[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.
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.
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.
[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
[eclipsed78], built an automatic toroid winder. The drum splits in order to load the toroid. Then wire is wound on the drum, much like any other coil would be wound. The drum rotates as a slider pulls the wire off the drum, while revolving in and out of the toroid. A side tension keeps the slack out of the wire during operation. The winding coil is stepped as the drum rotates, in order to control the turns ratio. [eclipsed78] created a stepper driver from a schematic, so he could drive the motors. You can watch the winder in operation as a series of videos. The first of which is embedded below. If you have ever needed to wind a massive toroidal transformer, this is the project for you. Continue reading “Homemade toroid winder”