Hackaday Interview: [Grant Imahara]

We had a chance to interview [Grant Imahara] at the 2014 Electronica conference in Munich, Germany. If you don’t recognize [Grant’s] name you’ll probably recognize his face. He’s been on the cast of the television show Mythbusters for about 10 years now. We heard recently that he was leaving the show and that’s how we crossed paths with him.

[Grant] has signed on with Mouser Electronics to promote their Empowering Innovation Together program. They hosted him on a press junket at their booth and since we have a good relationship with Mouser they offered Hackaday an interview slot.

We had a lot of fun talking to [Grant]. Unfortunately the wireless microphones the Mouser videographer was using were picking up a lot of interference. This didn’t directly affect our recording setup as we were using a handheld voice recorder, but we kept getting interrupted as they tried to figure out the problem. Still, as you can see from the video below, we managed to get all the way through a few questions about [Grant’s] introduction to electronics at a young age, his first job out of school working for Industrial Light and Magic, and his advice to others who want to get into electronics and specifically robots. He mentions his early learning was guided by the books of Forrest Mims and that these days learning about electronics is no more than a keyword search away.

Better SPI Bus Design

Quick, how do you wire up an SPI bus between a microcontroller and a peripheral? SCK goes to SCK, MISO goes to MISO, and MOSI goes to MOSI, right? Yeah. You’ll need to throw in a chip select pin, but that’s pretty much it. Just wires, and it’ll most likely work. Now add a second device. The naïve solution found in thousands of Arduino tutorials do the same thing; just wires, and it’ll probably work. It’s not that simple, and Mr. Teensy himself, [Paul Stoffregen] is here to show you why.

When using multiple SPI devices, a pullup resistor on the chip select lines are a really great idea. Without a pullup, devices will work great when used alone, but will inexplicably fail when used together. It’s not magic; both devices are listening to the bus when only one should be. Putting a pullup on the CS lines keeps everything at the right logic level until a device is actually needed.

How about the MISO line? Most peripherals will disconnect their pins when the chip select signal is active, but there are exceptions. Good luck finding them. There is an easy way to check, though: just connect two resistors so the MISO line floats to a non-logic level when the CS pin is high, and check with a voltmeter. If MISO is driven high or low, you should put a small tri-state buffer in there.

That just covers hardware, and there are a few things you can do in software to reduce the number of conflicts when using more than one SPI device. One of these methods is transactions, or defining the clock rate, setting MSB or LSB first, and the polarity of the clock. Newer versions of the Arduino SPI library support transactions and the setup is very easy. In fact, transaction support in the Arduino library is something [Paul] worked on himself, and gets around the problem of having SPI-related code happening in both the main loop of a program and whenever an interrupt hits. Awesome work, and a boon to the Arduino makers around the world.

Enhanced Coffee Brewer Knows How Much of a Caffeine Addict You Are

Who should chip in the most to restock the community coffee supply at work is a common point of contention at some offices. This RFID infused coffee brewer called Juraduino by [Oliver Krohn] solves the issue at his workplace once and for all by logging how much is being consumed by each person and how often; quite the diplomatic hack.

[Oliver] donated his old Jura Coffee maker to his office with some added hardware cleverly hidden underneath the faceplate of the machine. An Arduino mounted within runs the show, powered through mini USB from the logic unit of the coffee maker itself. Once a co-worker swipes their RFID card over the front of the machine, a real-time clock module stamps when the coffee was requested, and then logs the amount selected by that person on a mini SD card. The data stored is sent via an additional bluetooth module to a custom app [Oliver] created with MIT App Inventor for his phone which displays the information. These details can then be exported in the form of an email addressed to everyone in the office at the end of the week, announcing definitively who can be counted on to restock the bulk of the community supplies.

Though there isn’t a link available with further documentation, [Oliver] mentions in the ‘details’ portion of his video that he’d be happy to share that information with anyone who contacts him regarding the project. You can see the Jura at work below:

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A UV Lightbox For Curing Prints

With resin printers slowly making their way to hackerspaces and garages the world over, there is a growing need for a place to cure these UV resin prints. No, they don’t come out of the machine fully cured, they come out fully solid. And no, we’re not just leaving them in the sun, because that’s not how we do things around here.

