# Circuit VR: Oscillating Bridges

Circuit VR is where we talk about a circuit and examine how it works in simulation with LT Spice. This time we are looking at a common low-frequency oscillator known as the Wien bridge oscillator.

What makes an oscillator oscillate? A circuit with amplification that gets the same amount of the output signal fed back into its input, in phase, will oscillate. This is the Barkhausen criterion. Here, we’re going to look into what makes an oscillator work in simulation, and gain some insight into what happens when there’s too much feedback and too little.

In particular, we’ll look at the Wien bridge oscillator, a very simple design that originated as a way to measure impedance back in 1891. Modern versions add some additional features, but let’s start with the most simple implementation and work our way up.

# Circuit VR: The Dickson Charge Pump

There was a time when taking a low DC voltage — say a single battery — and converting it to a higher voltage was painful. Now, however, cheap and easy-to-use DC to DC converters are readily available. For some small tasks, though, these can seem like overkill. For example, consider a case where you need to supply a higher voltage for a MOSFET gate that doesn’t draw much current. Perhaps you need that higher voltage to trigger a microcontroller’s programming mode and nothing else. The current draw is minimal, and a full-blown DC to DC converter is overkill. For cases like that, it is tempting to use some voltage multiplication scheme. There are many, but for this post, I’m going to take you inside a Dickson charge pump. This is Circuit VR because not only are we going to discuss the circuit, we’ll look at an LT Spice simulation you can try yourself.

The Dickson is interesting because it doesn’t require any AC conversion or transformers. Instead, it uses diodes or other switching elements to transfer charge between capacitors in stages. Each stage will effectively increase the voltage by the supply voltage — in theory. Reality isn’t so kind, though, as we’ll see.

# Friday Hack Chat: Simulating Analog

Simulation is a valuable tool for any hardware developer. Instead of building hardware for a long debugging session, you can emulate a microcontroller and blink your lights with some Javascript. Instead of working on a Bluetooth protocol for your fitness wearable, you can just whip up some Javascript and get it working that way. Once all your Javascript is in order, then you can finally move over to hardware. It saves development time, and it saves money.

But this is all digital. What do you do if you’re working on an analog system? Lucky for you, there’s a system built for analog and mixed-signal analysis, and it’s been around for decades. This week we’re talking all about PSpice, a simulator for analog analysis that will give you voltages and currents across every node in a schematic.

For this week’s Hack Chat, we’re going to be talking about PSpice with [Abha Jain] and [Alok Tripathi]. [Abha] has worked at Cadence for 19 years and has been part of the PSpice R&D team for the last decade. She’s an MTech in VLSI Design Tools and Technology and holds multiple EDA patents. [Alok] graduated in 1993 with a B. Tech in Electrical Engineering. He started working at the Department of Atomic Energy in 1993 as a power supply and control system designer for particle accelerators. Currently, he’s working with Cadence and is the Product Engineering Architect for PSpice and OrCAD.

For this Hack Chat, we’re going to be discussing the challenges of system-level simulation, improving reliability, yield, and productivity of circuit design, the issues of Spice simulation, and answer the question, ‘on an infinite grid of one Ohm resistors, what is the resistance between two nodes a knight’s move apart?’ You are, of course, encouraged to add your own questions to the Hack Chat. You can do that by leaving the questions as a comment on this Hack Chat’s event page.

Our Hack Chats are live community events on the Hackaday.io Hack Chat group messaging. This week it’s going down at an unusual time: 8 AM Pacific, Friday, March 30th  Want to know what time this is happening in your neck of the woods? Have a countdown timer!

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io.

You don’t have to wait until Friday; join whenever you want and you can see what the community is talking about.

# Minecraft And Forge: Try This Amazing Way To Visualize Logic

I’ve got virtual circuits on the mind lately. There are a myriad of tools out there that I could pick up to satisfy this compulsion. But the one I’m reaching for is Minecraft. I know what you’re thinking… a lot of people think Minecraft is getting long in the tooth. But chances are you never tried some of the really incredible things Minecraft can do when it comes to understanding logic structures. This goes way beyond simple circuits and easily hops back and forth over the divide between hardware logic and software logic.

# LTSpice For Radio Amateurs (and Others)

We don’t think [VK4FFAB] did himself a favor by calling his seven-part LTSpice tutorial LTSpice for Radio Amateurs. Sure, the posts do focus on radio frequency analysis, but these days lots of people are involved in radio work that aren’t necessarily hams.

Either way, if you are interested in simulating RF amplifiers and filters, you ought to check these posts out. Of course, the first few cover simple things like voltage dividers just to get your feet wet. The final part even covers a double-balanced mixer with some transformers, so there’s quite a range of material.

# Make Mulled Wine With A Processor Heatsink!

Now, over the holiday season there seems to be a predilection towards making merry and bright. As many an engineer and otherwise are sure to note, fine alcohols will facilitate this process. One such warm holiday beverage is mulled wine; there are many traditions on how to make it, but a singular approach to preparing the beverage would be to re-purpose an old PC and a CPU liquid cooling unit into a mulled wine heating station.

Four years ago, [Adam] found himself staring at a pile of mostly obsolete PCs in his IT office and pondering how they could be better used. He selected one that used a power-hungry Pentium 4 — for its high heat output — strapped a liquid cooling block to the CPU and pumped it full of the holiday drink. It takes a few hours to heat three liters of wine up to an ideal 60 Celsius, but that’s just in time for lunch! The Christmastime aroma wafting through the office is nice too.

# It’s Time To Finally Figure Out How To Use KiCAD

KiCAD has been making leaps and bounds recently, especially since CERN is using it almost exclusively. However, while many things are the same, just enough of them are different from our regular CAD packages that it’s hard to get started in the new suite.

[Chris Gammell] runs Contextual Electronics, an online apprenticeship program which goes from concept to assembled electronics covering everything in between. To take the course you pay a nominal fee, but [Chris] posted a very excellent ten-part video series made during the last run of classes which you can watch without charge. The videos go through the basics of KiCAD while hitting the major points to consider when designing and manufacturing your electronics.

The project [Chris] chose is a simple circuit that blinks an LED with a 555. The first videos cover navigating KiCAD’s component schematic editor and library system. Next comes creating circuit schematics and component footprint creation. [Chris] covers PCB layout, the generation of Gerber files, and finally ordering the design from OSH Park — the purveyors of purple boards we’ve come to know and love. The series finishes up with simulating the circuit in LTSpice, ordering the parts, and finally soldering and debugging of the board. If all goes correctly you should now have a single blinking LED.

If the bright summer sun is burning your delicate skin, and you’d rather be locked inside with solder fumes, add this to your watch list now!