Generating high frequencies with AVR ATMEGA (Arduino)

While playing with the touch interface i generated high frequencies with the Arduino. I think this could be useful for other applications so here is the Arduino code for generating high frequencies. Here is a list of possible frequencies.

Bear in mind that the frequency resolution is very low at high frequencies and the duty cycle is not allays 50 %.

Arduino do the Touché dance

The Touché hardware uses a really fancy Direct Digital Synthesizer IC from Analog Devices. It generates a really pure sine wave signal with frequencies between 1kHz and 3.5MHz with crazy high resolution.

While the Arduino is capable of generating frequencies in this range the signal is a square wave with lots of harmonic frequency components and really low frequency resolution.

Simply using this signal with the circuit described in the Touché paper result in a really messy frequency graph due to the harmonics from the square wave.

The solution is to use the filtering properties of the LC circuit to our advantage. By measuring the signal after the inductor (coil) rather than before we only see a nice sine wave shaped signal free of all the unwanted frequency components.

As a result we now see a peak in signal at resonance rather than a notch but the signal contains the same information.

The Arduino is only able to generate about 200 frequencies within the usable frequency range but the signal measured at these frequencies is very clean and stable allowing for interpolation to get better resolution.

We are currently working on algorithms to determine touch gestures from this signal.

Here are some external links about the touch interface:

Original DisneyResearch paper

Instructable by Mads Høbye about how to make it

Online article (w. video) at MEDEA Malmö University

 More may be added.

Replicating Disney research Touché sensing method

A little while ago The people at Disney research released a video showing a new capacitive sensing techneque. We were all amazed over the result and expected some real electronic wizardry to be behind. After reading their paper about the subject it turned out that they used an effect we Tesla coilers often experience.
A tesla coil secondary is a big coil of wire with a doughnut shaped electrode connected to one and the ground to the other. This form what is called a LC resonator. The inductance of the wirer and the capacitance of the doughnut interact to give the whole assembly a specific resonance frequency. Changing either the capacitance or the inductance alters the frequency.
Another property of the assembly is that the ground wire seem to suck in signal at the resonance frequency. If the ground wirer is connected to the output of a signal generator it will draw current from the generator only at the resonance frequency.  Touching the top electrode or even approaching it alters the capacitance.
Assuming the inductance is constant the resonance frequency gives a measure for the capacitance in the system and thus the interaction.
Substituting the Tesla primary winding with a 10mH potted inductor and the top electrode with a roll of solder I replicated the sensing method used by Disney Recearch.

(Less crappy video)

Runner w. spool

Braider with spool-runners and spools

All the bits before attaching motor. 6 out of eventually 18 runners are tested.

Test video with motor

How the braider works

The braider uses 6 gears connected in a circle. Each gear drives a plate with 4 notches. The notches drives pegs mounted on spool runners (red and green dot). The runners are guided by a track following the movement of the grooves except where each of the gears meet. Here a switch track let the runners pass from one plate to another.

Maypole brading machine

While doing some 1910 era props i needed tubular braid around some wirers. I got interested in how these were made and thought I would to make a machine that does tubular braiding.

This is my first prototype:

The idea is that 18 spools are racing around each other in a Møbius knot like pattern. The result is the same as Maypole weaveing.
Here is a short video of the first results:

The method seems to work but I still need to design the actual spools and a sustem for advancing the finished braid.

Radiation detector

Had a bunch of empty coffie cans that i wanted to use for something. I found this article about using coffiee cans for ion chamber radiation detectors.
I did not have the parts they suggested so i used whateve i had:

The detector turned out to be extremely sensitive and should be able to pick up small changes in the background radiation. I plan to make a solar powered version that will sit in the window and keep a watch on things.

Say hello to my little (old) friend..

A couple of years ago I built this prototype power supply for a large CO2 laser. The interesting thing about it is that it completely microcontroller driven and uses a rare series resonant topology. It deliveres up to 30KV and an adjustable constant current of up to 25mA.
After considering it lost I was pleased to find it again.
I was able to get it running and decided to show some fruits who is the boss...

. 

As the picture from inside the power supply shows it is really simple consisting of only a few parts:

The power supply was originally inspired by this article

New enclosure for desktop CNC machine.

