Sunday, December 13, 2015

PROJECT: Solar House

This year my partner and I managed to score some cheap solar powered lanterns along with some flickering LED candles at a garage sale, and with New Years being just around the corner I decided to convert them into a solar powered house with a nifty fireplace.

3D Models can be obtained from here, and build instructions can be found here.

Before I get into the nitty-gritty of things, below is the schematic for this project.


Solar Cells

Prior to actually using any solar cells it always a good idea to characterise them to see how well they perform. To do this I used your typical rheostat to place a variable load across the cell and then measured the developed current and voltage. The circuit for this can be seen below:
Once I had recorded a decent number of point I then plotted the measured current against the developed voltage and this gave me the well known I-V curve:
It should be noted that I excited the solar cells with a 7W LED light bulb and not a calibrated 1sun source, hence what you see is not an indicator of their true performance. Still the curves show that both cells are closely matched in performance (same Voc & Jsc) and so can be easily use in series or parallel configurations. 

Solar LED Lamp Controller, CL0116

It turns out that most cheap solar powered lanterns use a specialised IC (U1, CL0116) to control the charging/discharging cycle of a rechargeable battery (BT1) which is usually a single NiMH cell. From my understanding this IC is basically a switching converter which uses and inductor (L1) to efficiently boost up the voltage and in-turn power an LED; the anode of which would be connected to the LX pin and the cathode to GND. When the IC senses the solar cell is illuminated (can produce power) it enables the charging cycle of the battery, but as soon as light is removed then it starts to discharge the battery by powering the LED.

For some reason this IC is kinda hard to source as I've only seen it available on Alibaba.
EDIT: QX5252 is an alternative part that has the same functions and is much easier to find.

Candle/Flickering LED

If you happen dine out you might have seen LED powered candles which have this neat flickering effect to imitate flame. Well the interesting thing with these candles is that they are usually composed of a single CR2032 battery and what seems to be a single LED, but if you look closer at the LED package you would notice that it also houses a separate IC which controls the flickering effect (here is a really good breakdown of how these work).

These LED's are a bit easier to find and can be sourced from your local 2$ shop or eBay.

Combining It All Together

Now putting it all together sounds like a simple task: connect the two solar cells in parallel to SBAT(1), hook up a NiMH battery to BAT(2), and replace the simple LED with a flickering one.

Sadly trying this proved to be fruitless as it appeared that the output ripple voltage of CL0116 was too great for the LED IC to handle and instead the "flickering" LED stayed a solid colour.
To solve this I tried adding a smoothing capacitor (C1) to reduce the ripple voltage but soon found that using large values (>0.5uF) would completely turn the LED off; I believe this is due to a large inrush current during start-up which in turn causes the output voltage of the converter to collapse (kinda like some switching converter IC's have a maximum output capacitance).
After much trial and error I found that a value between 10-22nF gave the best result. Interestingly choosing C1 as 10nF resulted in a lower drawn current but also increased the chance of the circuit not working when trying a different flickering LED, hence to stay on the safe side 22nF should be chosen.

By simply having D1 in parallel with C1 resulted in a drawn current of around 70mA, a bit too high for my liking as most eBay auctions state that the forward current is 20-30mA. I found that a 10Ω current limiting resistor (R1) does the trick quite well and reduces the drawn current to ~30mA at very little cost to LED brightness. Also strangely enough placing R1 after D1/C1 gave the best results in terms of current draw; I'm in the process of getting an old school analog oscilloscope so hopefully will be able to give a better answer as to why.

Finally placing it all into a 3D printed house gives you something like this:



Friday, November 20, 2015

PROJECT: Glowing Minecraft Cube

A while back it was my little brothers birthday, and since he is an avid fan of Minecraft I decided to print him a little cube from the game. The only difference with this cube was that it's internal layer was made out of glow in the dark PLA which once energised by and light source would give off a cool glow like so:


Experimenting with different coloured LED's (as the light source) I found that a blue LED gave the best results in terms of resultant glow. Thinking back to my physics classes this makes sense, as the energy (E) of any given wavelength (λ) of light is governed by the equation:


E = h⋅f 

or similarly

E = (hc)/λ


Where h is the planck constant, f is the frequency of light, c is the speed of light in vacuum, and λ is the wavelength of light.
Now if you have a look at the datasheets of a red, green, and blue LED's you would see that the wavelength of each would be roughly 625nm, 525nm, and 465nm respectively. Applying the second equation (with hc being constant) you would see that a light emitted by the blue LED has the greatest energy out of the three, and hence would be preferred choice for energising the luminescent PLA material.

With all that said I made a simple current limiting circuit to drive a blue LED at a forward current of ~220mA from x3 AA batteries, the schematic for this is below:

NOTE: The above circuit is not the best way to limit current flowing thought the LED as any variation in the supply voltage will have a relatively big effect on the forward current. Here is a much more stable current limiter, but you would need to make sure that your Rsense resistor sufficiently rated (think P=(I^2)⋅R).


