Ketan's Home

June 25, 2016

WiFiRGB – A WiFi-enabled RGB high-power LED

Filed under: Uncategorized — ketan @ 8:58 AM


Tom blogged about his WiFi/Browser controlled RGB LED project:


  • Simple hardware, using pre-fabricated modules
  • Controls an RGB LED via any recent browser, any operating system
  • WiFi credentials can be configured via browser
  • Software is written as an Arduino sketch

Full details at Tom’s blog.

Check out the video after the break.

from Dangerous Prototypes

June 22, 2016

What is a Digital Product?

Filed under: Uncategorized — ketan @ 7:49 AM

As product managers and product owners, the products we look after are fundamental to our work: they shape our day-to-day activities and determine our responsibilities. We create a product strategy and product roadmap; we manage the product backlog and use minimum viable products and product increments. But what is a product? While this seems a …

from Java Code Geeks

June 21, 2016

How Lasers Actually Work

Filed under: Uncategorized — ketan @ 6:40 AM

Lasers are optical amplifiers, optical oscillators, and in a way, the most sophisticated light source ever invented. Not only are lasers extremely useful, but they are also champions of magnitude: While different laser types cover the electromagnetic spectrum from radiation (<10 nm) over the visible spectrum to far infrared light (699 μm), their individual output band can be as narrow as a few µHz. Their high temporal and spatial coherence lets them cover hundreds of meters in a tight beam of lowest divergence as a perfectly sinusoidal, electromagnetic wave. Some lasers reach peak power outputs of several exawatts, while their beams can be focused down to the smallest spot sizes in the hundreds and even tens of nanometers. Laser is the acronym for Light Amplification by Stimulated Emission Of Radiation, which suggests that it makes use of a phenomenon called stimulated emission, but well, how exactly do they do that? It’s time to look the laser in the eye (Disclaimer: don’t!).

The Optical Amplifier

When we talk about the amplification of electrical signals, we are typically not too concerned about whether or not the amplified signal is actually the original signal – just amplified. The minuscule flow of electrons in a bus line may transport a signal, but this signal is not bound to that exact representation. We can send it through a transformer, optocoupler or piezo-transducer and, if we do it right, it just won’t matter. We are really ok if an amplified signal is a good, enlarged copy, as long as the copy retains the subset of properties of the original signal we are interested in.

Light is however indeed bound to its inherent representation as an electromagnetic wave. To understand how light is amplified – or copied – we need to look at the different properties of light both as a wave and as a particle. As a wave, it’s really not much more than synchronized oscillations of electric and magnetic fields propagating through space. To amplify it, we would want to somehow increase the amplitude of this oscillation while leaving its temporal course, such as its phase and frequency, intact. As a particle, however, a photon of a certain wavelength, direction, and polarization – all we can do is add more. So, if take this photon and we add another photon with this very same properties – a copy so to speak – we will see that the amplitude of our electromagnetic wave also doubles. It is amplified.

Since all we can do to amplify light, an optical amplifier must contain some kind of photon xerox — only this one really needs to leave the numbers intact. In lasers, this task of copying photons is done by special atoms (or molecules) inside the optical amplifier. They are called the active laser medium, and in a Helium-Neon laser, for example, it’s the Neon gas. All it needs is a container, an energy source, and some kind of windows for light to enter and exit. This contraption is the key element of every laser, from laser diodes over CO2 laser tubes to fiber lasers.

How To Make A Photon

Most photons we see in everyday life originate from a process called spontaneous emission. Atoms and molecules can be stimulated to transition to higher energy states than their ground state, in which the outer electrons leave their regular orbits and transition into more energetic states. If this state of excitation is long-lived (metastable), they may stay in this state for quite a while, but always keep a certain tendency to translate back to a lower energy state. Sooner or later, they will do so – spontaneously – while emitting a photon of a certain frequency in a random direction and with a random phase. This is called spontaneous emission, and the frequency of the emitted photon depends on the energy differential between the high (E2) and low energy state (E1). Compact fluorescent lamps, as well as incandescent lamps with a halogen filling, make use of this phenomenon.


