[Johannes] just sent us a tip about his small plotter that plots out the current time.
[Johannes] small clock plotter uses a dry wipe pen to write out the time on a small piece of dry erase board. The design is Made of three small 9g servos, with one to lift the pen off the writing surface and the other two to control a pair of connected jointed arms for the x and y-axis.
The little robot painstakingly wipes away the previous time before scrawling the current time in its place (with minute accuracy).
[Johannes] had hackability in mind when creating this project, making sure to keep to standard parts and making the code and design files available. The hardware for the build can be laser cut or 3D printed. The Arduino sketch can be found on GitHub and the design files can be found on Thingiverse. There are more detailed build instructions on Nuremberg’s FabLab page (translated). Continue reading “A Clock That Plots Time” →
Just when you thought you’d seen an Arduino do everything, [birdyberth] built an Arduino powered Electrocardiogram (ECG or EKG). Electrocardiography is a non invasive method of studying the heart. For many of us that means a 10 minute test during our yearly physical exam. Medical grade ECGs can use up to 10 electrodes. To keep things simple [birdyberth] went the route of a few circuits we’ve seen before, and reduced it to two electrodes and a ground reference. [birdyberth] makes note that the circuit is only safe if battery power is used.
The “heart” of any ECG is an instrumentation amplifier. Instrumentation amplifiers can be thought of as super differential amplifiers. They have buffered inputs, low DC offset, low drift, low noise, high open loop gain, and high impedance among other favorable characteristics. The downside is cost. A typical op amp might cost 0.50 USD in single piece quantities. Instrumentation amplifiers, like [birdyberth’s] INA128 can cost $8.30 or (much) more each. The extra cost is understandable when one thinks about the signals being measured. The ECG is “picking up” the heart’s electrical signals from the outside on skin. On commonly used ECG graph paper, a 1mm square translates to about .1 mV. High gain and clean signals are really needed to get any meaningful data here.
Electrodes are another important part of an ECG. Medical grade ECG units typically use disposable adhesive electrodes that make a strong electrical connection to the skin, and hurt like heck when they’re ripped off by the nurse. [birdyberth] was able to make electrodes using nothing more than tin foil and paper clips. We think the real trick is in the shower gel he used to make an electrical connection to his skin. While messy, the gel provides a low resistance path for the tiny currents to flow.
The actual processing in [birdyberth’s] circuit is easy to follow. The signal from the instrumentation amplifier is sent through a low pass filter, through a 741 op amp, and then on to the Arduino. The Arduino uses a 16×2 LCD to display heart rate in beats per minute, along with a friendly message informing you if you are alive or dead. The circuit even provides audible feedback for heart beats, and the classic “flatline tone” when the users either disconnects the electrodes or expires. [birdyberth] has also plugged in his pocket oscilloscope just after the low pass filter. As his video shows, the familiar ECG waveform is clearly visible. We’d love to see a more complex version of this hack combined with [Addie’s] heart simulator, so we could know exactly which heart malady is killing us in real time!
Continue reading “Arduino Powered ECG Informs Users Of Their Death” →
Feeling a little black-smithy? Ever wanted to hammer some red-hot steel into a new shape? Turns out, it’s well within your reach!
We’ve seen soup can forges, paint can forges, and even full blown coal fired forges — but none quite as simple as this. All you need is a fire brick — and some tools.
The problem is, fire bricks are kind of fragile. In order to drill into it without cracking the brick [Mike] advises us to clamp it in a wooden jig to help support it. Slowly drill a long hole lengthwise in it, slightly oblong to allow for your work piece to go inside. Flip the brick sideways, and add a second perpendicular hole in order to insert your gas torch of choice.
Now before you go heating it up, it is wise to reinforce the brick by wrapping some wire around it to prevent it from falling apart when it inevitably cracks due to temperature changes. A more permanent solution is to encase the entire brick in concrete to make it more durable, which [Mike] plans on doing next time. Continue reading “Mini-Forge On A Budget” →
Have you ever wanted to build a high quality audio crossover and amplifier? [Rouslan] has put a lot of thought into making his dual amplifier studio monitor both high quality and simple to build.