All of this was then placed into a 3D printed case (which you can get here), in the end giving you something like this:





Thursday, November 19, 2015

PROJECT: 3D Printed Lithophanes


So a while back I found out that you could easily use a 3D printer to make a lithophane. For those not familiar with the term think of a solid object that varies in thickness in a particular way that it forms a picture when light in shined though it, giving you something like:


It turned out that my partners birthday was also coming up, so I decided to make a cube which held a number of pictures that would also be illuminated by an RGB LED (see previous post).

The thing that I soon found was that calibrating the printer for making these is quite a project in itself, as it must have taken me at least 20 prints (at various settings) before I could get a reproducible and working piece. But with that said here is how I did it, so that you don't have to suffer as much as I did:
  1. The very first step I'd recommend you do is calibrating your 3D printer, particularly making sure that your steps (X,Y,Z,E) and hotend temperature is within reasonable values. Thomas has a few awesome videos for this.
  2. Once you are happy with your printer download BMP2IGES, a super handy program used to make lithophane STL's.
  3. Before using BMP2IGES know this, the higher the resolution of your picture (pixels wise) the more difficult it will be to print it successfully. For example say I have a 0.4mm nozzle (use a 0.5mm extrusion width) and I want to print a 100mm by 100mm lithophane, what is the maximum resolution image that I can use? Well I found that setting the maximum "pixel" size of the lithophane at half your extrusion width gives good results. So with the 100mm by 100mm example the maximum resolution image I'd use is 400 x 400 pixels [100÷(0.5÷2)].
  4. Next grab the image you want to use and resize it appropriately. Once you've done that open up BMP2IGES and import the image by clicking File -> Open. The picture below shows the parameters that I found to work quite well. Feel free to play around with these though to see what they do.
  5. Having set all that up next create the STL by clicking File -> Save&Calculate -> Save as STL. BUT before using the STL there is a high chance that it has some errors, so use a program like netfabb to repair it (here is a good video of how to repair STL's).
  6. Now that you have your good STL file import it into your favourite slicing software (I use Simplify3D myself). First major change you need to do is make the infill solid, as we don't want your fancy infill pattern interfering with the picture. I find that with my printer making the infill rectangular with a fill percentage of 85% does the job well. Also some people say that printing your infill at a lower angle (<30°) gives better results, but I found that 45° works just fine. Lastly the slower you print the better lithophane will come out to be, for me 50mm/s gave good results. Here is pictures of my printing settings, but since optimal values differ from printer to printer it's up to you to have a play around. 
  7. Finally hit print and hope for the best ( ͡° ͜ʖ ͡°)


If you want to take this lithophane business one step further you could also make an enclosure box and place an LED in the centre to light it all up, kinda like the picture below:


You can get the model for the enclosure from here. I've also included the circuit schematic and code below. For my project I decided to use the cheap and plentiful ATtiny13 (which I programmed via my Arduino UNO with the help of this tutorial), but you can use any AVR micro you want as long as it has x3 PWM outputs, x1 analog input, and x1 digital input.

NOTE: I found that limiting the forward current to ~220mA gives the best compromise between brightness and heat produced. 

/////////////////////////////////////////////////////////////////////////////////////////////
// RGB LED control - v1.2                                                                  //
//                                                                                         //
// A simple program for controlling an RGB led with a single potentiometer.                //
// As per I/O pins below, the RED pin of the RGB LED is connected to pin #9 of the Arduino //
// GREEN pin to pin #10, and BLUE pin to pin #11. Also the output of the potentiomenter is //
// located on pin #A0.                                                                     //
//                                                                                         //
// ANTALIFE - 16.08.15                                                                     //
/////////////////////////////////////////////////////////////////////////////////////////////

//MUH I/O PINS
int R_pin       = 1;  //9  on Arduino
int G_pin       = 0;  //10 on Arduino
int B_pin       = 4;  //11 on Arduino
int RGB_pot_pin = 3;  //A0 on Arduino
int Rainbow_pin = 2;  //8  on Arduino


//MUH VARIABLES
float theta       = 0;
int colour        = 0;
int rainbow_delay = 0;

void setup()
{
  //MUH OUTPUTS
  pinMode(R_pin, OUTPUT);
  pinMode(G_pin, OUTPUT);
  pinMode(B_pin, OUTPUT);
  pinMode(Rainbow_pin, INPUT);
}


void loop()
{
  //If rainbow mode enabled scroll through the rainbow ;^)
  while (digitalRead(Rainbow_pin) == LOW)
  {
    for (float RAINBOW = 0; RAINBOW < 256; RAINBOW = RAINBOW + 0.5)
    {
      //If rainbow mode disabled stop animation
      if (digitalRead(Rainbow_pin) == HIGH)
      {
        break;
      }
      MUH_colour(RAINBOW);
      delay(analogRead(RGB_pot_pin) + rainbow_delay);
    }
  }
  