How To Copy A Photon

Now, if a photon of this exact frequency f21, collides with such an excited atom, it can stimulate the atom to transition back to the low energy state right away, before it has time to do so spontaneously. The electromagnetic field of this original photon causes the atom to turn into an electrical dipole and oscillate with the external field. This deep interaction causes the emitted, new photon to take on the same phase and direction as the original one, which makes it practically a copy. Regarding most of the special properties of lasers, such as high monochromaticity, coherence and diffraction limited divergence angle, this quantum mechanical interaction is pretty much the bottom of the barrel.

However, inversely to stimulated emission, incoming photons can also run into atoms of the laser medium that are in the low-energy ground state. These photons will be absorbed, exciting the atom to the corresponding high-energy state. Unless another photon collides with the same atom soon enough to cause a stimulated emission, this atom is likely to spontaneously fall back to its ground state. It will still release a photon, but the photon released in a spontaneous emission can have any direction or phase and won’t align with the absorbed photon’s direction or phase, which results in an attenuation of incoming light.

Population Inversion

With a large number of atoms of the gain medium, the actual amplification process becomes a statistical sum of collisions. If there is a higher concentration of atoms in a low energy state than in the high energy state, we will experience a net loss of photons and thus, an attenuation of light. If the number of excited atoms is larger than the number of low energy atoms, we will experience a net gain. This overbalance of excited atoms is called the population inversion, and it is a basic requirement for optical amplification.

However, with an overbalance of excited atoms, such a two level system becomes highly unstable – it’s practically impossible to maintain. To achieve a population inversion in a stable system, optical amplifiers and lasers make use of more than two excitation levels of the involved atoms. For example, by exciting atoms from the ground state E1 to an excitation state E3, a population inversion between E3 and an intermediate energy state E2 can occur even if more low energy atoms are present in the ground state E1. As long as atoms transition from E2 to E1 – for example by a secondary spontaneous emission – at the same rate as atoms are lifted up from E1 to E3, the light amplification process at f32 can happen.

Pump it

To achieve the primary excitation of the laser medium to just the right high energy state, we need a mechanism to lift its atoms up there. This action is called pumping. Different types of lasers use different pumping methods, but besides keeping it going in an efficient and feasible way, it has little effect on the stimulated emission process itself. In some cases, the pumping itself is done by secondary light sources, such as discharge tubes or light emitting diodes. In other cases, the pumping is a well-designed bucket-chain of electrons and atoms or molecules passing on energy from a high voltage source to the atoms of the laser medium.

The first laser ever built, the ruby laser, uses photons emitted from a Xenon flash tube to excite chromium ions suspended in a synthetic sapphire. Other crystal lasers, such as Nd:YAG lasers, can be pumped by either arc lamps (or flashes), typically Xenon or Krypton, or more efficiently by light emitting diodes. Generally, diode pumped solid state lasers (DPSSL) use photons emitted from semiconductor diode junctions to pump various laser media.

CO2 lasers use electron collisions to induce a molecular oscillation in N2 molecules, which then pass on their energy and excite the CO2 laser medium. Helium-Neon lasers utilize electron collision to excite Helium atoms, which then collide with and excite the laser medium Neon. Except for CO2 lasers, which are still commonly used in laser cutters, the intricate pumping mechanisms that involve special gas mixtures and high voltages are more and more replaced by diode-based solid state alternatives.

The Optical Oscillator

While the optical amplifier may already be called a laser in a way, most optical amplifiers will not lase on their own. Any amount of photons that is going to be amplified while passing through the amplifier is bound to leave the amplifier very quickly — with light speed — and gone they are. On their way, they will not necessarily experience enough collisions with the atoms of the laser medium to achieve any reasonable lasing action. To make things worse, the optical amplifier amplifies light in all directions, which makes it a CFL tube at best. There are a few tricks to overcome this: One is, to give the optical amplifier a very, very long and narrow shape so that the only photons passing along this long axis of the amplifier will be amplified. Another way can be to increase the density of the gain medium. And eventually, mirrors can be installed on both ends of the optical amplifier to conveniently increase the effective length of the amplifier.


