.  Next upgrade will be a better drum pad app with velocity and aftertouch, and lots more controls.

Thanks and a tip of the W88 hat to Drew Fustini for some of these pictures!

 

T-Kit 1380 Kit Build: Part 2

Today, I’ll be continuing my 80m transceiver build that I started in T-Kit 1380 Kit Build: Part 1.

At the end of the last post, the board looked like this:

The full board

The full board

Today I’ll be moving on to the VFO section of the board.  A VFO, or variable frequency oscillator, is the circuit that allows you to tune a radio.  This particular VFO is based on a Collpits oscillator, and can tune over a 50-70 kHz range centered on a frequency determined by the component values.  The frequency range shown in the image may seem a bit strange.  This transceiver can be built to cover that 50-70 kHz range somewhere near 3.5 MHz to about 3.75 MHz.  The short explanation is that the frequency we’re interested in is shifted by the frequency of the VFO to an intermediate frequency of 8 MHz, where we can do filtering and amplification at a single fixed frequency.  Since a lot of circuit characteristics are frequency-dependent, performance is much better if the components can be selected for just one frequency.

schematic

The majority of the components are supplied with the kit, so their values are fixed.  One of them, an inductor, I had to wind myself.  Since this phase required quite a few components, I decided I’d lay them out before I started.

components

Rather than start building immediately, I decided to wind the inductor first, so I could get that out of the way.  The instructions specified 28 turns of the green #28 enameled wire on the red toroid core.  I had to count the turns several times to be sure.

inductor

The inductance of the coil is dependent on a lot of things, including the material the core is made of, the diameter of the core, the number of windings, and the spacing between the windings.  Later on in the build, I tweak the range covered by the transceiver by adjusting the coil spacing.

phase-2-complete

From this point on, it was simply a matter of stuffing the board and soldering, as per the instructions.  The one thing I would have changed was the process for doing initial testing of the inductor.  They have you tack a couple leads to the pads you’re going to use, and then tack the inductor to those.  Unless your inductor is wildly off, you’re not going to be rewinding it, so I would have skipped that step and just soldered it in directly at the beginning.

The testing of phase 2 was relatively simple, because I’m using a frequency counter.  I just hooked up the frequency counter, and adjusted the spacing of the turns on the coil I mentioned before until the VFO covered the range between 4.470 MHz and 4.391 MHz.

I’ll talk more about it in the next post about the transmit mixer and filter, but that provides an actual range of 3.530 MHz to 3.609 MHz.  This includes the QRP CW calling frequency at 3.560 as well as W1AW’s code practice sessions transmitted on 3.5815.  It does not include the main CW DX window between 3.500 and 3.525 MHz, but I’m still working on getting my Amateur Extra license, so I’m not authorized for that part of the band anyway.

 

T-Kit 1380 Kit Build: Part 1

I won a T-Kit 1380 80m 3 watt CW transceiver kit at the WCRA Hamfest back in 2014, and it’s been sitting on my bench unopened since then.  I didn’t have my license at the time, but I got my General license about a week later. I decided that this summer was a good time to start building it. Here’s a link to one you can pick up if you’re interested : http://www.rkrdesignsllc.com/-13/

I have quite a lot of kit-building experience, but most of it is digital electronics, so this is probably the most complex kit I’ve ever built, both in number of components and circuit complexity.

If you’re not familiar with amateur radio, this kit will let you transmit and receive on the 80m band (between 3.5 and 3.75 MHz) using CW (morse code).

1380 Manual

The schematics in the manual are a bit low-res, but the instructions for assembly are very good.  My biggest complaint with the manual so far is that errata are supplied as a stack of papers inside the manual.  Some of them referenced parts this kit doesn’t use, so it was a bit of a chore to go through and update the instructions and update the steps by hand.

The assembly process is documented in phases, with testing procedures at the end of each phase.

Phase 1 is construction of the DC input circuitry as well as the keying circuit.  The keying circuit is connected to the code key, and disables the receive circuitry while transmitting.  Here’s the diagram for phase 1.

Phase 1 schematic

Phase 1 schematic

Here’s the board as assembled:

Phase 1 assembled

Phase 1 assembled

This is a pretty densely packed board, and the silkscreen suffers for it.  The manual gives pretty decent drawings of the section of the board each phase is concerned with, and this helps quite a lot.  You can usually locate a component by finding a nearby component you’ve already installed, or one whose silkscreen isn’t broken up by a pad.

Once this phase was assembled, there was a short test procedure to verify that it is operating correctly.  Essentially, I had to apply 12v to the 12v input, and then verify that R13 (the resistor in the center of the board, just between the two beige ceramic capacitors) read 0v while the key wires were disconnected (the white and black wires just under ‘J1’), and 12v while they were touched together.

I misread the directions and it took me a while to figure out what I was doing wrong (I was measuring voltage drop across the resistor, not between the resistor terminal and ground), but in the end, everything checked out.

The full board

The full board

As you can see, there’s quite a lot of work still to do, so come back next time, when I move on to assembly and testing of the VFO section!

Surface-Mounted LEDs for LEGO & LED Inventing Camp

PlacingParts0270Rachel and Jim made up some very skinny surface mount LED/resistor strips that fit between Lego posts for a STEM camp Rachel is running.

A simple pattern was etched on flexible copperclad Kapton film, using vinyl from the vinyl cutter as resist.  Solder paste blobs and the tiny 0805 components were hand placed, ReadyToSlice0273then reflow soldered on the hot plate.  Here are some ready to be sliced apart.  The resulting glowing Gummi bears were a big hit with the kids!

EllaHead180514Campers beta-tested Rachel’s Conducty Inventing Kit during a week-long Spring Break camp at Moore Toys and Gadgets in Wheaton. They built circuits Cooper134906581directly on LEGO baseplates using conductive tape and components designed to fit between the LEGO studs. Kids lit up everything from Minecraft torches to outdoor campfires made of LEGO. Here, Cooper and Ella show off their creations.  The Conducty LED Inventing Kit will be launching on Kickstarter later this Spring.

We’re Hackerspace Passport Ready!

PageWstamp3788Thanks to the laser cutter, we now have an official rubber stamp, and we’re ready to provide Workshop88 visit chops to all our visitors with Maker Passports!  OK, as soon as one shows up.

Stamp3787But we now have the capability to make our own precision rubber stamps!  Rubber stamps.  Yeah, like in the paper-based olden days.  Well, I thought it was cool.

Some more details here.