Tuesday, October 7, 2014

Retrobright your R2-D2

Yellowed R2-D2?

This R2 unit was acquired from some jawas who came by my house a long time ago...

So long ago, that its shell yellowed from the effects of the UV and its 12+ years of ownership.

This is the Hasbro voice command R2 unit, made of plastic..

Since the yellowing is caused primarily by the bromine present in the flame retardant the manufacturer adds to the ABS plastic, I thought of actually reversing the yellowing process instead of painting R2.

This can be accomplished with a mix called Retr0bright.

These are the preliminary results after day 1:

Left: 10:30am.   Right: 6:00pm after brushing it with Retrobright and direct UV from sunlight.

The results are impressive to say the least. The yellowing does not go away completely but I am very satisfied with the improvement. Texture of the plastic was not affected in any way, although the blue paint got some stains that I think I can fix with polishing with some cloth.

Skills required:

- Disassembly skills and (screwdrivers+patience). There's an instructive video on how to disassemble R2.

- Soldering skills. Quite a bit, yes. In order to truly separate all the plastic from electronics, you need to de-solder some of the wiring. And you want to truly separate plastic because you will need washing, brushing, painting, rinsing your droid. Attempting this on an assembled model will be MUCH harder.

Inside R2.

Detail of motor circuit being de-soldered.

Ultra-Violet (UV) exposure for 7 hours

Get it done:

1.- Check the weather forecast and ensure a full sunny day if that is possible at your location.
2.- Lay your plastic parts as separate to each other as you can, so they don't shadow themselves.
3.- Put on your gloves and goggles and prepare a Retr0brite mix. 1/3 of a cereal bowl should do. It will seem too much at first but you will be re-applying many times throughout the day until you deplete your dose.
4.- Paint a layer over the yellow. Try to avoid paint and stickers but if you paint over them there won't be substantial damage to the paint so no need to be perfect.
5.- Leave it there for two hours and re-apply as soon as you see it's drying out. Rinse your latex gloves with water every time, then remove them from your hands.
6.- Let the sun do its magic.
7.- Go to step 5 until sunset.
8.- Rinse your plastic parts one by one and use a brush to ensure mechanical removal. Don't ever remove your gloves nor your goggles.
9.- Repeat another day if needed. 
10.- Sell it to the same Jawas for double the price.  


This project is not for kids. Maybe not even for adults (if you happen to have another droid to do this for you, have HIM do it.)

The reason being that Hydrogen Peroxide at this concentration can SEVERELY BURN YOUR SKIN or BLIND YOU FOR GOOD.

I used latex gloves at all times, and while rinsing the plastic with a brush I accidentally sprayed some of the substance straight to my eyes. I was wearing eye protection, however I experienced some burning on my face out of oxidative stress on skin, to a point it hurts and whitened the surface of the skin.


Sunday, April 13, 2014

Lower the volume on your Fluke Multimeter in two minutes (literally).

Industrial multimeters are not designed for your quiet and peaceful electronics lab. They are designed for industrial, loud environments.

That said, testing continuity with a Fluke 87V at an electronics workbench can be quite annoying, reason why I decided to lower its volume a little using a simple, quick and reversible method.

Adding a 4.7k Ohm resistor in series with the buzzer will do the trick, setting your volume at a pleasant level.

Open your DMM and this is what you will find: The piezo buzzer contacts the board with springs to these pads shown here:

What you will see now is the back cover, where the buzzer lives. The two springs at the bottom are (-) and the one at the top is (+).
Just fold the leg of your resistor around the (+) spring and raise the other leg RIGHT ON TOP of the spring like this:

Then isolate both the resistor AND the spring with tape. I used Kapton tape as seen here:

Make your final adjustments so the resistor led lays right on top of the little spring. This leg will make final contact with the pad on the main board of your DMM.

Add another tape to on top of the larger portion of the resistor leg and leave the tip uncovered.

Close the cover gently and test your meter.

Done!  If you are fast with your screwdriver, this literally takes two minutes. But take your time...
Best of all, this is 100% reversible, with no permanent modifications to your DMM.

Note: You may have noticed that some photos show 10K resistor while other photos show 4.7K. That's because I started with 10K but then realized volume was too low. 4.7K seems to be perfect for my needs.

Friday, March 28, 2014

Quick LED tester for your Protoshield

Why build this project:

1) Because it's an LED tester on your proto shield that doesn't mind orientation. Ideal for quickly testing a suspicious LED or checking the color on a transparent LED.

2) Arduino independent, it's based in the 555 bi-polar LED driver, so it doesn't interfere with any of your Arduino pins or code.

3) Because it's easy and affordable way of learning how a 555 works.

How to build this project:

It goes like this:

Use this build as a learning experience on the 555!

What happens at the LED side?

Look at the diagram above. Let's imagine you have two LEDs, one GREEN, one RED connected just as above. Commonly referred to as Vcc, the supply voltage can range between 5V and 15V. In this example, we will use 9V.