Because high-density gain mediums come with other challenges, such as high breakdown voltages for gaseous mediums, mirrors (and oftentimes long tubes) are the way to go here. Using mirrors, you can also create what is called an optical oscillator. Similar to a mass on a spring, an elastic string, or an LC-oscillator, they oscillate in resonance with a certain frequency. An optical oscillator is even easier to set up, since the main material you need is a chunk of space, with two mirrors on each end to prevent the light from exiting and getting absorbed. In this optical cavity, photons, light or electromagnetic waves (depending on how you look at it) can bounce back and forth between the two mirrors, superimposing to a standing wave.


You may have seen this before, it looks like a standing wave on a string. An optical oscillator behaves very similarly: The modes of this optical cavity are solely dependent on the propagation speed of the wave, in this case lightspeed, and the length of the cavity L. The modes — or resonance frequencies — that fit into our cavity depend mostly on the length of the cavity. If we choose the cavity to be long in comparison to the wavelengths we are interested in, in the hundreds of nanometers for visible light, the frequency response of this cavity shows many tightly and evenly spaced modes. If we choose the length of the cavity to be shorter, the spacing fs between the modes increases. This spacing is an important factor for the power output of industrial multimode lasers, which therefore typically have much longer cavities than for instance diode lasers in optical drives that rely on single frequency operation.


However, all oscillators are subject to losses, and we need to overcome them to keep any oscillation going. In lasers, this is done by — you may have guessed it — the optical amplifier. The optical amplifier goes right in between the mirrors, and if it’s strong enough to overcome the losses of your system, mostly the small amount of absorption in the mirrors, this system will oscillate.

This oscillation is called lasing, and it is really nothing more than electromagnetic waves bouncing back and forth between the mirrors, experiencing resonance from the cavity and recovering their losses when they pass through the amplifier. To make use of them, usually only one of the mirrors is highly reflective, typically 99.9 % or more. The other mirror, the output coupler, is partly transmissive and allows for a small amount, about 1%, of radiation to exit the cavity. Of course, the amplifier also has to compensate for this amount.

How The Laser Starts Lasing

Once we’ve put everything together, our optical cavity with the output coupler and the optical amplifier, we will want to turn it on. The pump medium will start elevating the laser medium to its high energy level, but there is no light inside the cavity to be amplified yet. Still, even with no incoming radiation, some of the excited atoms in the laser medium will randomly translate to a lower energy state, emitting a photon of just the right wavelength, but with random phase and into a random direction. We need only a few of them with the right phase to be directed along the axis of the optical cavity to get the avalanche going. These initial photons will bounce back and forth between the mirrors of the cavity, getting amplified each time, and the laser starts lasing.

Multimode Lasers

Optical cavities support all modes that fit in between the reflectors, so the exact number of wavelengths of light a laser produces depends mostly on the bandwidth of the optical amplifier. If its bandwidth is narrow, it may cover only a single mode of the optical cavity. If its bandwidth is large, multiple modes of the cavity can be amplified, and because this usually allows for a higher utilization of the pump mechanism, it naturally comes with a higher efficiency. Most industrial high power lasers actually don’t emit only a single frequency, but many. This is possible even though the gain medium operates at a very specific frequency defined by its excitation states, and comes by certain side effects depending on other characteristics of the gain medium. In gas mediums, the collisions of photons with atoms or molecules can shorten the decay time, which — following the statistics of these collisions — shapes the bandwidth of the amplifier to a bell curve. Also, Doppler effects due to the fast movement of gas atoms can further broaden the gain curve. There are many secondary imperfections in the various processes of pumping and stimulated emission that are used productively in multimode lasers.

