Logic Noise: Ping-pong Stereo, Mixers, and More

So far on Logic Noise, we’ve built up a bunch of sound-making voices and played around with sequencing them. The few times that we’ve combined voices together, we’ve done so using the simplest possible passive mixer — a bunch of resistors. And while that can work, we’ve mostly just gotten lucky. In this session, we’ll take our system’s output a little bit more seriously and build up an active mixer and simple stereo headphone driver circuit.

For this, we’ll need some kind of amplification, and our old friend, the 4069UB, will be doing all of the heavy lifting. Honestly, this week’s circuitry is just an elaboration of the buffer amplifiers and variable overdrive circuits we looked at before. To keep things interesting we’ll explore ping-pong stereo effects, and eventually (of course) put the panning under logic-level control, which is ridiculous and mostly a pretext to introduce another useful switch IC, the 4066 quad switch.

At the very end of the article is a parts list for essentially everything we’ve done so far. If you’ve been following along and just want to make a one-time order from an electronics supply house, check it out.

klangoriumIf you’re wondering why the delay in putting out this issue of Logic Noise, it’s partly because I’ve built up a PCB that incorporates essentially everything we’ve done so far into a powerhouse of a quasi-modular Logic Noise demo — The Klangorium. The idea was to take the material from each Logic Noise column so far and build out the board that makes experimenting with each one easy.

Everything’s open and documented, and it’s essentially modular so you can feel free to take as much or as little out of the project as you’d like. Maybe you’d like to hard-wire the cymbal circuit, or maybe you’d like to swap some of the parts around. Copy ours or build your own. If you do, let us know!

OK, enough intro babble, let’s dig in.

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Your Brain Thinks Its Burning You, But It’s Not

In the cult classic Dune, there’s this fictional device called the “Pain Box”. If you touch it, you’ll feel like your hand is burning, but in reality, no tissue is being damaged. In the real world this is called the Thermal Grill Illusion, which was discovered back in 1896. Much to our chagrin, [Adam Davis] has just finished building a working prototype.

Sound familiar? We covered a similar project a few months ago — but unfortunately it didn’t work very well. Luckily, and boy do we love it when this happens, [Adam] saw the post, and got inspired to try it himself. He had actually designed a system years back but never got around to building it. Upon seeing the post — and the difficulties in making it work — he just had to figure it out.

So how does it work? The Thermal Grill Illusion uses alternating warm and cool bars which stimulate the temperature receptors in your skin — and confuse them. Neither the warm or cool bars are extreme enough in temperature to do any harm, but your confused little temperature receptors make it feel like you’re either burning or freezing your skin off!

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Digital Counter From Stuff You Have In Your Junk Drawer

In vehicle racing, a properly tuned suspension is essential for making good time around the track. Weekend Race Warrior [Julian], thought that his right rear suspension might be bottoming out when making hard left turns. After thinking about it for a while, he came up with a super simple way to measure how many times his suspension bottoms out during a lap: a digital counter made from a calculator.

There are two types of calculators out there, one is good for this project and the other won’t work. To figure out which one you have, type in 1+1=. All calculators should display 2. Then, press the = button again. Some calculators will continue to show 2, but some will change to 3, then 4 and so on as many times as the = button is pressed. This is the type of calculator this project requires.

[Julian] opened up his calculator and soldered a pair of wires across the = button terminals. After a hole was drilled in the case for the wires to exit, the calculator was put back together. To count how often his suspension bottomed out, a normally open limit switch was installed on the car at a point where it would be triggered when the suspension bottomed out. The 2 added wires coming out of the modified calculator connect to that switch. Switch presses now emulate a = button press. Before starting a lap, 1+1= is pressed to display 2. At the end of the lap, if the suspension bottomed out, the switch would be triggered and the displayed value would increase. Remember to subtract 2 from that value to get the total number of events that occurred.

A mechanical switch makes this a great application for counting when things move a certain way but there are some more options. Connecting the switch-side of a relay to the calculator allows [Julian] to count brake presses (via the break light signals) or count how often his boost pressure goes over a certain amount (using a pressure switch).

Blinking LEDs For A Timeless Fountain

We’ve seen a few of these builds before, but the build quality of [Mathieu]’s timeless fountain makes for an excellent display of mechanical skill showing off the wonder of blinking LEDs.

This timeless fountain is something we’ve seen before, and the idea is actually pretty simple: put some LEDs next to a dripping faucet, time the LEDs to the rate at which the droplets fall, and you get a stroboscopic effect that makes tiny droplets of water appear to hover in mid-air.

Like earlier builds, [Mathieu] is using UV LEDs and is coloring the water with fluorescein, a UV reactive dye. The LEDs are mounted on two towers, and at the top of the tower is a tiny, low power IR laser and photodiode. With the right code running on an ATxmega16A4, the lights blink in time with the falling water droplet, making it appear the drop is hovering in midair.

