Thursday, November 25, 2010

Electric Pea : How to connect vibration motor to arduino

I wanted to make an "electric pea" to my artwork : The Real Princess ( based on H.C.Anderssens fairytale the Princess and the Pea).  The idea was that when a person lays down to the bed, he/she would feel some odd vibration in his/her back. He or she could then imagine actually feeling the pea that was put under 20 mattresses.


The idea was to implement this by sewing a textile switch on to the  upper side of a thin matress (about 3 mm thick) and the vibration motor to the backside of the mattress. The weight of the person would trigger the textile switch and start the motor.

 I though that this task would be quite easy to manage.  I already had bought a pressure sensitive textile switch made by PlugandWear


I just needed a small vibration motor. They are easily available from any electric shop that sell Sparkfun products (product code ROB-08449).


The basic consept was that when someone was laying above the pressure sensitive switch, Arduino receives a signal to one of its input ports. Arduino would then steer the motor to vibrate until the pressure sensitive switch was again open (no pressure detected).

However I didn't want to use Arduino as a power source for the vibration motor for safety reasons. (Arduino is pushing 3,7 V - 4.9 v through the pins, and the vibration motor is operating at 2,5 - 3,8 V range.) Thus I needed external power source for the motor, a transistor to control the motor, and couple of resistors.

I was even able to draw the circuit diagram by myself:


Then troubles began.

I made an initial circuit to the protoboard.I downloaded the datasheet for transistor (BC639) from the web in order to figure out the correct pin order. I was sure that I had not made any mistakes - but the vibration motor was not running!!! I debugged sw and calculated the correct resistor values - nothing helped.

Luckily my husband still remembered how transistors can be used as diodes by short circutting the base and the collector of a transistor and using its two terminals as two terminals of PN junction diode. By measuring all the pins this way, he figured out the the datasheet that I had downloaded was not valid to my transistor (even the name of the transistor was the same !!) After figuring out the correct pin order of the transistor - everything worked fine.

The next problem was related to the pressure sensitive textile switch. The wires in the switch are very weak and almost as thin as human hair. They broke easily and are very difficult to connect to any "normal size" wires. The manufacturer instructs to use small uninsulated boothlace ferrules. I did have those, but still the connection was very sensitive to any movement of the wire. Finally I got the pressure sensitive switch working on top of my table (hard material below the thin matress), but the switch was not working properly on top of a soft matress I intented to use in my princess bed. :-(

I also noticed the the vibration of the motor was not strong enough to be noticed if there was any soft material below the motor.  :-(

And I also heard that the museum where the work was exhibited had to forbid people to climb to the bed. The bed is 280 cm high and does not have any safety railings. Still the parents were allowing very small kids to climb into it. Seems that parents do not have any common sense any more. :-(

Even though the project did not progess how I wanted, I learned many good lessons about transistors and textile switches. I am still planning to make a pressure sensitive switch totally by myself someday in the future.

Monday, November 1, 2010

Robots don't cry?

My art piece: ROBOTS DO NOT CRY? is currently presented at juryed exhibition ARTISTS 2010 by Finnish Artist association. Exhibition has 93 artworks that were selected from 1841 proposed ones.



The exhibition is at Tampere, Finland. My work is at Galleria Nottbeck. The exhibition is open during 30.10.-5.12.
The artwork consist of three robot balls that are covered by woolknit. These robotballs present crying songs (laments) that describes different feelings from joy, frustration, and sorrow. The crying songs have been traditionally presented at funerals, weddings, and other social situations. While presenting the songs, they also move slowly.

More information about this work can be found from my web pages.

Robot platform for lamenting robot balls

Here is the first prototype of my three-wheel robot.  At downstairs, there are Arduino Duemilanoa + Adafruits motorshield and all batteries. Upper part accommodates Arduino Mega+Xbee + MP3 trigger + speakers. This beauty is going inside a textile covered ball. After that he is ready to perfom to the audience.



Instruction how I made this robot and also the framework of the arduino software is published in my homepages.

Arduino + Xbee shield

If you have Arduino Xbee shield with XBEE Series 2, you should know that actually the module is now called XBee Znet 2.5.




Luckily I found these instructions from the web: http://blog.didierstevens.com/2009/06/15/quickpost-arduino-xbee-shield-series-2-configuration/ and I was able to continue in my project.

I also  run into mysterious "Arduino booting when Xbee was connected" problem. By browsing Arduino Forum I finally found the reason http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1217201592/0or http://rubenlaguna.com/wp/2009/03/05/setting-xbee-to-sleep-causes-arduino-reset/.

However I have not found any good solutions how this problem can be solved. I myself modified my software so that the "coordinator" of the xbee network sends some "Do-Not-Fall-In-Sleep" signals from time to time to other xbee modules in the network.

Playing music with Arduino + VMUSIC2

23.5.2009 I got first sound out of Mp3 player that was controlled by arduino. I used VMUSIC2 module, which can play mp3 files from USB memory stick.


I needed to update the firmware in order to make it working with all available commands (for example volume control).

VMUSIC2 module is not very well documentes so big thanks goes to Arduino forum for good hints (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1187669098) and http://www.instructables.com/id/Getting-started-with-VMUSIC2

After updating the firmware, the VMUSIC2 started behaving like the manual described.

After reading the manual more carefully, I noticed that the MPEG3 chip was actually a product of VLSI solutions - A Finnish company located about 300 meters from my working place at the same campus.

Well now I certainly know where I will call if I am having problems with VMUSIC2 mp3 decoding :-)
See also following links for useful information: http://byungjun.pe.kr/xe/?document_srl=20431 and Vmusic-tips-and trics

Eventually, I did not use VMUSIC2 because all USB sticks I found were too big to fit properly to the robot chassis I was building. Instead I used MP3 Trigger with microSD card. 

Welcome to my new blog

First posts in this blog are collected from my homepage http://www.outiaho.fi/.

I started to publish  some of my findings about electrical components that I was using in my lamenting robots. I originally made these robots for my final work to University of the Art and Design Helsinki. My Master of Arts thesis discussed about emotional machines and their role in the future society.