Pulsed lasers

By pulsing a laser, a larger peak power output can be achieved than what continuous operation would make possible. This can, for example, be done electronically, or through a spark gap circuit, and with shorter pulses, higher peak power output values can be obtained. However, limitations in power output and pulse widths limit the usefulness of this approach.

Multimode lasers offer the possibility of achieving extremely short pulses at a very high momentary power output simply by combining the phase-locked modes of the optical cavity. By combining a series of equally spaced modes in the frequency domain, the interference of the modes causes the output to become a series of pulses in the time domain.


The phenomenon of beat, an acoustic interference of sound, where two tones of slightly off frequency create a perceived pulsation of the volume, is very similar. The more modes are superimposed, the shorter and more intense the pulse becomes, and in multimode lasers, they can be as short as a few femtoseconds (10-15 s) while producing several exawatts (1018 W) of peak power.


To achieve this, the modes of the optical cavity need to be tight enough spaced to fit as many as possible into the bandwidth of the optical amplifier. Also, the optical amplifier should have a large enough bandwidth to amplify more than a single frequency.

A Primer On Laser Optics

We still left out a few interesting features hidden in the internal optics of lasers, which are mostly the reflectors. First, the reflectors don’t need to be external, they can be evaporation deposited directly onto the polished windows of the optical cavity. Still, to make the output frequency of the laser tunable – which can be easily achieved by slightly changing the length of the cavity – it is practical to adjustably mount at least one of the mirrors externally. If one or both mirrors are mounted externally, some lasers will be equipped with Brewster windows, which is really just a window with its surface cut to a special angle.


This angle – the Brewster angle – is an angle where only light of a certain, linear polarization experiences can losslessly pass without reflections while all other polarizations are reflected away from the cavity and filtered from the beam. This minimizes reflections and polarizes the laser beam.

Also, the reflectors must not be plain. In some applications, it is advantageous to use concave or a mix of concave and plain or even convex reflectors. Now the beam exiting the output coupler is not parallel anymore, but can be converted into a parallel beam of any diameter by using simple optics.

I hope you enjoyed this very close look at the inner workings of lasers and optical amplifiers. There’s still a lot of engineering to get from here to just throwing a piece of plywood into a laser cutter, writing data in an optical drive, or exposing a photomask for silicon wafer production. Nevertheless, we have even seen impressive DIY builds of ruby lasers, CO2 lasers, and TEA lasers. DIY or industrial grade, they all share the same core principle, a quantum mechanical avalanche of cloned photons.

from Hack a Day

June 18, 2016

Vaadin Custom Layout Example

Filed under: Uncategorized — ketan @ 1:07 PM

In most GUI frameworks, a Layout manager is used to place widgets on the screen, there are multiple kind of layouts with different laying out policies. 1. The tools Java JDK 8 Latest Eclipse Mars Vaadin 7.6.6 Tomcat Server 8 2. Introduction The Vaadin custom layout uses HTML templates to lay out widgets on the …

from Java Code Geeks

June 14, 2016

Review: Monoprice MP Select Mini 3D Printer

Filed under: Uncategorized — ketan @ 5:54 PM

2016 is the year of the consumer 3D printer. Yes, the hype over 3D printing has died down since 2012. There were too many 3D printers at Maker Faire three years ago. Nevertheless, sales of 3D printers have never been stronger, the industry is growing, and the low-end machines are getting very, very good.

Printers are also getting cheap. At CES last January, Monoprice, the same company you buy Ethernet and HDMI cables from, introduced a line of 3D printers that would be released this year. While the $300 resin-based printer has been canned, Monoprice has released their MP Select Mini 3D printer for $200. This printer appeared on Monoprice late last month.

My curiosity was worth more than $200, so Hackaday readers get a review of the MP Select Mini 3D printer. The bottom line? There are some problems with this printer, but nothing that wouldn’t be found in printers that cost three times as much. This is a game-changing machine, and proof 2016 is the year of the entry-level consumer 3D printer.