A couple of years ago I purchased a small CNC machine for PCB routing and drilling. I never really used it much then but recently I have started to as part of my quickly expanding prototyping lab.
After being annoyed by the noise and mess it makes in my office i decided to use it's bigger cousins to make an enclosure for it.

Students build rapid prototypes at Roskilde University

I was teaching a workshop on Rapid Prototyping for 2 weeks at Roskilde University.

Here 3 groups of students teamed up to build different parts of a tracked robot. One team built the driving base, one team the turret and one team a compressed air cannon that shoots ping-pong balls.
Overall a really fun project that resulted in a fully functional remote controlled vehicle.

Another group build this automated cake froster.

Quick test of new Solid State Tesla coil controller

Made a new micro controller based resonance controller for the exhibition Tesla coil. The design is very succesful and i'm really exited to try it on the actual Tesla coil secondary being build as I write. Until then the best I have is a roll of wire but as seen in the video a mere 37 volts on the driver circuit makes quite a remarkable spark. If left on for more than a few seconds the wire ends catch on fire :) (Murharhar!!)

240V detector

I needed a micro controller to detect if 240V mains was applied. This circuit works well.

Finished Tesla coil

Tesla coil ready for exhibition.

Short test video of the coil setting paper on fire.

Video from Tesla building

More Tesla build pictures

Tesla coil , a set on Flickr.

We had another night of Tesla coil building. This time all circuits were tested and power applied for the first time.

Laser cut Lego compatible gears

Yes I do occasionally make stuff out of Lego. At some point I got annoyed that i only had up to 64 teeth gears and decided that i could make my own.

 For some other project I bought the excellent Gear template generator from woodgears.ca
After a bit of experimenting i found the parameters for making Lego compatible gears:

Tooth spacing: 3mm
Addendum: 0.350

When machining gears to exactly the measurements produced by the program you get a remarkably good fit.

Tesla 2012

Tesla coil , a set on Flickr.

A while ago i was asked to make a Tesla Coil for an exhibition about Nikola Tesla. I have previously experimented with traditional Tesla coils (Archive). These were loud, dangerous and not really public friendly devices.

A new generation of electronically controlled solid state Tesla coils have been emerging over the last couple of years and we decided that one of these were better suited for public display.

A side effect of the electronic control is the ability to play music. I find this feature rather corny but it seems to be a real crowd pleaser.

Here are the result of the first build night with my long-time Tesla buddy Marc.

Hide And Seek

I have been asked to make a device that allow a space capsule to be found at sea after splashdown. The device should transmit it's GPS position via. VHF radio to a fleet of recovery vessels.
The device should allow regular people without special equipment or training to receive the GPS position.
It was suggested to use plain speech to transmit a WGS84 GPS message that is compatible with most navigation equipment.

This is my initial approach to solving this problem.
First the numbers 0 to 9 and the words "East", "West", "North" and "South" was recorded using a digital recording program (Audacity). The audio file was cleaned and compressed so that the words had an equal voloume and the length was fitted to exactly 32 kSamples. The audio file was then converted to 8bit mono@8kHz .raw format. The start sample and duration of each word was noted.
A special program was made that would transmit the .raw file over a serial port. A 24C256 IIC EEPROM was connected to an Arduino board and a firmware was made to receive the .raw file and flash it into the 24C256.
The EEPROM now contained spoken words that could make up the WGS84 message and a list of starting points and durations for each word.
The firmware in the Arduino board (later to be replaced with custom hardware) was changed to a firmware that received GPS data in the form of NMEA and read these out using the words from the EEPROM.
The micro controller on the Arduino board outputs the audio as PWM which is low pass filtered to make a analog line signal. This signal will later be fed to a custom VHF transmitter that will be integrated as part of the system.

This is a audio test of the system so far. The voice is synthesized but will be replaced by a sexy female voice.

The GPS and audio chip

Active control of payload direction

By changing the set-point of the payload stabilizer the direction of the payload can be actively controlled. This could be useful for panning on-board cameras etc.
In this experiment set point was commanded to sweep between +90 and - 90 degrees with the following profile:

Red=yaw(roll), green=command, 20mS/div.

In the video the payload section vibrates a bit. This is a result of the loop-filter not being properly re-tuned after the motor driver was changed.