Taking A Capacitor Microphone To The Next Level

February 24, 2021 by Jenny List 13 Comments

There was a time when a microphone for most people was a cheap plastic affair that probably came for free with their sound card, but in the age of pandemic video streaming no desktop is complete without a chunky model that looks for all the world as though it escaped from a studio. Few people make their own microphones, so the work of [DJJules] in building very high quality condenser microphones is a particularly fascinating read.

A condenser microphone is a capacitor in which one plate is formed by a conductive diaphragm. A bias voltage is supplied to the diaphragm via a resistor, and since the charge on the plate remains constant as its capacitance changes with the sound vibrations, the voltage on the capacitor changes accordingly. This is picked up by a high impedance buffer and from there fed to a normal microphone input. This Instructable uses a commercial condenser microphone capsule, and takes the reader through generating the bias voltage for it before describing the op-amp buffer circuit.

The most interesting part comes at the end, as we’re shown how the sensitivity pattern of a dual-microphone array can be tuned to be omnidirectional, cardoid, or figure-of-eight. This is probably the norm among audio engineers, but we rarely see this sort of insight in our community. We may never build a microphone of our own, but it’s fascinating to see this one from the ground up in the video below the break.

If you’re confused about the difference between a condenser microphone and the more common electret condenser microphone, we have published a guide to that topic. Continue reading “Taking A Capacitor Microphone To The Next Level” →

An Op-Amp From The Ground Up

January 30, 2021 by Jenny List 49 Comments

If we had to pick one part to crown as the universal component in the world of analogue electronics, it would have to be the operational amplifier. The humble op-amp can be configured into so many circuit building blocks that it has become an indispensable tool for designers. It’s tempting to treat an op-amp as a triangular black box in a circuit diagram, but understanding its operation gives an insight into analogue electronics that’s worth having. [Mitsuru Yamada]’s homemade op-amp using discrete components is thus a project of interest, implementing as it does a complete simple op-amp with five transistors.

Looking at the circuit diagram it follows the classic op-amp with a long-tailed pair of NPN transistors driving a PNP gain stage and finally a complimentary emitter follower as an output buffer. It incorporates the feedback capacitor that would have been an external component on early op-amp chips, and it has a couple of variable resistors to adjust the bias. Keen eyed readers will notice its flaws such as inevitably mismatched transistors and the lack of a current mirror in the long-tailed pair, but using those to find fault in a circuit built for learning is beside the point. He demonstrated it in use, and even goes as far as to show it running an audio power amplifier driving a small speaker.

For the dedicated student of op-amps, may we suggest further reading as we examine the first integrated circuit op-amp?

A Look At The Interesting RP2040 Peripheral, Those PIOs

January 29, 2021 by Jenny List 41 Comments

The Raspberry Pi Pico is the latest product in the Raspberry Pi range, and it marks a departure from their previous small Linux-capable boards. The little microcontroller board will surely do well in the Pi Foundation’s core markets, but its RP2040 chip must have something special as a commercial component to avoid being simply another take on an ARM microcontroller that happens to be a bit more expensive and from an unproven manufacturer in the world of chips. Perhaps that special something comes in its on-board Programable IO perhipherals, or PIOs. [CNX Software] have taken an in-depth look at them, which makes for interesting reading.

Continue reading “A Look At The Interesting RP2040 Peripheral, Those PIOs” →

Chasing Down Bad Caps To Save A Troubled PSU

January 26, 2021 by Tom Nardi 36 Comments

We know what you’re thinking. It’s a bad power supply, of course it was capacitors to blame. But even if we all intuitively know at this point that bad caps are almost always the culprit when a PSU gives up the ghost, it’s not always easy to figure out which one is to blame. Which is why this deep dive into a failed ETK450AWT by [eigma] is worth a look.

The first sign of trouble was when the computer would unexpectedly reboot with nothing in the system logs to indicate a problem. Eventually, [eigma] noticed a restart before the operating system even loaded, which confirmed the hardware was to blame. A quick look at the PSU output with a voltmeter showed things weren’t too far out of spec, but putting an oscilloscope on the 12 V line uncovered a nasty waveform that demanded further investigation.

By carefully following traces and comparing with common PSU diagrams, [eigma] was able to identify the SG5616 IC that checks the various voltages being produced by the PSU and generates the PWR_OK signal which tells the motherboard that everything is working normally. As before, all of the DC voltages at this chip seemed reasonable enough, but the pin that was measuring AC voltage from the transformer was showing the same ripple visible on the 12 VDC line.

Even more digging uncovered that the transformer itself had a control IC nestled away. The 13 VDC required by this chip to operate is pulled off the standby transformer by way of a Zener diode and a couple capacitors, but as [eigma] soon found, the circuit was producing another nasty ripple. Throwing a few new capacitors into the mix smoothed things out and got the PSU to kick on, but that’s not quite the end of the story.

Pulling the capacitors from the board and checking their values with the meter, [eigma] found they too appeared to be within reasonable enough limits. They even looked in good shape physically. But with the help of a signal generator, he was able to determine their equivalent series resistance (ESR) was way too high. Case closed.