Boring Specs

The standard Buddha from [kim]. This print exhibits Z banding, but that’s an issue with the slicer (Cura), and not the printer

The spec sheet for the MP Select Mini boasts a 120 x 120 x 120mm build area, 100 micron resolution, a heated build plate, and a printing speed of 55mm/second. Astonishingly, this printer lists Cura, Repetier-Host, ReplicatorG, and Simplify3D as the compatible software. This means that it speaks normal G-code.

Monoprice’s MP Select Mini doesn’t require special filament, and it can use the standard Open Source 3D printing software. This is in stark contrast to the XYZPrinting da Vinci from 2014. The da Vinci uses chipped, DRMed filament, and a proprietary interface instead of standard G-code. The MP Select Mini doesn’t pull any of these tricks, and is a minor miracle for a $200 printer.

Like most of the name brand printers found at CES last January, this printer is a rebadge of something already being made somewhere in China. The most likely suspect for a manufacture is a company called Infitary. You can buy a printer nearly identical to the Monoprice MP Mini on AliExpress right now, and it doesn’t seem Monoprice added anything special to this printer.

Judging by the spec sheet, I’d guess Monoprice doesn’t even know what they have on their hands here. The real specs for this printer are actually better than what Monoprice has published. This printer is capable of a layer height much smaller than 100 microns.


The first layer of Wade's Gear
The first layer of Wade’s Gear
The 3D Benchy. With this print, the printer demonstrated issues in cooling the filament and overhangs.
The 3D Benchy. With this print, the printer demonstrated issues in cooling the filament and overhangs.

Before showing off the prints the Monoprice MP Select Mini can produce, I must mention a simple fact: sample prints are not indicative of the quality of a printer. A 3D printer is just a CNC machine, and most of the work in turning an STL file into a real object is done by the slicer.

That said, there are a few things you can tell by looking at a few 3D print samples. Z axis wobble can be easily identified by looking at straight vertical walls. The ability of a printer to control the hotend temperature and use the fan can easily be seen in overhangs.

My first few prints were of Benchy, the tugboat 3D benchmarking tool. While not perfect, out of the box and with the recommended Cura settings, this printer produced a Benchy that is at least equal in quality from any other uncalibrated printer. With a little work in getting the right settings, I can see this printer producing Benchys that are at least equal to those produced by any other mid-range printer.

There is one glaring issue with the Monoprice MP Select Mini: the temperature control loop for the hotend is terrible. My printer has +/- 5 degree temperature swings over a period of several minutes, and this has been seen in other reviews of this model. The reason for this is an uncalibrated PID loop. Nearly every printer firmware has a PID autotune function that clears this problem right up. The firmware for this printer does not have a PID autotune function as far as I can tell.

Are the prints made on the MP Select Mini good? Yes, they can be. The MP Select Mini has a few problems, but none that won’t be easily fixed by the 3D printer community in a few months.


This printer is built down to a price. The strange thing is, this fact really doesn’t show until you start taking it apart. The chassis is all metal, the X and Y axes are belt driven on 6 mm rods, the Z axis is leadscrew driven, and there’s really not much to write home about. The printer is built solidly, and I can easily foresee it standing up to a lot of abuse.

The Motors and Mechanics

The standard for all 3D printers, from the cheapest fleaBay specials to the high-end Lulzbots and Ultimakers, is stepper motors. If you have a 3D printer, chances are you own four or five NEMA 17 stepper motors. Are they the best solution? That’s arguable, but it’s the standard. The MP Select Mini bucks this trend with a circular, non-NEMA motor on the Z axis.

The Z axis is leadscrew driven with an M4 threaded rod. It’s weird, and the Z axis is tremendously slow. This, however, is a selling point Monoprice failed to mention. Because the Z axis lead screw’s thread pitch is so fine, this printer can produce objects with a very, very small layer height. [Prusa]’s calculator gives a very low theoretical minimum layer height for this setup. The minimum layer height is not 100 micron as the spec sheet says, but it can be taken as evidence Monoprice is underselling the capabilities of this printer. It does mean Z axis travel is very slow, but that really doesn’t matter.

