Adjustable Tesla coil build

This coil has no trouble shooting sparks across four meters of empty air. [Finn Hammer] has been putting in some long hours on this labor of love, and we put in some time reading through his progress thread. He started down this path about a year ago and every step of the way he produces beautiful work. We enjoy seeing his prototyping techniques, moving from concept to hand drawing to CAD diagram before starting the physical build. Check out the demo video after the break and as you read through his thread look for the green arrows that lead to other videos and resources.

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Power drill solder spooler

[Scott] over at curiousinventor.com has posted an instructable detailing how to use an Arduino and a power drill to spool solder. The Arduino senses the speed that the drill is going via an opto interrupter and a laser and adjusts with a servo hooked to the trigger. While we don’t think many people will be dying to spool some solder, this system might be useful for all kinds of things, like winding yarn or making coils.

RF transmission in the 9 KHz band

[W1VLF] is on a quest to communicate over long distances with a 9 kilohertz transmitter. He built this giant coil with that in mind. A round concrete form was used as a base and wound with magnet wire by hand. We’d recommend building an automated winding device, but this method seems to have worked. Operating at 50 Watts on the air-core coil at 8.97 KHz he was able to pick up the signal at a distance of 5 kilometers. It’s not breaking any overall distance or portability records, but on a project like this the quest is where the fun is at.

[Thanks Drone]

Arduino RFID spoofer

An Arduino, a spent roll of toilet paper, magnet wire, and a few passive components are what’s needed to build this RFID spoofer. It’s quick, dirty, and best of all, simple. However, [SketchSk3tch’s] creation is not an RFID cloner. You must already know the hex code of the tag you want to spoof. That may or may not be as easy as using a separate tag reader.

We’ve seen some very simple RFID tag concepts. What we want is a DIY reader that is easy to build from cheap and readily available components. If you’ve got one, make with the details and tip us off about it.

AVR boost converter

avrboost

Over at SpriteMods, [sprite_tm] realized that a microcontroller could be used as a boost converter to power itself. A boost converter steps up voltage from a battery by switching the output of a coil. First, it is tied to ground so a magnetic field can build up in the coil. It is then released as a higher voltage than the input. Normally dedicated chips do this at an incredibly high frequency, but the PWM signal from an AVR works well enough. This can be used in low-power situations where space is an issue.

[via EMSL]

AVR RFID tag

[pc486] sent in his hack that uses an ATtiny85 to act like an EM4102, a chip used for RFID tags. Minimally, all that is needed is the AVR and a coil, but he recommends some filtering capacitors. Depending on the size of the coil, different frequencies and ranges can be achieved. This project actually includes several hacks, such as using the coil for not only power, but a clock signal. The coil is actually able to power the chip without being connected to the power pins due to clamping diodes on the connected pins. The firmware is short but available on subversion.

Related: Scratch-built RFID tags