[Eric] needed a project for his digital logic design class, and decided on a lock that open in response to a specific pattern of knocks. This is a fairly common project that we’ve seen a few builds with ‘knock locks,’ but this one doesn’t use a microcontroller. Instead, it uses individual logic chips.
The lock senses the knocks with a piezo, just like every other build we’ve seen. Unlike the other builds, the knock pattern is then digitized and stored in an EEPROM. [Eric] only used 12 chip for this build, a feat he could accomplish with a few digital tricks, like making an inverter by tying one XOR input high.
We’ve seen a 555-based knock lock before, but getting the timing right with that seems a little maddening. [Eric]’s build seems much more user-friendly, and has the added bonus of being programmed by knocking instead of turning potentiometers. Check out [Eric]’s knock lock after the break.
Continue reading “Knock lock with logic chips”
[Snypercat] makes no bones about the fact that she despises rats, and does everything in her power to keep them off her farm. We can’t blame her though – they spread disease, eat other animals’ food, and can get your farm shut down if there are too many running about. While most of us might hire an exterminator or set out a ton of traps, she chooses to take a far more hands-on approach, hunting down each and every one of those little buggers with an air rifle.
If you’ve ever gone rat hunting in the dark (and who hasn’t?), you know that it can be difficult to aim in the dead of night. Night vision scopes can be expensive, but [Snypercat] shows how you can make your own scope that gives you the added benefit of recording your kills along the way. She happened to have a Sony camcorder with built-in night vision capabilities, and with a bit of tweaking she was able to mount it on her rifle’s scope. An IR flashlight was mounted on the rifle as well, giving her enhanced visibility without spooking her prey.
Be sure to check out the pair of videos below to see how [Snypercat] attached the camcorder to the scope, along with how well it works in the field.
Continue reading “Hunting down farmyard pests with technology”
Reader [Xellers] sent in his newest instructable: DIY Electron Accelerator: A Cathode Ray Tube in a Wine Bottle. While not exactly what you might think of a cathode ray tube, the basics are in place. A wine bottle is used as a vacuum chamber and a 9kv neon transformer is attached to a stopped in the top. A cathode is placed mid way, the air is sucked out with a pump, and high voltage is applied.
Naturally as more air gets pumped out the electric arc intensifies into a pretty solid plasma filling the space between the two contacts. While mixing drilled glass with a vacuum and high voltage sounds like an awesome hospital story [Xellers] does cover some safety points including the possibility of this thing putting out some nasty waves.
One thing that is not mentioned (that I saw) is this is very similar to how florescent light tubes work and without florescent material lining the chamber it will spit out quite a bit of UV light (notice germicidal UV lights are clear). So you will want to watch your eyes!
Join us after the break for a quick video.
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We’re all familiar with IVRS systems that let you access information using a touch-tone telephone. [Achu Wilso] built his own version which uses a cellphone, microcontroller, and computer.
The cellphone is monitored by an LM324 op-amp with an attached 555 timer chip. When a call comes in the voltage on the headphone output goes high, activating the timer circuit. If it goes low and does not go high again for about 25 seconds the call will be ended. Each incoming touch tone acts as a keepalive for the circuit.
An MT8870 DTMF (touch tone) decoder chip monitors the user input. An ATmega8 microcontroller grabs the decoded touch tones from that chip, and pushes them to a PC via USB. The PC-side software is written in Python, using MySQL bindings to access database information. eSpeak, the open source speech synthesizer software is used to read menu and database information back to the caller.
Not a bad little system, we wish there was an audio clip so we could hear it in action.
[Evan Flint] and his wife use a lot of online recipes in the kitchen. Rather than printing them out, they bought an iPad as a cooking companion. But in their cramped kitchen he needed to find a place for the high-end hardware that is out-of-the-way yet accessible. Some head scratching and parts bin diving led to this under-cabinet iPod dock.
The dock itself is a cradle made out of sheet aluminum. After cutting to shape, [Evan] bent up the sides and bottom to center the iPad. Since this is not a permanent fixture he needed to make the cradle collapsible. He used a CAD program to design the base tray to let the cradle lay flat, while giving several options to the angle when it is in use. Once the cooking is done just fold it up and the drawer slides make for easy under-cabinet storage.
Because he doesn’t own the house he didn’t want to make permanent alterations to the cabinet. But he does lament the unfinished look of the drawer slides. We’d just grab some pre-finished oak crown molding from the home store and wrap the entire thing. The left-edge of molding could slide out with the cradle when in use.
[Ben Krasnow’s] water vortex machine has been an exhibit in the lobby of the San Jose City Hall for quite some time now. Unfortuantely he recently had to perform some repair work on it due to the parts inside the water chamber rusting.
This is the same water vortex that we saw about a year ago. It uses a power drill to drive an impeller at the bottom of a water column to produce the vortex. That impeller was made from painted steel and after being submerged for eight months it began rusting, which discolored the water. [Ben’s] repair process, which you can watch after the break, replaces the shaft and the impeller. He reused a plastic PC cooling fan as the new impeller. The replacement shaft is stainless steel, as is all of the mounting hardware that will be in contact with water. But for us, the most interesting part of the repair is his explanation of the shaft gasket and bearings. Two thrust bearings and two radial bearings ensure that the shaft cannot move axially, which would cause a problem with the gasket. He had intended to swap out the oil seal for an all Teflon seal but the machined acrylic wasn’t conducive to the part swap. Instead, he replaced it with the same type of gasket, but bolstered the new one with some silicone to stave off corrosion.
Continue reading “Water vortex exhibit repair gives a look at the bearing and gasket design”
After a bit of inspiration, [Pete] decided to build a solid body electric guitar for himself. Instead of assembling a conglomeration of off-the-shelf parts, he plans on building just about everything from scratch. This includes the guitar pickups, so he built himself a pickup winder that has measures RPM, ETA until done, and auto stop for when the pickup is complete.
Electric guitar pickups are simple devices – just a magnet for each string wrapped in thousands of turns of wire about as thin as a human hair. [Pete] began his build with a cheap sewing machine and added a tachometer and pickup mount. As an added bonus, [Pete] threw in an ohmmeter to measure the coil resistance and a Gauss meter to measure the magnetic flux and polarity of the pole pieces. It’s a very nice build that’s designed to be as functional as commercial pickup winders.
[Pete] was originally inspired to build a pickup winder by the Les Paul Google doodle, and he plans on continuing Les Paul’s tradition of guitar innovation by building his own solid body guitar. The wood has been cut already, and we can’t wait to see the final product.
Check out a video of [Pete]’s coil winder in action after the break.
Continue reading “Guitar pickup winding workstation”