The Electronics

Here is where the MP Mini Select shines. If you’re looking for the one game-changing feature of this printer, it’s the controller board.

Before I broke out the hex wrenches for the teardown, my only impression of the firmware and electronics came from watching the test prints being built. There was something very different about this machine: the acceleration. The acceleration ramp when travelling from one end of the bed to another is like nothing else I’ve ever seen on a 3D printer. It was smooth, precise, and almost beautiful to watch. I figured this was custom firmware. It was, but that’s only half the story.

The electronics board for this printer is a 32-bit ARM Cortex M3, a vast improvement over the 8-bit ATmegas found in almost every other 3D printer controller.

The brains of the entire printer, an STM32F103 microcontroller. 32-bit 3D printers have finally arrived.
The brains of the entire printer, an STM32F103 microcontroller. 32-bit 3D printers have finally arrived.

This printer is an exercise in how inexpensively you can produce a printer, and these efforts clearly show in the electronics board. There are only six chips on this board: four HH4988 motor drivers (I assume off-brand clones of the popular A4988 stepper motor drivers), a buck converter (most likely for the LCD), and the microcontroller, an STM32F103 microcontroller. Yes, 32-bit printing is finally here.

It is impossible for me to understate the importance of the ARM microcontroller in this printer. Until now, with the exception of the Smoothieboard, the vast majority of 3D printers have been built around ATMega microcontrollers. This is understandable given the historical context; the first RepRaps were developed around 2009 or thereabouts, and the Arduino was very big at the time. 3D printer controller boards were developed around these 8-bit microcontrollers, and development continues to this day.

Everybody recognizes that ARM microcontrollers are the future of 3D printer control boards. ARM micros are cheaper – the STM32F103 on this printer board is half the price of the ‘standard’ ATMega2560 or AT90USB found in every other printer controller. ARM chips are more powerful, allowing for smoother acceleration. ARM micros are just a better solution to the problem.

Despite these obvious realities, thousands of people have been working on 8-bit controller boards for the better part of a decade. There’s a lot of technical debt to pay off in the Open Source 3D printing world. This technical debt was just paid off by a random embedded dev in China. If you want to see the future of 3D printer controller boards, all you need to do is buy a $200 printer from China.

As far as the LCD and controls go, they’re exactly what you would expect. It’s a full color TFT, most likely the same model used in an old non-smartphone, with a single rotary button. I believe the LCD and button assembly connect to the printer board over SPI. The controls allow the user to load a file from the SD card, move the axes around, and set the temperature. It’s the bare minimum, but you don’t really need much more.

Heated Bed

On most consumer 3D printers – those that have a heated bed, anyway – you’ll find a PCB heat bed screwed or clamped to an aluminum or glass plate. This is the standard. The MP Mini Select doesn’t have a separate build plate and PCB heater. Instead, a thin sheet of aluminum is bonded directly to a PCB heater.

While this makes for a much cheaper build – you don’t have to add an aluminum or glass sheet to the BOM, in addition to any fasteners – I am afraid it won’t be as robust as the standard separate aluminum/glass build plate and heater. That doesn’t mean it’s a bad solution, just that a bonded aluminum sheet won’t be able to take as much abuse without warping.

An innovative, low cost hotend

The theme of this printer is being built to a price, and nowhere is this more apparent than the hotend. To the manufacturer’s credit, this hotend does use a standard heater cartridge and replaceable thermistor. This is the future of hotends, and even though you can still buy hotends with nichrome heater cores, these are on their way out.

The hotend consists of a 0.4mm brass nozzle screwed into a heater block, and a heat break screwed onto an aluminum heatsink extrusion. This is possibly the simplest hotend in existence, but that doesn’t mean it’s skimping on features. I haven’t taken this hotend apart yet, but I suspect it is an all metal hotend. There’s simply no space in the heat break for a PTFE liner. That’s amazing for what is apparently the cheapest hotend you can buy and allows the MP Select Mini to print in exotic plastics.

