9:00: We are finally getting started! Everyone is busily gathering boards, resistors, capacitors and cables, unpacking newly arrived components or hurries away to buy those parts that are still missing. Some groups even seem to plan to integrate unusual components such as umbrellas, inflatable mattresses or small plastic bubbles into their prototypes.

13:00: How to solve  problems, you did not know existed? The more our concepts are progressing, the more challenges have to be faced. Some basic solutions for often occuring problems:

How to connect RGB LED strips?

1. Connect the strip.  You find four wires attached to the copper tabs. In our example (left picture below) we have from left to right:

  • white coating: green LED color
  • yellow coating: red LED color
  • black coating: red LED color
  • red:  +12V

Some ready-bought LED-strips already use color coding for the wires: white for the power supply and then red, green and blue wires for the corresponding LED colors.

rgb stripe 2     rgb stripe 1

2. Set up the circuit. As our LEDs require more power than the arduino’s build-in power supply can provide, we have to connect an external power source and therefore need to add transistors to our circuit. In the setup used for the GLOW WORM LOVE project (right picture above), three N-channel MOSFETs for each single LED are used, which allows to actuate R, G, and B seperately.

circuit setup

[picture from: http://www.ladyada.net/products/rgbledstrip/ ]

3. Control your LEDs

In the Arduino sketch for every LED, the channels are defined:
void setup () {

pinMode(REDPIN, OUTPUT);
pinMode(GREENPIN, OUTPUT);
pinMode(BLUEPIN, OUTPUT);

}

and can now be assigned seperately to a specific value. For a nice purple we can use

analogWrite(REDPIN, 112);
analogWrite(GREENPIN, 0);
analogWrite(BLUEPIN, 112);

How to convert the sensor output of a LilyPad Temperature Sensor to  °C?

Usually it is sufficient to retrieve the raw values from the LilyPad Temperature Sensor, but sometimes, for example when you are designing user interactions, you would like to know the exact value in degree Celsius. So this is how you do it in your android-sketch:

1. Read the sensor output.
temperature= analogRead(yourInputPin);

2. Convert the achieved value to volt
voltIN = 3300;  //if you connected to 3.3V
voltIN = 5500; //if you connected to 5.5V
float voltOUT = temperature * (3300/1024);

3. Calculate the
factor =  19,8;  //19,8 mV per degree, if you are using a  MCP9701A
factor = 10,0; // 10 mV per degree, if you are using a MCP9700A
float tempC = voltOUT/faktor;


How to switch the direction of a DC motor?

For the blowfish group it is important to have a DC motor capable of switching its running direction. Therefore a circuit with relays is necessary. In fact, two relays are used. One to stop the motor and one to switch the current flow. The basic idea is to use a DPDT (double pole double throw) relay which separates two differently polarized circuits. Without activating the relay, the motor is +/- connected. When voltage is applied to the relay (the switch inside changes its position) the motor gets -/+ connected and runs in the opposite direction.

relay circuit

And some further creative workarounds for so far unknown challenges had to be found.

     

19:00: Time to go home. All five teams have already made substantial progress and the first premature prototypes are moving, blinking andmaking all kinds of nice sounds and less nice noises.

Some impressions:

led ball  team_work  umbrella1  umbrella 2

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