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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EMMC Hacks For The Speed And Capacity Upgrade Win

You could say that it is the essence of a site like this one, that the kind of people who form our readership are also the kind of people who examine the specs of the devices in front of them to reveal hidden features. Such was the case with [Ryan], who noticed that the eMMC controller on his 96Boards HiKey development board supports both HS200 data transfer speeds and 1.8v signaling, both of which it wasn’t using.

In unlocking the extra performance, he takes readers through a primer on the device tree, and is happy to report that his transfer rate has increased from 26 to 36 MB/s, a tidy return on his work.

However, the story doesn’t end there. The 8GB Samsung eMMC chip wasn’t quite as roomy as he’d have liked, so it was time to replace it with a 32GB version. Even with careful desoldering, he managed to lift a few pads, though very fortunately they were ones that were either NC or power rails that were duplicated elsewhere. Some tricky reflowing of what is quite a formidable BGA package to do by hand, and he was rewarded with a working board featuring higher flash capacity. We salute him for taking it on, we probably wouldn’t have had the courage.

We’ve brought you a similar upgrade before, this time an eMMC on a Nexus 5 phone.

Thanks [darkspr1te] for the tip.

The Science Behind Lithium Cell Characteristics and Safety

To describe the constraints on developing consumer battery technology as ‘challenging’ is an enormous understatement. The ideal rechargeable battery has conflicting properties – it has to store large amounts of energy, safely release or absorb large amounts of it on demand, and must be unable to release that energy upon failure. It also has to be cheap, nontoxic, lightweight, and scalable.

As a result, consumer battery technologies represent a compromise between competing goals. Modern rechargeable lithium batteries are no exception, although overall they are a marvel of engineering. Mobile technology would not be anywhere near as good as it is today without them. We’re not saying you cannot have cellphones based on lead-acid batteries (in fact the Motorola 2600 ‘Bag Phone’ was one), but you had better have large pockets. Also a stout belt or… some type of harness? It turns out lead is heavy.

The Motorola 2600 ‘bag phone’, with a lead-acid battery. Image CC-BY-SA 3.0 source: Trent021

Rechargeable lithium cells have evolved tremendously over the years since their commercial release in 1991. Early on in their development, small grains plated with lithium metal were used, which had several disadvantages including loss of cell capacity over time, internal short circuits, and fairly high levels of heat generation. To solve these problems, there were two main approaches: the use of polymer electrolytes, and the use of graphite electrodes to contain the lithium ions rather than use lithium metal. From these two approaches, lithium-ion (Li-ion) and lithium-polymer (Li-Po) cells were developed (Vincent, 2009, p. 163). Since then, many different chemistries have been developed.

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How To Select Just About Any Electronic Part

Sometimes you see an excellent post somewhere else on the web, and then discover that it is one of a series of similarly good posts that you completely missed when they were published. If you are a Hackaday scribe you are left wondering how you managed to pass them by, and then why on earth you didn’t think of writing them yourself.

Such is the case with [Sanket Gupta]’s excellent series for Octopart, of posts titled “How to select a…” and then a class of component. It was the latest, “How to select a voltage regulator” that caught our eye first, but then we found the previous installments dealing with capacitors, resistors, inductors, connectors, IC packages and MCUs. Each one provides a basic primer for the engineer, in terms of both parts selection based on capability and on suitability for manufacturing, and while you may think that only an inexperienced reader might find benefit in such pieces the reality is that everybody can learn something.

So if you are involved in choosing electronic parts, no matter at what level, take a look at this series. If you know everything [Sanket] has to say then we congratulate you on your mastery of the field, however we think most readers will find them to be an interesting and useful resource.

Header image: Kae [Public domain].