I would not recommend printing in exotic plastics, though. There is one feature desperately missing from this hotend: a second fan to cool plastic squirting out of the nozzle. The MP Mini uses a single 20mm fan to blow air over both the hotend heat sink and right on to the molten plastic coming out of the nozzle. This is a bad design, and combined with the poor temperature control in the firmware, results in poor bridging capabilities for this printer.

These Are The Upgrades You’ll Want

Every 3D printer needs upgrades. Some, like the Lulzbot Taz 6, come with just about everything you could want, but ideally you’ll still want to stick a Raspberry Pi in there for headless, networked printing capabilities. Cheap eBay kits? You’ll want a better build plate, a new extruder, and maybe a better hotend. The MP Mini is fairly well equipped, but there are a few extras you’ll want.

A New Build Surface

As mentioned above, the one-piece heated bed for this printer is one of the most interesting designs I’ve ever seen. The print surface that comes with the MP Mini, though, is just a large sheet of masking tape. This will last you a few prints, but after that you’ll want something better.

For this review, I used a 6″ wide strip of Kapton and glue stick, but the current ‘best material for a build plate’ is a sheet of PEI or Ultem mounted to the build plate with a sheet of 3M 468MP adhesive transfer tape. You can get a 12″ x 12″ PEI sheet from Amazon for $16, and a 12″ x 12″ square of 468MP Transfer Tape for $17. That’s four PEI build surfaces for the MP Select for $37, and will be an amazing maintenance free build surface for PLA, ABS, and (reportedly) PET.

A Raspberry Pi / Octoprint Setup

There are reports the MP Mini is loud. Mine isn’t, but apparently results may vary. In any event, you’ll want to install your printer somewhere out of the way – a workshop, garage, or basement – and let it do its thing for several hours at a time.

While you can print from an SD card (and I have exclusively), that still means that you need to sneakernet files between a computer and the printer. Octoprint removes the need for this sneakernet, and allows for remote control of a printer over a network. If you plan on using this printer for more than just the occasional trinket, an Octoprint setup will be a huge benefit. The instructions are available on You’ll want the Raspberry Pi that has been gathering dust for several years, a USB WiFi adapter, SD card, and a USB power supply.

A Hotend Adapter

Print this thing. Print this thing now.
Print this thing. Print this thing now.

Every hotend will die. Hotends are consumables. They last a while, though, and even after 100 hours of printing, there’s nothing to tell me the hotend on the MP Mini won’t last as long as any other hotend.

Unfortunately, there’s no source for direct replacements. If you want to replace the hotend on this printer, you’ll have to shell out another $200 for a new printer. Spending $200 on a new hotend is crazy, and any company that forces that on consumers will quickly go out of business.

If you buy this printer, this should be the first thing you print. I whipped up an adapter in OpenSCAD that puts an E3D hotend on the MP Mini printer. It bolts directly onto the X carriage. Is it perfect? No, but if you print this adapter out, you’ll be able to print a better adapter out with your new hotend. Just print that and tape it to the back of your printer. You’ll thank me later.

Should You Buy This Printer?

There are problems with this printer. It is a closed source design, and replacement parts are impossible to find. The firmware doesn’t have handy features like Marlin’s autotuned PID values. The fan design for the hotend needs work. This printer uses a Bowden setup, so flexible filaments – Ninjaflex and Semiflex – are unusable. Trust me, I tried.

Printer Comparison

The Monoprice MP Select Mini is, by any account, a My First 3D Printer™, so let’s compare apples to apples. The class of printers that can be called a My First 3D Printer™ aren’t the Lulzbots, Ultimakers, or other machines that cost $1500 and up. ‘Beginner’ 3D printers are better defined by the SeeMeCNC Eris, the Printrbot Play and Metal Simple, the Deezmaker Bukito, the Maker’s Toolworks MiniMax, the da Vinci printer, and [Prusa]’s i3 Mk2.

