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NVMe Boot Finally Comes To The Pi Compute Module 4

March 29, 2021 by 4 Comments

Since the introduction of the Raspberry Pi Compute Module 4, power users have wanted to use NVMe drives with the diminutive ARM board. While it was always possible to get one plugged in through an adapter on the IO Board, it was a bit too awkward for serious use. But as [Jeff Geerling] recently discussed on his blog, we’re not only starting to see CM4 carrier boards with full-size M.2 slots onboard, but the Raspberry Pi Foundation has unveiled beta support for booting from these speedy storage devices.

The MirkoPC board that [Jeff] looks at is certainly impressive on its own. Even if you don’t feel like jumping through the hoops necessary to actually boot to NVMe, the fact that you can simply plug in a standard drive and use it for mass storage is a big advantage. But the board also breaks out pretty much any I/O you could possibly want from the CM4, and even includes some of its own niceties like an RTC module and I2S DAC with a high-quality headphone amplifier.

Once the NVMe drive is safely nestled into position and you’ve updated to the beta bootloader, you can say goodbye to SD cards. But don’t get too excited just yet. Somewhat surprisingly, [Jeff] finds that booting from the NVMe drive is no faster than the SD card. That said, actually loading programs and other day-to-day tasks are far snappier once the system gets up and running. Perhaps the boot time can be improved with future tweaks, but honestly, the ~7 seconds it currently takes to start up the CM4 hardly seems excessive.

NVMe drives are exciting pieces of tech, and it’s good to see more single-board computers support it. While it might not help your CM4 boot any faster, it definitely offers a nice kick in performance across the board and expands what the system is capable of. Continue reading “NVMe Boot Finally Comes To The Pi Compute Module 4” →

A Tiny Tube Amp For Not A Lot

March 7, 2021 by 49 Comments

At the extreme budget end of tube audio lie single-tube amplifiers usually using very cheap small-signal pentodes. They’ve appeared here before in various guises, and a fitting addition to those previous projects comes from [Kris Slyka]. It’s a classic circuit with a transformer output, and it provides enough amplification to drive a pair of headphones or even a speaker at low levels.

The fairly conventional circuit of the tube amplifier.

Most tube enthusiasts will instantly recognize the anode follower circuit with a transformer in the anode feed through which the output is taken. The tube works in Class A, which means that it’s in its least efficient mode but the one with the least distortion. The transformer itself isn’t an audio part, but a small mains transformer taken from a scrap wall wart. It serves not only for isolation, but also to transform the high impedance output from the tube into a low impedance suitable for driving a headphone or speaker.

The HT voltage is a relatively low 24 V, but it still manages to drive headphones acceptably. Speaker levels require a pre-amp, but even then it’s likely that this circuit is pushing the tube beyond what it’s capable of with a speaker. The more it operates towards the edge of its performance envelope the more distortion it will generate and the worse a sound it will produce. This isn’t such a problem in a guitar application as here, but hi-fi enthusiasts may find it to be too much. It would be interesting to subject it as a headphone amplifier to a series of audio tests to evaluate the effect of a mains transformer over a dedicated audio one.

Last year we took a very in-depth look at the commonly-available Chinese kit pre-amps that use a similar anode-follower circuit but without the transformer. We’ve also seen a similar amp that uses an op-amp as an impedance converter, as well as a novel take on the idea whose unusual biasing allows it to run from only 3.3 volts. These circuits can be so cheap to get started with that we’d suggest anyone give them a try.

A PCB For A Quarter?

February 27, 2021 by 19 Comments

As time has gone by and PCB assembly companies have reached further into the space of affordability for our community, the available types of board have multiplied. No longer are we limited to FR4 with a green solder mask, we can have all colours of the rainbow and a variety of substrates. The folks at BotFactory have taken things a step further with their PCB printer though, by printing a fully-functional PCB on a quarter.

As a base layer the printed five passes of insulation on the coin, before printing the traces. Holes are left in the insulation to create a form of via that connects to the coin. On the board is an ATtiny2313 microcontroller that flashes an LED, and on the reverse side of the coin is a CR2032 cell that’s secured with a set of bolts and washers. You can see it taking shape in the video below the break.

It’s true that an LED flasher isn’t exciting, and that this is a marketing stunt for BotFactory’s printer. But it’s an inventive one, and reminds us that with a bit of ingenuity anything can become a board. We’ve had our share over the years, and instantly springing to mind is this stretchable PCB.

Continue reading “A PCB For A Quarter?” →

Exploring The Open Source That Really Goes Into A RISC-V Chip

February 27, 2021 by 19 Comments

It’s an exciting time in the world of microprocessors, as the long-held promise of devices with open-source RISC-V cores is coming to fruition. Finally we might be about to see open-source from the silicon to the user interface, or so  goes the optimistic promise. In fact the real story is considerably more complex than that, and it’s a topic [Andreas Speiss] explores in a video that looks at the issue with a wide lens.

He starts with the basics, looking at the various layers of a computer from the user level down to the instruction set architecture. It’s a watchable primer even for those familiar with the topic, and gives a full background to the emergence of RISC-V. He then takes Espressif’s ESP32-C3 as an example, and breaks down its open-source credentials. The ISA of the processor core is RISC-V with some extensions, but he makes the point that the core hardware itself can still be closed source even though it implements an open-source instruction set. His conclusion is that while a truly open-source RISC-V chip is entirely possible (as demonstrated with a cameo Superconference badge appearance), the importance of the RISC-V ISA is in its likely emergence as a heavyweight counterbalance to ARM’s dominance in the sector. Whether or not he is right can only be proved by time, but we can’t disagree that some competition is healthy.

Take a closer look at the ESP32-C3, with our hands-on review.

Continue reading “Exploring The Open Source That Really Goes Into A RISC-V Chip” →

Taking A Capacitor Microphone To The Next Level

February 24, 2021 by 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 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 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” →