[Christopher] whipped up a post-cure lightbox meant to sit underneath his Form 1 printer. It’s made of 1/2″ MDF, with adjustable feet (something the Form 1 lacks), a safety switch to keep the lights off when the door is open, and a motor to rotate the parts around the enclosure.

The light source for this lightbox is 10 meters of ultraviolet LED strips. The LEDs shine somewhere between 395-405nm, the same wavelength as the laser diode found in the Form 1 printer. Other than a bit of wiring for the LEDs, the only complicated part of the build was the motor; [Christopher] bought a 2rpm motor but was sent a 36rpm motor. The vendor was out of 2rpm motors, so a PWM controller was added.

It’s a beautiful build that shows off [Christopher]’s ability to work with MDF. It also looks great sitting underneath his printer, and all his parts are rock solid now.

Hacking the Crayola Digital Light Designer

[Harry] wrote in with his hack of the Crayola Light Designer. The Light Designer is a pretty unique toy that lets kids write on a cone-shaped POV display with an infrared light pen. [Harry] cracked one open and discovered it has a spinning assembly with a strip of 32 RGB LEDs for the display and a strip of photodiodes to detect pen position. These were ripe for the hacking.

The spinning assembly uses several slip ring connections to send power and data to the spinning assembly. [Harry] connected a logic analyzer to several of the connections to determine which lines were clock, data, and frame select (the strip is split into 2 16-led “frames”). He went on to reverse-engineer the serial protocol so he could drive the strips himself.

Instead of reverse-engineering the microcontroller on the product’s PCB, [Harry] decided to use a Leostick (Arduino Leonardo clone) to control the LEDs and spinner. He mounted the Leostick on the shaft of the spinning assembly, and powered it over the slip ring connections. After adding some capacitance to make up for noisy power from the slip rings, [Harry] had the POV display up and running with his own controller. Check out the video after the break to see the hacked POV display in action.

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Chicken-powered Pendulum

Every once in a while we get sent a link that’s so cute that we just have to post it. For instance: this video from [Ludic Science]. It’s a wind-up chicken toy that kicks a pendulum back and forth. No more, no less.

But before you start screaming “NOT A HACK!” in the comments below, think for a second about what’s going on here. The bird has a spring inside, and a toothed wheel that is jammed and released by the movement of the bird’s foot (an escapement mechanism). This makes the whole apparatus very similar to a real pendulum clock.

Heck, the chick toy itself is pretty cool. It’s nose-heavy, so that under normal conditions it would tip forward. But when it’s wound up, tipping forward triggers the escapement and makes it hop, tipping it backward in the process and resetting the trigger. The top-heavy chicken is an inverted pendulum!

And have a look, if you will indulge, at the very nice low-tech way he creates the pivot: a bent piece of wire, run through a short aluminum tube, held in place by a couple of beads. Surely other pivots are lower-friction, but the advantage of using a rod and sleeve like this is that the pendulum motion is constrained to a plane so that it never misses the chicken’s feet.

Our only regret is that he misses (by that much) the obvious reference to a “naked chick” at the end of the video.

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Simple Thermal Imager with a Lepton Module

[Andrew] designed a simple thermal imager using the FLIR Lepton module, an STM32F4 Nucleo development board, and a Gameduino 2 LCD. The whole design is connected using jumper wires, making it easy to duplicate if you happen to have all the parts lying around (who doesn’t have a bunch of thermal imaging modules lying around!?).

The STM32F4 communicates with the Lepton module using a driver that [Andrew] wrote over a 21MHz SPI bus. The driver parses SPI packets and assembles frames as they are received. Images can be mapped to pseudocolor using a couple different color maps that [Andrew] created. His code also supports min/max scaling to map the pseudocolor over the dynamic range present in the image.

Unfortunately the Lepton module that [Andrew]’s design is based is only sold in large quantities. [Andrew] suggests ripping one out of a FLIR ONE iPhone case which are more readily available. We look forward to seeing what others do with these modules once they are a bit easier to buy.