The Monoprice MP Select Mini stands out in its price range. This machine is only $200, and you’re getting features you won’t find in a $600 Printrbot. This is a game-changing machine, and I would recommend this to anyone looking for their first 3D printer. Thanks to Monoprice, the entire market for entry-level consumer 3D printers has been upended. $200 is almost impulse purchase territory, and Monoprice is going to sell a lot of these machines.

Now we have some work to do

When the da Vinci printer was released two years ago, an immense amount of effort went into reverse engineering the chipped filament and reprogramming the control board to speak normal G-code. Now the same work must be done on this printer.

The control board for this printer must be reverse engineered and duplicated. The first person to do that will lay the foundation for the next generation of RepRap control electronics. I would highly recommend putting the reverse engineering efforts on Perhaps more importantly, a proper, Open Source 3D printer firmware must be ported to this printer. Right now, many of the shortcomings of this printer can be fixed through a firmware update. With open, improvable firmware, combined with its decent hardware, it could be outstanding.

Even without a rewrite of the Marlin firmware and a clone of this electronics board, it’s still a fantastic printer. It’s not perfect, but it’s good enough for the thousands of people who will end up with one of these on their workbenches.

from Hack a Day

June 12, 2016

Arduino VU Meter with LED strips

Filed under: Uncategorized — ketan @ 5:54 PM

Thanks to Nicolas for sharing this project with us!

I have always wanted some kind of LED VU-Meter because I like music and LEDs but all of the devices I found online had an integrated microphone or used a lot of pins (so a shift register was required), and I didn’t want that. I wanted to display on the VU-Meter only the music played on my PC, so I needed a PC-based solution. And this is it.

Read more.

from Adafruit Blog

June 9, 2016

Thank you for watching dotnetConf 2016!

Filed under: Uncategorized — ketan @ 11:03 PM


dotnetConf 2016 is a wrap! Thank you to all who tuned in live on Channel 9, asked questions, and participated in our twitter feed. We had a lot of awesome sessions from various product teams and community experts that showed us all sorts of cool things we can build with .NET across platforms and devices. There’s never been a better time to be a .NET developer!

Watch all the sessions on demand on Channel 9.

Here’s a recap of the big announcements we made:

And here’s the list of sessions so you can jump right in!

Attend a dotnetConf.local event

But wait, it doesn’t end here! Why sit in front of your computer all day when you can get out for an in-person .NET meetup?! We’re partnering with .NET meetups around the world to bring you .NET content from dotnetConf in person to a city near you. We’re calling it dotnetConf.local. We’re reaching out to .NET user group leaders who have scheduled .NET presentations June through September on the topics presented here at dotnetConf and offer to fund your meals. Not pizza! :-) Check the website often for a list of participating meetups near you. We’ll keep updating the site as more come on board.


from .NET Blog

June 6, 2016

Presentation: Netflix Keystone – How We Built a 700B/day Stream Processing Cloud Platform in a Year

Filed under: Uncategorized — ketan @ 9:25 PM

Peter Bakas presents in detail how Netflix has used Kafka, Samza, Docker, and Linux to implement a multi-tenant pipeline processing 700B events/day in the Amazon AWS cloud.

By Peter Bakas

from InfoQ

Comparison of Event Sourcing with Stream Processing

Filed under: Uncategorized — ketan @ 9:24 PM

Event sourcing and CQRS are two patterns that has emerged in the Domain-Driven Design (DDD) community. Stream processing builds on similar ideas but has emerged in a different community, Martin Kleppmann noted in his presentation at the Domain-Driven Design Europe conference earlier this year comparing event sourcing with stream processing.

By Jan Stenberg

from InfoQ

Article: Exercises for Building Better Teams

Filed under: Uncategorized — ketan @ 9:23 PM

Have you ever seen a team perform so great that you wanted to join it? If you examine the values of such a team, you may discover a perfect balance of orientation on people and results. If you are trying to discover how far away your own team is from this state, read this article and try the exercises to find your own state of perfection.

By Justyna Wykowska

from InfoQ

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