New Part Day: A fake Sun

LED technology has improved by leaps and bounds in recent years, with what was once considered unachievable being common place now. Two of the main parameters of interest, total input power and conversion efficiency have been steadily increasing over the years. An efficacy of 120 lumens/watt is fairly common nowadays, and it may not be improbable to expect double this figure in the near future. Input power ratings have also steadily increased, with single LED units capable of 100 W or more becoming common.

But the Chinese manufacturer Yuji seems to have hit the ball out of the park by introducing their BC-Series, 500 W, high CRI, high Power, COB LED. Single, 500 W COB LED’s are not new and have been available since a couple of years, but their emitting surface areas are quite large. For example, a typical eBay search throws up parts such as this one – 500 W, high Power LED, 60,000 lm, 6000-6500K. It has a large, square emitting area of 47.6 x 47.6 mm. By comparison, the Yuji BC-Series are 27 mm square, with an active emitting area only 19 mm in diameter. This small emitting area makes it easier to design efficient reflector and/or lens units for the LED.

Luminous Flux is between 18,000 to 21,000 for a color temperature of 3200 K, and between 20,000 to 24,000 for the 5600 K type. Further, this high power rating is accompanied with a pretty high color rendering index (CRI) above 95. This allows the LED to faithfully reveal the natural colors of objects due to its wide spectrum. Electrically, it is rated for 12 Amps with input voltage between 35 V to 39 V. This translates to between 420 W ~ 468 W of input electrical power. Some quick math tells us that the efficacy efficiency works out to just a little over 50 lm/W, which isn’t all that great. But with light sources, you can have high-efficacy high-efficiency or high CRI, but not both – that’s just how the physics of it works.

At US $ 500 a pop, these eye blinders do not come cheap and may not find much use for individual hackers. But for some applications, such as studio and theatre lighting or photography, they may be just what the Doctor prescribed. In the video after the break, you can see [Matt] from DIY Perks give a rundown of the LED’s features and take it for a test ride.

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A Sandbox for DIY Pinball Design

If you’ve always wanted to build your own pinball machine but have no idea where to start, this is the project for you. [Chris] is in the process of building a 3/4 size pinball table and is currently in the waiting-for-parts stage. As they arrive, he is testing them in a sandbox he built in an afternoon. Let [Chris]’s proving ground be your quick-start guide to all the ways you could approach the two most important parts of any pin: the flippers and targets.

The field of play is a sturdy piece of particle board, and the cardboard walls are attached with hot glue. [Chris] designed and printed a pair of flippers that are driven by some cheap remote door lock motors he found at a popular online auction house. You can see how snappy are in the test video after the break.

We love the crisp action and elegant simplicity of the spring-loaded drop targets [Chris] designed. Right now he resets them manually, but soon they will be reset by a solenoid or maybe a motor. We can’t wait to see how the table turns out. In the meantime, we’ll have to go back to drooling over this amazing life-size 3D-printed pinball machine.

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Heavily Hacked Printer for DIY PCBs

Sometimes we get tips that only leave us guessing as to how — and sometimes why — a project was built. Such is the case with this PCB printer; in this case, the build specifics are the only thing in question, because it puts out some pretty impressive PCBs.

All we have to go on is the video after the break, which despite an exhaustive minutes-long search appears to be the only documentation [Androkavo] did for this build. The captions tell us that the printer is built around the guts from an Epson Stylus Photo 1390 printer. There’s no evidence of that from the outside, as every bit of the printer has been built into a custom enclosure. The paper handling gear has been replaced by an A3-sized heated flatbed, adjustable in the Z-axis to accommodate varying board thicknesses. The bed runs on linear rails that appear custom-made. Under the hood, the ink cartridges have been replaced with outboard ink bottles in any color you want as long as it’s black. The video shows some test prints down to 0.1 mm traces with 0.1 mm pitch — those were a little dodgy, but at a 0.2 mm pitch, the finest traces came out great. The boards were etched in the usual way with great results; we wonder if the printer could be modified to print resist and silkscreens too.

[Androkavo] seems to have quite a few interesting projects in his YouTube channel, one of which — this wooden digital clock — we featured recently. We’d love to learn more about this printer build, though. Hopefully [Androkavo] will see this and comment below.

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Active Discussion About Passive Components

People talk about active and passive components like they are two distinct classes of electronic parts. When sourcing components on a BOM, you have the passives, which are the little things that are cheaper than a dime a dozen, and then the rest that make up the bulk of the cost. Diodes and transistors definitely fall into the cheap little things category, but aren’t necessarily passive components, so what IS the difference?

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Radio Tuning The Quicksilver Way

Modern radios are often digital affairs, in which the frequency is derived from a stable crystal oscillator and varied through a microprocessor controlled frequency synthesiser. It won’t drift, and it’s exactly on the frequency dialed in. Older radios though relied on a tuned circuit, a combination of capacitor and inductor, for their frequency selection. If you were curious enough to peer inside — and we know you were — you’d have seen the moving vanes of a variable capacitor controlled by the tuning knob.

Of course, there is another way to adjust a tuned circuit: by changing the value of the inductor. Older car radios for instance moved a ferrite slug inside a coil to tune from station to station. But that method is not good enough for [David Mills]. Being in possession of some finely graduated syringes he decided to try liquid tuning by increasing the volume within the coil.

Solutions of salts made little difference, so he reached for some mercury. The result is an RF inductor wound round a syringe body, with a body of mercury whose position can be adjusted by the plunger. He measures the Q factor of the coil with air core or mercury core, and as the inductance decreases with more mercury, so does the Q.

We see home-made parts from time to time, and there’s nothing too special about permeability tuning. However, this unusual take on the matter makes this one rather special. We doubt we’ll see its like very often in the future.

An Introduction to Solid State Relays

When we think of relays, we tend to think of those big mechanical things that make a satisfying ‘click’ when activated. As nice as they are for relay-based computers, there are times when you don’t want to deal with noise or the unreliability of moving parts. This is where solid-state relays (SSRs) are worth considering. They switch faster, silently, without bouncing or arcing, last longer, and don’t contain a big inductor.

Source Fotek SSR Specifications Sheet

An SSR consists of two or three standard components packed into a module (you can even build one yourself). The first component is an optocoupler which isolates your control circuit from the mains power that you are controlling. Second, a triac, silicon controlled rectifier, or MOSFET that switches the mains power using the output from the optocoupler. Finally, there is usually (but not always) a ‘zero-crossing detection circuit’. This causes the relay to wait until the current it is controlling reaches zero before shutting off. Most SSRs will similarly wait until the mains voltage crosses zero volts before switching on.

If a mechanical relay turns on or off near the peak voltage when supplying AC, there is a sudden drop or rise in current. If you have an inductive load such as an electric motor, this can cause a large transient voltage spike when you turn off the relay, as the magnetic field surrounding the inductive load collapses. Switching a relay during a peak in the mains voltage also causes an electric arc between the relay terminals, wearing them down and contributing to the mechanical failure of the relay.

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The Electronics Markets of Ho Chi Minh City, Vietnam

When we think about world-famous electronics markets in Asia, usually Shenzhen, Tokyo’s Akihabara, or Shanghai’s Beijing Road come to mind.

There’s another market that I’ve had my eye on for a few years: Nhật Tảo market in Ho Chi Minh City, Vietnam. It might not be as large or accessible as the more well-known markets, but it’s very much worth a visit if you’re in the area. I decided it was time to hop on my red motorbike (red things go faster) and give you a short tour of the central market, as well as some more hobbyist-friendly options.

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