  //If rainbow mode not enabled simply display the set colour
  theta = analogRead(RGB_pot_pin) / 4;
  MUH_colour(theta);
}

void MUH_colour(int angle)
{
  //This fucntion converts the given angle to a visible colour on the colour wheel
  //with RED being 0deg, GREEN being 120deg, and BLUE being 240deg
  //RED TO GREEN [0deg -> 120deg OR 0 -> 85]
  colour = (6 * angle) % 255;
  if (angle <= 42.5)
  {
    RGB_write(255, colour, 0);
  }
  else if ((angle > 42.5) && (angle < 85))
  {
    RGB_write((255 - colour), 255, 0);
  }
  //GREEN TO BLUE [120deg -> 240deg OR 85 -> 170]
  else if ((angle > 85) && (angle < 127.5))
  {
    RGB_write(0, 255, colour);
  }
  else if ((angle > 127.5) && (angle < 170))
  {
    RGB_write(0, (255 - colour), 255);
  }
  //BLUE TO RED [240deg -> 360deg(or 0deg) OR 170 -> 255(or 0)]
  else if ((angle > 170) && (angle < 212.5))
  {
    RGB_write(colour, 0, 255);
  }
  else if ((angle > 212.5) && (angle < 255))
  {
    RGB_write(255, 0, (255 - colour));
  }
}

void RGB_write(int R_val, int G_val, int B_val)
{
  //A simple function that displays the desired LED colour by setting the duty of the
  //PWM on each RGB LED
  analogWrite(R_pin, R_val);
  analogWrite(G_pin, G_val);
  analogWrite(B_pin, B_val);
}

And finally here is a video of it all working :D




Sunday, August 9, 2015

ARDUINO: Controlling an RGB LED with a potentiometer


One of my upcoming projects will require me to control an RGB LED with a single potentiometer.
Scouting the internet for relevant code came out a tad fruitless as most code had poor transitions between each RGB value, as you could see each LED momentarily turning OFF between major transitions.

So after having a look how an RGB colour wheel works (http://www.colorspire.com/rgb-color-wheel/) I decided to write a simple function myself, thus giving the code below:
/////////////////////////////////////////////////////////////////////////////////////////////
// RGB LED control - v1.1                                                                  //
//                                                                                         //
// A simple program for controlling an RGB led with a single potentiometer.                //
// As per I/O pins below, the RED pin of the RGB LED is connected to pin #9 of the Arduino //
// GREEN pin to pin #10, and BLUE pin to pin #11. Also the output of the potentiomenter is //
// located on pin #A0.                                                                     //
//                                                                                         //
// ANTALIFE - 09.08.15                                                                     //
/////////////////////////////////////////////////////////////////////////////////////////////          

//MUH I/O PINS
int R_pin       = 9;
int G_pin       = 10; 
int B_pin       = 11;
int RGB_pot_pin = 0;

//MUH VARIABLES
int anal_val    = 0; // ;^)
int theta       = 0; 
int colour      = 0;

void setup()
{
  //MUH OUTPUTS
  pinMode(R_pin, OUTPUT);
  pinMode(G_pin, OUTPUT);   
  pinMode(B_pin, OUTPUT); 
}


void loop()
{
  //Using an RGB circle with RED being 0deg, GREEN being 120deg, and BLUE being 240deg
  //Here we map the 360deg circle to a value between 0 and 255 (aka the duty of the PWM)
  theta           = analogRead(RGB_pot_pin)/4;
  colour          = (6*theta)%255;
  
  //RED TO GREEN [0deg -> 120deg OR 0 -> 85]
  if (theta <= 42.5)
  {
    RGB_write(255,colour,0);
  }
  else if ((theta > 42.5) && (theta < 85))
  {
    RGB_write((255-colour),255,0);
  }
  //GREEN TO BLUE [120deg -> 240deg OR 85 -> 170]
  else if ((theta > 85) && (theta < 127.5))
  {
    RGB_write(0,255,colour);
  }
  else if ((theta > 127.5) && (theta < 170))
  {
    RGB_write(0,(255-colour),255);
  }
  //BLUE TO RED [240deg -> 360deg(or 0deg) OR 170 -> 255(or 0)]
  else if ((theta > 170) && (theta < 212.5))
  {
    RGB_write(colour,0,255);
  }
  else if ((theta > 212.5) && (theta < 255))
  {
    RGB_write(255,0,(255-colour));
  }
}


void RGB_write(int R_val, int G_val, int B_val)
{
  //A simple function that displays the desired LED colour by setting the duty of the
  //PWM on each RGB LED
  analogWrite(R_pin, R_val); 
  analogWrite(G_pin, G_val);
  analogWrite(B_pin, B_val);
}


To give a quick explanation of the code look at the picture below. You see how as you move around the colour wheel (or change the theta angle) the R G B values of the LED change accordingly giving you a certain colour. One other thing to note is that only two values are being changed at any given point, that is from 0deg to 120deg only the R and G values change while B stays constant (you can witness this by playing around with the colour wheel link above).
Knowing all this the above code maps the angle theta to a certain mixture of PWM duty on each LED, in the end giving you a pretty display of colours.


EDIT: Turns out humans see the brightness of colours differently, here is a good post about how this would have to be accounted for in software.

Just a simple blog for somewhat simple projects of mine.