While swapping out blown capacitors in older electronics is something of a rite of passage for hardware hackers, this case is an excellent example of how even the simplest of fixes can be tricky to troubleshoot.

ESP32 Inkplate Gives Kindle Displays A Second Chance

January 22, 2021 by Tom Nardi 17 Comments

Over the years, we’ve seen plenty of hackers repurpose their Kindle or similar e-reader to reap the benefits of its electronic paper display. Usually this takes the form of some software running on the reader itself, since cracking the firmware is a lot easier than pulling out the panel and figuring out how to operate it independently. But what if somebody had already done that hard work for you?

Enter the Inkplate. By pairing a recycled Kindle display with an ESP32, Croatian electronics company e-radionica says they’ve not only created an open hardware e-paper display that’s easy for hackers and makers to use, but keeps electronic waste out of the landfill. Last year the $99 USD 6 inch version of the Inkplate ended its CrowdSupply campaign at over 920% of its original goal. The new 9.7 inch model is priced at $129, and so far managed to blow past its own funding goal just hours after the campaign went live. Clearly, the demand is there.

The new model’s e-paper display isn’t just larger, it also features a higher 1200 x 825 resolution and reduced refresh time. Outside of the screen improvements, you’ll also find more GPIO pins, an RTC module to keep more accurate time, and a USB Type-C port for both programming and power. You also get a choice of languages to use, with both Arduino and MicroPython libraries available for interfacing with the display. Interestingly, the Inkplate also features a so-called “Peripheral Mode” that allows you to draw graphics primitives on the screen using commands sent over UART.

While we’ve recently seen some very promising efforts to repurpose old e-paper displays, the turn-key solution offered by the Inkplate is admittedly very compelling. If you’re looking for an easy way to jump on the electronic paper bandwagon that works out of the box, this might be your chance.

[Thanks to Krunoslav for the tip.]

Raspberry Pi Enters Microcontroller Game With $4 Pico

January 20, 2021 by Elliot Williams 351 Comments

Raspberry Pi was synonymous with single-board Linux computers. No longer. The $4 Raspberry Pi Pico board is their attempt to break into the crowded microcontroller module market.

The microcontroller in question, the RP2040, is also Raspberry Pi’s first foray into custom silicon, and it’s got a dual-core Cortex M0+ with luxurious amounts of SRAM and some very interesting custom I/O peripheral hardware that will likely mean that you never have to bit-bang again. But a bare microcontroller is no fun without a dev board, and the Raspberry Pi Pico adds 2 MB of flash, USB connectivity, and nice power management.

As with the Raspberry Pi Linux machines, the emphasis is on getting you up and running quickly, and there is copious documentation: from “Getting Started” type guides for both the C/C++ and MicroPython SDKs with code examples, to serious datasheets for the Pico and the RP2040 itself, to hardware design notes and KiCAD breakout boards, and even the contents of the on-board Boot ROM. The Pico seems designed to make a friendly introduction to microcontrollers using MicroPython, but there’s enough guidance available for you to go as deep down the rabbit hole as you’d like.

Our quick take: the RP2040 is a very well thought-out microcontroller, with myriad nice design touches throughout, enough power to get most jobs done, and an innovative and very hacker-friendly software-defined hardware I/O peripheral. It’s backed by good documentation and many working examples, and at the end of the day it runs a pair of familiar ARM MO+ CPU cores. If this hits the shelves at the proposed $4 price, we can see it becoming the go-to board for many projects that don’t require wireless connectivity.

But you want more detail, right? Read on.

Continue reading “Raspberry Pi Enters Microcontroller Game With $4 Pico” →

Custom Coil Lets Mouse Charge Without Wires

January 13, 2021 by Tom Nardi 22 Comments

It’s 2021, shouldn’t all of our devices be able to pull the power they need from the ether? [Sasa Karanovic] certainly thinks so, which is why he recently took it upon himself to add wireless charging capabilities to his desktop computer peripherals. The Qi transmitter and receiver modules are relatively cheap and easy to come by, the trick is in getting them installed.

The keyboard gets non-invasive Qi charging.

For the keyboard, [Sasa] took the path of least resistance. The receiver coil lives inside a little 3D printed box attached to the back, and power is routed through a hacked up right-angle USB cable. It’s a simple addition that doesn’t make any permanent changes to the keyboard; perfect for those who don’t want to risk toasting their gear.

But that wasn’t really an option for the mouse. Obviously the Qi hardware would have to go on the inside, but at a glance it was clear there wasn’t enough room to mount the stock coil. So [Sasa] pulled the original coil apart and rewound it around a small 3D printed jig. This resulting coil was perfectly sized to fit inside the flat area on the left side of the mouse with no apparent degradation in charging ability. Wiring the module up to an unpopulated pad on the PCB allowed him to easily inject the 5 V output into the device’s existing charging circuitry.

We’ve seen plenty of aftermarket Qi charging coils take up permanent residence in various gadgets, but rewinding the coil is a neat trick that we’ve only seen pulled off a couple times in the past. Something to file away mentally should you ever want to wirelessly power up one of your projects.

Continue reading “Custom Coil Lets Mouse Charge Without Wires” →