Blinking LEDs very, very quickly isn’t exactly hard. The biggest problem with this build was the mechanics. The frame of the machine was machined out of polycarbonate sheets and went together very easily. Getting a consistent drip from a faucet was a bit harder. It took about fifteen tries to get the design of the faucet nozzle right, but [Mathieu] eventually settled on a small output hole (about 0.5 mm) and a sharp nozzle angle of about 70 degrees.

[Mathieu] created a video of a few hovering balls of fluorescence. You can check that out below. It’s assuredly a lot cooler in real life without frame rate issues.

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Brass Clock Face Etched With PCB Techniques

Over the last few months, [Chris] has been machining a timepiece out of brass and documenting the entire process on his YouTube channel. This week, he completed the clock face. The clock he’s replicating comes from a time before CNC, and according to [Chris], the work of engraving roman numerals on a piece of brass would have been sent out to an engraver. Instead of doing things the traditional way, he’s etching brass with ferric chloride. It’s truly artisan work, and also provides a great tutorial for etching PCBs.

[Chris] is using a photoresist process for engraving his clock dial, and just like making PCBs, this task begins by thoroughly scrubbing and cleaning some brass with acetone. The photoresist is placed on the brass, a transparency sheet printed off, and the entire thing exposed to four blacklights. After that, the unexposed photoresist is dissolved with a sodium carbonate solution, and it’s time for etching.

The clock face was etched in ferric chloride far longer than any PCB would; [Chris] is filling these etchings with shellac wax for a nice contrast between the silvered brass and needs deep, well-defined voids.

You can check out the video below, but that would do [Chris]’ channel a disservice. When we first noticed his work, the comments were actually more positive than not. That’s high praise around here.

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Pneumatic Multiplexer

This is a pretty cool project [Sebastian Morales] is working on – a 3D printed Pneumatic Multiplexer. Large interactive installations, kinetic art and many other applications require large numbers of actuators to be controlled. For these type of projects to work, a large number of actuators equals higher resolution and that allows the viewer to be captivated by the piece.

The larger the system becomes, the more complex it becomes to control all of those actuators. [Sebestian] wanted to move a large number of components with a relatively low number of inputs. He thought of creating a mechanical equivalent of the familiar electronic X-Y matrix that can control large quantities of outputs using only a few inputs – in a more descriptive form, Outputs=(Inputs/2)^2.

airlogic_01He looked at chemical reactions that change liquids in to gases, but that seemed pretty complicated. Refrigerants used in air conditioning looked promising, but their handling and safety aspects looked challenging.

Eventually, he decided to look at using “air logic“. Air logic uses pneumatic devices to create relays, limit switches, AND gates, NAND gates, OR gates, amplifiers, equivalent to electrical circuits. Electrical energy is replaced with compressed air. His plan was to build a multiplexer whose elements would open only if the combination of pressure between both lines was the right one. As in electronics, NAND logic is easy to implement. A moving element creates a seal and only allows air out if the bottom line was low and the top line was high.

He had access to a high resolution, resin based 3D printer which allowed him to create fully air-tight systems. He started with prototyping a small 4×4 matrix to test out his design, and had to work through 6 to 7 iterations before he could get it to work. The next step was to create a larger matrix of 100 elements controlled by 20 inputs (10×10 matrix). He created Omnifarious – a kinetic sculpture demonstrating the concept of shapeshifting objects. The Omnifarious is a hexecontahedron which would be able to transform its surface to render different geometries via 59 balloons on its surface. Below, you can check the videos of his progress building the various prototypes and another video showing the Omnifarious sculpture.

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Steering High Altitude Rockets With Cold Gas

Amateur rocketry has been popular for ages, with designs ranging from small toy-scale model rockets to large-scale liquid fuel designs with steerable fins. A team out of Portland State works on some large-scale amateur rockets that can fly to very high altitudes. Since the atmosphere is thin the further the rocket flies, steering fins aren’t incredibly effective once the rockets reach high altitude. A team of students tackled this problem by designing a cold-gas reaction module to steer high-altitude rockets.

The team chose nitrogen as their cold-gas propellant, which is stored in a carbon fiber tank. After passing through a regulator, the gas is routed to several gas solenoids and then to a custom 3d-printed de Laval nozzle. An Intel Edison is used to drive the system, which calculates the rocket’s orientation with a MPU-6050. Control loops use the orientation information and fire gas through any of several nozzle ports to steer the rocket.

The system does have some limits: the solenoids are either on or off, not variable, and they aren’t incredibly fast. Even with these limitations, the team is confident that their module will work great when it embarks on its maiden flight in a brand-new custom rocket next year. The team was also awesome enough to make all of their design files open-source so you can build your own (although they warn that it’s a bit complicated and dangerous). Check out the video after the break to see a test-run of the cold-gas reaction system.

Thanks for the tip, [Nathan]!

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