# Why Is My 470uF Electrolytic Cap More Like 20uF?

Inductors are more like a resistor in series with an ideal inductor, resistors can be inductors as well, and well, capacitors aren’t just simply a capacitance in a package. Little with electronics is as plain and simple in reality as basic theory would have you believe. [Tahmid Mahbub] was measuring an electrolytic capacitor with an LCR and noticed it measuring 19 uF despite the device being rated at 470 uF. This was because such parts are usually specified at low frequencies, and at a mere 100 kHz, it was measuring way out of the specification they were expecting. [Tahmid] goes into a fair bit of detail regarding how to model the equivalent circuit of a typical electrolytic capacitor and how to determine with a bit more accuracy what to expect.

The basic equivalent circuit for a capacitor has a series resistance and inductance, which covers the connecting leads and any internal tabs on the plates. A large-valued parallel resistor models the leakage through the dielectric in series with the ideal capacitance, which is responsible for the capacitor’s self-discharge property. However, this model is still too simple for some use cases. A more interesting model, shown to the left, comprises a ladder of distributed capacitances and associated resistances that result in a progressively longer time-constant component as you move from C1 to C5. This resembles more closely the linear structure of the capacitor, with its rolled-up construction. This model is hard to use in any practical sense due to the need to determine values for the components from a physical part. Still, it is useful to understand why such capacitors perform far worse than you would expect from just a simple equivalent model that looks at the connecting leads and little else.

We normally chuckle at high-profile auctions where people compete to pay as much as possible for items they clearly don’t need. It’s easy to laugh when the items on the block are things like paint-spattered canvases, but every once in a while some genuine bit of history that really piques our interest goes on sale. Such is the case with what is claimed to be an original Steve Wozniak-built Blue Box, going on sale November 5. The prospectus has an excellent summary of the history of the “Two Steves” and their early business venture making and selling these devices to Berkeley students eager to make free long distance phone calls. The item on sale is a very early rev, most likely assembled by Woz himself. The current owner claims to have bought it from Woz himself in the summer of 1972 while on a roadtrip from Sunnyvale to Los Angeles. Estimated to go for \$4,000 to \$6,000, we really hope this ends up in a museum somewhere — while we’ve seen attempts to recreate Woz’s Blue Box on Hackaday.io, letting a museum study an original would be a great glimpse into our shared technological history.

Not in the market for old tech? No problem — Digilent wants to get rid of 3,000 PCBs, and quickly. They posted the unusual offer on reddit a couple of days ago; it seems they have a huge stock of populated boards for a product that didn’t quite take the market by storm. Their intention is likely not to flood the market with scopes cobbled together from these boards, but rather to make them available to someone doing some kind of art installation or for educational purposes. It’s a nice gesture, and a decent attempt to keep these out of the e-waste stream, so check it out if you have a need.

Speaking of PCBs, SparkFun has just launched an interesting new service: SparkFun À La Carte. The idea is to make it really easy to design and build prototype boards. Instead of using traditional EDA software, users select different blocks from a menu. Select your processor, add components like displays and sensors, and figure out how you want to power it, and SparkFun will do the rest, delivering a fully assembled board in a few weeks. It certainly stands to suck the fun out of the design process while also hoovering up your pocketbook: “A \$949 design fee will be applied to all initial orders of a design”. You can get your hands on the design files, but that comes with an extra fee: “they can be purchased separately for \$150 by filling out this form”. But for someone who just needs to hammer out a quick design and get on with the next job, this could be a valuable tool.

Another day, another IoT ghost: Reciva Radio is shutting down its internet radio service. A large banner at the top of the page warns that the “website will be withdrawn” on January 31, 2021, but functionality on the site already appears limited. Users of the service are also reporting that their Reciva-compatible radios are refusing to stream content, apparently because they can’t download anything from the service’s back end. This probably doesn’t have a huge impact — I’d never heard of Reciva before — but it makes me look at the Squeezebox radio we’ve got in the kitchen and wonder how long for the world that thing is. It’s not all bad news, though — owners of the bricked radios will now have a great opportunity to hack them back into usefulness.

By the time this article is published, Halloween will be history and the hordes of cosplaying candy-grubbers who served as welcome if ironic respite from this non-stop horror show of a year will be gone. Luckily, though, if it should come to pass that the dead rise from their graves — it’s still 2020, after all — we’ll know exactly how to defeat them with this zombie invasion calculator. You may remember that last year Dominik Czernia did something similar, albeit with vampires. Switching things up from the hemophagic to the cerebrophagic this year, his calculator lets you model different parameters, like undead conversion percentage, zombie demographics, and attack speed. You’ve also got tools for modeling the response of the living to the outbreak, to see how best to fight back. Spoiler alert: everyone will need to bring Tallahassee-level badassery if we’re going to get through this.