With a concise schematic, a meaningful block diagram, and simulation results to boot, his well-written post has everything you need to build self-powered bi-amped speakers based on the LM4766 from Texas Instruments. It is great to see simulations which verify the functionality of the circuit, this can go a long way when working with complicated analog filters and audio circuitry. For those of you who do not have access to PSPICE (an expensive professional simulation tool), [Rouslan] uses LTspice from Linear Technology. TINA-TI from Texas Instruments is another great free alternative.
Additionally, [Rouslan] goes over the typical issues one has with a bi-amplifier studio monitor, such as phase misalignment and turn-on pop, and then provides a solution. Note that his project is powered by 20VAC, which requires an external transformer to convert the 120VAC in the wall to 20VAC. Be careful with high voltages! In the future, adding a high quality voltage regulator will most likely increase the performance.
His post finishes up with a very clean circuit board, which he ordered from OSH Park. With such a complete design, there is nothing keeping you from building your own. Go out and put that old speaker sitting in your basement to good use!
If you don’t have an old speaker sitting around, check out these very cool DIY speakers.
Mold making is a hacking skill we see pop up around here from time to time. But rarely do we hear about problems in the process, and they must happen. Here’s proof. This Fail of the Week focuses on [Michael’s] unfortunate experience with failed mold making due to uncured silicone around the master mold. It’s worse than it may sound, since he lost about a pound of silicone to the fail, and we’re unsure of whether he can even use the master again (how do you clean uncured silicone off of something?). Not to mention the time lost from setting up the pour and waiting 20 hours for it to cure.
Soon after the issue presented itself [Michael] started researching to see what had gone awry and noticed that the master should have been sealed with acrylic lacquer. This gave him the opportunity to test several different finishes before making a run at the full mold once again. He picked up a variety of the paint products he could find locally, used them to coat some scraps, and globbed on some silicone to see which worked the best. He found a couple of different primers worked well, as did both glossy and matte acrylic coatings.
If you’ve never had a reason for mold making before, keep it in mind. You’d be surprised what kind of factory-production-type things can be pulled off by 3D printing a master, and casting a silicone mold of it.
Fail of the Week is a Hackaday column which runs every Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.
Last super bowl Sunday, instead of checking the game, [Mattw] decided to extend a design and make a PCB of a trinket clone. [Mattw] altered a trinket clone design by [Morgan
Penfield Redfield] to shrink it down, perforated the USB connector to allow for easy removal and put most of the parts on a single layer.
After finalizing the design, [Mattw] put it into the LPKF Protolaser S that Seattle’s Metrix Create Space has. For those of you who don’t know, the LPKF protolaser uses a laser to directly ablate off the copper from the boards. This makes prototyping much faster without the need for a lot of nasty chemicals.
About six minutes in the Protolaser, some component placement by hand followed by a run through their reflow oven and [Mattw] had three boards ready to be tested. All told, about 4 hours from start to finish.
The end circuit looks great and the LPKF protolaser gives us a case of serious tool envy. If you’re like us and don’t have access to the fancy laser you might try our hand at this high-resolutino photo-etch process.
Ever need a cheap motion tracker for very basic object following? Did you know you can throw one together with a few IR distance sensors and a PIC?
The setup is fairly simple. [Aron Horan] is using a dsPIC30F4011 PIC, a SHARP infrared distance sensor, an RC servo, and a PICkit2 for testing. It works by scanning left and right using the servo motor. When the edge of an object is detected, it will turn away from the object until it can no longer detect the edge — then it turns back. Unfortunately this does mean it will always be twitching, even when it’s tracking an object.
Like many of the other projects [Aron] has documented, he’s included everything you need to know to be able to recreate the project yourself. Flowcharts, wiring diagrams, and the code — written in C of course! The following video includes an excellent demonstration, but if you want to skip straight to the action, you can see it start tracking a multimeter at about 0:39 in.
Continue reading “Motion Tracking On The Cheap With A PIC” →