Last time, we’ve looked over FET basics, details, nuances and caveats. Basics aren’t all there is to FETs, however – let’s go through real-world uses, in all their wonderful variety! I want to show you a bunch of cool circuits where a friendly FET, specifically a MOSFET, can help you – and, along the way, I’d also like to introduce you to a few FETs that I feel like you all could have a good long-term friendship with. If you don’t already know them, that is!
Perhaps, that’s the single most popular use for an NPN transistor – driving coils, like relays or solenoids. We are quite used to driving relays with BJTs, typically an NPN – but it doesn’t have to be a BJT, FETs often will do the job just as fine! Here’s an N-FET, used in the exact same configuration as a typical BJT is, except instead of a base current limiting resistor, we have a gate-source resistor – you can’t quite solder the BJT out and solder the FET in after you have designed the board, but it’s a pretty seamless replacement otherwise. The freewheel (back EMF protection) diode is still needed for when you switch the relay and the coil produces wacky voltages in protest, but hey, can’t have every single aspect be superior.
The reason you can drive it the same way is quite simple: in the usual NPN circuit, the relay is driven by a 3.3 V or a 5 V logic level GPIO, and for small signal FETs, that is well within Vgs. However, if your MCU has 1.8 V GPIOs and your FET’s Vgs doesn’t quite cut it, an NPN transistor is a more advantageous solution, since that one will work as long as you can source the whatever little current and the measly 0.7 V needed.
Continue reading “FET: Fun Endeavors Together”
[Nick Poole] over at SparkFun was playing with some force resistive strips. He wanted to use them as a keyboard input. It occurred to him that the office laminator could feasibly laminate a sheet of paper and the resistor into one sealed piece.
He put the assembly inside the pouch, ran it through the laminator, and it worked! After this success he built on it to make a full resistive keyboard. Then it occurred to him to ask, as it would to any good hacker with access to expendable company property “what else can I laminate”? Basically everything.
His next experiment was an LED throwie. No problem. Bolstered by the battery not exploding, he got more creative. The next victim was one of SparkFun’s Arduino-compatible boards and his business card. Success again.
Finally he went full out. Since the input rollers to the laminator are soft silicone it can apparently accommodate a fair amount of variance in height. He threw a full noise maker keyboard with resistive pads and a USB cable into the assembly. No issue.
It seems like a pretty good technique for making keyboards, weather proof circuits, and more.
Arduino fanatics rejoice: Autodesk and Circuits.io have jointly released a new electronics design tool with some unique features: 123D Circuits. Anyone familiar with Autodesk knows they have a bit of a habit of taking over the world, but you can relax knowing this is a (pretty much) free product that’s filed under their Free 3D tools—though we’re not quite sure what is “3D” about a circuits layout program.
123D is web-based software, and using it requires account creation on the circuits.io website. Anything you design sits on the cloud: you can collaborate with others and even embed your circuit (with functioning simulation) straight into a webpage. Unfortunately, your work is public and therefore accessible by anyone unless you fork over $12 or $25 monthly: the former only gives you 5 private circuits. Dollar signs pop up again when you hit “finish circuit;” they offer to sell you PCBs in multiples of three.
Some features of the free account, however, may tempt the Arduino veteran away from a go-to program like Fritzing. Plopping in a virtual Arduino lets you edit its code on the fly in another window, which you can then simulate. If you’re new to circuit design or want some guidance for using 123D Circuits, they have provided an extensive list of applicable Instructables. Check out their promotional video below.
Continue reading “123D Circuits: Autodesk’s Free Design Tool”
We missed 60% of it already, but luckily you can easily watch the back catalog of [Alan Yates’] 2011 Advent Calendar of Circuits. As with traditional Advent Calendars he’s got a treat for every day in December leading up to Christmas. Instead of chocolate, the treat is a video about a different electronic circuit.
We didn’t find a playlist link, but you can just head over to his YouTube channel as each day is clearly labelled in the video titles. He starts off with a current limiting voltage regulator. A couple of days later he busts out a metal detector that will be fun to play with. Day 7 brings an AM transmitter/receiver pair, and Day 12 illustrates a burnt-out Christmas light detecting tool which we’ve embedded after the break.
The sheer volume of projects he’s putting out every day is remarkable and delightful. He doesn’t even limit himself to one video a day, but has posted several ‘extra’ editions with quick, circuit demos. Continue reading “Advent Calendar Of Circuits”
If you’ve never heard of “Manhattan Style” circuit construction, you’re not alone. Popular in ham radio circles, the process looks nicer than straight dead bug style circuit building, but not as involved as etching your own PCB – consider it a nice middle of the road solution.
This type of construction is often used to build circuits inside enclosures that are made of copper clad, which is a somewhat common practice among ham radio operators. Manhattan Style circuits are built using glued-on metal pads to which components are mounted. One might think that the large pads you see in the image above would limit you to through-hole components, but that’s definitely not the case. A wide array of SMD pads are available in common pin configurations as well, allowing you to use pretty much any type of component you prefer.
While it might not be appropriate for every project you work on, Manhattan Style circuits and copper clad boxes definitely add a nice touch to certain items, like the Wheatstone Bridge Regenerative Receiver you see above.
Why spend time etching circuit boards and applying solder masks when all you really need is a rollerball pen and some paper? That’s what University of Illinois professors [Jennifer Lewis and Jennifer Bernhard] were asking when they set off to research the possibility of putting conductive ink into a standard rollerball pen.
The product of their research is a silver nanoparticle-based ink that remains liquid while inside a pen, but dries on contact once it is applied to a porous surface such as paper. Once dry, the ink can be used to conduct electricity just like a copper trace on a circuit board, making on the fly circuit building a breeze.
Previous ink-based circuit construction was typically done using inkjet printers or airbrushing, so removing the extra hardware from the process is a huge step forward. The team even has some news for those people that think the writable ink won’t hold up in the long run. The ink is surprisingly quite resilient to physical manipulation, and they found that it took folding the paper substrate several thousand times before their ink pathways started to fail.
While we know this is no substitute for a nicely etched board, it would be pretty cool to prototype a simple circuit just by drawing out the connections on a piece of paper – we can’t wait to see this come to market.
A large part of science is making mistakes and learning from them in order to make each subsequent design that much better. When your experimentation involves hacking cakes, each failure is an exercise in deliciousness.
[Craig] and his group of research partners often bake electronics-related cakes whenever part of the team departs in search of other opportunities. Over the years, farewell parties have seen renditions of anything from multimeters to quantum computers. This time around, he wanted to make something that contained actual electronics parts, while still remaining edible.
He settled on making an LED matrix inside of a cake, using silver foil wrapped licorice for wires. In the end however, he found the silver foil to be incredibly difficult to work with, and the matrix ended up being little more than a few randomly blinking LEDs.
Even though things didn’t work out quite how he planned, he is not discouraged. The cake was still quite tasty, and through this process he has discovered edible silver paint, which will undoubtedly make it into the next farewell cake.