# Analog Discovery 2 As A Vector Network Analyzer

A while back, I posted a review of the Analog Discovery 2, which is one of those USB “do everything” instruments. You might recall I generally liked it, although I wasn’t crazy about the price and the fact that the BNC connectors were an extra item. However, in that same post, I mentioned I’d look at the device’s capabilities as a network analyzer (NA) sometime in the future. The future, as they say, is now.

## What’s an NA?

In its simplest form, there’s not much to an NA. You sweep a frequency generator across some range of frequencies. You feed that into some component or network of components and then you measure the power you get out compared to the power you put in. Fancy instruments can do some other measurements, but that’s really the heart of it.

The output is usually in two parts. You see a scope-like graph that has the frequency as the X-axis and some sort of magnitude as the Y-axis. Often the magnitude will be the ratio of the output power to the input power as a decibel. In addition, another scope-like output will show the phase shift through the network (Y-axis) vs frequency (X-axis). The Discovery 2 has these outputs and you can add custom displays, too.

Why do you care? An NA can help you understand tuned circuits, antennas, or anything else that has a frequency response, even an active filter or the feedback network of an oscillator. Could you do the same measurements manually? Of course you could. But taking hundreds of measurements per octave would be tedious and error-prone.

# Review: Digilent Analog Discovery 2

I recently opened the mailbox to find a little device about the size of White Castle burger. It was an “Analog Discovery 2” from Digilent. It is hard to categorize exactly what it is. On the face of it, it is a USB scope and logic analyzer. But it is also a waveform generator, a DC power supply, a pattern generator, and a network analyzer.

I’ve looked at devices like this before. Some are better than others, but usually all the pieces don’t work well at the same time. That is, you can use the scope or you can use the signal generator. The ones based on microcontrollers often get worse as you add channels even. The Analog Discovery 2 is built around an FPGA which, if done right, should get around many of the problems associated with other small instrumentation devices.

I’d read good things about the Discovery 2, so I was anxious to put it through its paces. I will say it is an impressive piece of gear. There are a few things that I was less happy with, though, and I’ll try to give you a fair read on what I found both good and bad.

# HDCP Falls To FPGA-based Man-in-the-middle Attack

It’s been a little while since we talked about HDCP around here, but recent developments in the area of digital content protection are proving very interesting.

You might remember that the Master Key for HDCP encryption was leaked last year, just a short while after Intel said that the protection had been cracked. While Intel admitted that HDCP had been broken, they shrugged off any suggestions that the information could be used to intercept HDCP data streams since they claimed a purpose-built processor would be required to do so. Citing that the process of creating such a component would be extremely cost-prohibitive, Intel hoped to quash interest in the subject, but things didn’t work out quite how they planned.

It seems that researchers in Germany have devised a way to build such a processor on an extremely reasonable budget. To achieve HDCP decryption on the fly, the researchers used a standard off the shelf Digilent Atlys Spartan-6 FPGA development board, which comes complete with HDMI input/output ports for easy access to the video stream in question. While not as cheap as this HDCP workaround we covered a few years ago, their solution should prove to be far more flexible than hard wiring an HDMI cable to your television’s mainboard.

The team claims that while their man-in-the-middle attack is effective and undetectable, it will be of little practical use to pirates. While we are aware that HDMI data streams generate a ton of data, this sort of talking in absolutes makes us laugh, as it often seems to backfire in the long run.

[via Tom’s Hardware]

# ChipKIT Temperature Shield Supports A Dozen Sensors

[Will] wrote in to share a useful add-on he designed for the ChipKIT UNO 32, a 12-port temperature sensor board.

Constructed for one of his customers, the shield accepts any 2-wire 10k thermistor sensors, outputting the readings to a small LCD screen. The screen is supported by some code put together by his associate [crenn], but you are not limited to solely displaying the temperatures there. Since this module piggybacks on top of the ChipKIT the same fashion as any standard shield, you clearly have the ability to use and manipulate the data at will. With 12 ports on board this would work well for a house-wide temperature monitoring system, or perhaps in a complex brewing setup.

Both the temperature shield and LCD boards have been released under the Open Source Hardware License, so you can easily build your own if you have the means, though [Will] has a few extras he’s willing to sell if you need one quickly.