In the first article about measurement systems we looked at sensors as a way to bring data into a measurement system. I explained that a sensor measures physical quantities which are turned into a voltage with a variable conversion element such as a resistor bridge. There will always be noise in any system, and an operational amplifier (op-amp) can be used to remove some of that noise. The example we considered used an op-amp in a differential configuration that removes any disturbance signal that is common to both inputs of the op-amp.
But that single application of an op-amp is just skimming the surface of the process of bringing a real-world measurement of a physical quantity into a digital system. Often, you’ll need to do more work on the signal before it’s ready for sampling with a digital-to-analog converter. Signal conditioning with amplifiers is a deep and rich topic, so let me make it clear that that this article will not cover every aspect of designing and implementing a measurement system. Instead, I’m aiming to get you started without getting too technical and math-y. Let’s just relax and ponder amplifiers without getting lost in detail. Doesn’t that sound nice?
The physical world is analog and if we want to interface with it using a digital device there are conversions that need to be made. To do this we use an Analog to Digital Converter (ADC) for translating real world analog quantities into digital values. But we can’t just dump any analog signal into the input of an ADC, we need this analog signal to be a measurable voltage that’s clean and conditioned. Meaning we’ve removed all the noise and converted the measured value into a usable voltage.
Things That Just Work.
This is not new information, least of all to Hackaday readers. The important bit is that we rely on these systems daily and they need to work as advertised. A simple example are the headlights in my car that I turned on the first night I got in it 5 years ago and haven’t turned off since. This is not a daytime running lights system, the controller turns the lights on when it’s dark and leaves them off during the day. This application falls into the category of things that go largely unnoticed because simply put: They. Work. Every. Time. It’s not a jaw dropping example but it’s a well implemented use of an analog to digital conversion that’s practical and reliable.
The RF signal transmitted from a modern key fob and received by the associated vehicle is only used once. If the vehicle sees the same code again it rejects the command, however there is a loophole in those carefully chosen words. The code must be received by the vehicle’s computer before it can be added to the list of spent codes. [AndrewMohawk] goes through the process of intercepting a code sent from a key fob transmitter and preventing the vehicle from receiving it in a thorough post to his blog. You can see this attack working in his studio quality reenactment video after the break.
[Andrew] uses the YARD Stick One (YS1) which is a sub-GHz wireless tool that is controlled from a computer. The YS1 uses RfCat firmware, which is an interactive python shell that acts as the controller for the wireless transceiver.
This system is not without its problems: different frequencies are often used for different commands, [Andrew]’s scripts are designed to work with On-Off keying (OOK) leaving it useless when attacking a system that uses Frequency-Shift Keying (FSK). There is also the issue of rendering a target key fob non-functional but you’ll have to pop over to [Andrew]’s blog to read more about that.
[Lou’s] friends all said that it would be impossible to build a unicycle that had offset pedals. Moving the pedals to the front of the unicycle would throw off the balance and prevent the user from being able to ride it. [Lou] proved them wrong using mostly components from a single donor bicycle.
The donor bike gets chopped up into a much smaller version of itself. The pedals stay attached in the original location and end up being out in front of the rider. The seat is moved backwards, which is the key to this build. Having the rider’s legs out in front requires that there be a counter balance in back. Moving the seat backwards gets the job done with relative ease.
To prevent the hub from free wheeling, [Lou] lashes the sprocket directly to the wheel spokes using some baling wire. He also had to remove the derailer and shorted the chain. All of this gives the pedals a direct connection to the wheel, allowing for more control. The video does a great job explaining the build quickly and efficiently. It makes it look easy enough for anyone to try. Of course, actually riding the unicycle is a different matter. Continue reading “Offset Unicycle Built Mostly from a Single Bicycle”→
One thing very common to all of us is our reliance on operating systems in our hobby life. If that OS is Windows then you could be in for quite a shakeup with Windows 8. Many readers are Linux or Apple users and couldn’t care less if Microsoft is releasing an entire paradigm shift in desktop navigation. However, you just might find yourself facing this new OS and you’ll look like you’re on training wheels if you don’t get acquainted now, and considering the number of computers being released with Windows 8 its inevitable that day will come soon.
So if you haven’t been behind the wheel of Windows 8 then checkout [Steve’s] Windows 8 Survival Guide from the Guru Brew Tech Show. This is an excellent overview of the new touch screen navigation methods you’ll find in the Windows 8 desktop including hotspots, charms and tiles to name just a few. You’ll also learn tips to get around with a mouse and keyboard. It’s not a complete tutorial on using Windows 8 but you’ll at least know how to navigate, search for apps, work with multiple apps and find tools like task manager, control panel, file explorer as well as your familiar desktop.
Follow the break to watch the short survival guide video.
The requirement list is heavily influenced by the requirements needed to earn a merit badge in the Boy and Girl scouts – first, do a little research and be able to describe the type of build we usually feature. Then, describe the project to your teacher and directly relate your project to other builds featured on Hackaday. Solid advice, we have to say.
There’s a few solid tips that really help us out; putting up a blog post for your project really helps us out, as does hosting your code on a Git. Videos are always good, and even though I’m partial to Vimeo (these videos just come out looking more professional for some reason), a lot of our commentors prefer YouTube.
About the commentors: the requirement sheet specifically mentions ignoring the flame bait comments, something we’d have to agree with. The comments have gotten better, but the best way for you (yes, all of you) to help is just hit the report button and don’t feed the trolls.
If your post doesn’t make Hackaday, don’t feel bad. Before I started working here, I built a Mellotron and submitted it to the tip line. It didn’t get featured, but I just rolled with the punches. Now I’m waiting for a Raspberry Pi to come in so I can update that build and give it the rollout it deserves. If your build gets skipped, just re-submit a week or so later. We’re a fickle bunch and sometimes projects waste away in the tip line, especially if it’s similar to a recently posted build.
Every once in a while, the Hack a Day tip line gets a submission that is cool, but screams to be built in a few hours, possibly while consuming adult beverages. When [Shay] and [Ben] sent in their Manifold Clock Kickstarter, I knew what I had to do. To make a long story short, there’s a manifold clock hanging on my wall right now. Check out my manifold clock how-to guide after the break.