1) Simply put, we are connecting the left leg of the LED to the output pin (3), which oscillates between 0V and the supply voltage (Well, actually the supply voltage minus 1.7V so it's around 7.3V in this case. Refer to the 555 timer wikipedia article for details.)

2) The other leg of your LED (the one on the right) is connected to the resistor divider, which divides the 9V. So only 4.5V are present at that leg.

3) As a consequence of step 2 above, when pin (3) his HIGH, your LED sees a potential difference of 4.5V, and when (3) is LOW, it sees a potential difference of -4.5V and BAM! That's why the current alternates in both directions allowing you to place LEDs in any orientation.

Note: Since I usually feed my Arduinos with 12V, I replaced the two 220 Ohm resistors for 290 Ohm in order to reduce the power consumption of the resistor divider to less than 1/4W. This impacts consumption but the voltage divider still divides to 4.5V.

OK, got it. Now, what happens at the capacitor/resistor side?

1) The combination of the Cap and the resistor produces a delayed charge and discharge of the capacitor. The very same output pin (3) we use to drive the LED is used here to both charge the capacitor when output is HIGH and discharge it when the output is LOW.

2) Both inputs of the 555 Trigger (Pin2) and Threshold (Pin 6) are shorted together, which leaves us with a single input that reads the voltage at the capacitor.

3) Remeber that in this example we are feeding the circuit with 9V. Whenever the input reads below 3V from the capacitor, it will turn the output HIGH, turning the green LED ON. At the same time, the capacitor begins to charge, slowly rising the voltage at the input pin (2 and 6).

4) As soon as this rising voltage gets above 6V, it will reset the 555, setting the output to LOW which activates the red LED, and at the same time it begins to discharge the capacitor, which will eventually get to below 3V, leaving us at step 3 again.

So, why are these boundaries at 3 and 6 volts?

Because I used 9V as an example for feeding the circuit. 3V and 6V are 1/3 and 2/3 of 9V respectively.
If I had used 12V to feed my circuit, boundaries would have been 4V and 8V respectively because it's always 1/3 and 2/3 of the supplied voltage.

Can I make them blink quicker or slower?

Of course you can. Check out these great resources:

1.- HyperPhysics at Georgia State University - A simple tool for calculating time to charge/discharge your capacitor.
2.- Wikipedia - RC time constant

Top view:

Bottom view:

Can I see it working? 

Yes, you can. Check the video I made for you:

Finally, if you want to see some of my other mods for the Proto Shield, click here.

Friday, February 28, 2014

Moody Tubes - Vacuum tubes to set your mood!

This is an ornament made of old vacuum tubes and some basic electronics including LEDs, Arduino and resistors.


- Three tubes which slowly change colors.
- Integrated battery meter. Right after power up, it measures its own battery level and shows the level by graduating one of the tubes from Green(full) to Red(needs recharging). If at any point battery goes below threshold levels, it will go into "blink-red" mode and will refuse to do its coloring thing.
- Potentiometer for manual adjustments.
- A battery. I used a Lipo 11.1, 2500mAh battery which was almost gone for trash because it couldn't serve my airplanes anymore.

Materials required:

- A suitable box
- Vacuum tubes (don't need to be in working condition, just need to look pretty)
- RGB LEDs (One per tube)
- 330ohm resistors (15 of them or a resistor array as I used)
- Your favorite micro-controller (I went for an ATMEL Atmega 328).
- A 5v regulator
- A potentiometer (may be even buttons or an IR sensor)

Plan for it

Assemble the hardware. 

Leds are hot glued underneath the tubes:

Consider from my design that the three LEDs are in parallel, which means they show the exact same color at all times. The only one that's different is the center one, where I added an orange led for a cleaner orange tone.

Also consider that LEDs can be turned ON or OFF independently, reason why instead of a common ground connection they go to digital output pins. This also means that to power up each LED you need to bring that ground pin to LOW.

Let's take a closer look at the power regulator:

Pick your colors.

I wrote some code to manually change each color so I could visualize the mix I liked the best, and wrote those values down.

Enjoy your relaxing toy.

Use the potentiometer to increase or decrease the speed at which colors change. I went from somewhat fast all the way down to super-super slow. It will take several minutes to change to the next color. This is for a more realistic approach.

Arduino Code

int redPin = 9;
int greenPin = 10;
int bluePin = 11;
int orangePin = 6;
int tubesmaPin =5;
int tubelarPin = 4;
int tubemedPin = 3;
int potPin = A2;
int buttonPin = 7;
int battPin = A1;
int maxbattery = 283;  // reading at which the battery is at 12.3V, which we consider full capaciity.
int minbattery = 244;  // reading at which the battery is at 10.8V, level at which we will consider the battery needs urgent recharging.
int boot_check = 1;
long previousMillis = 0;        // will store last time LED was updated
int redvalue = 0;  // Stores the current value of the color
int greenvalue = 0;
int bluevalue = 0;
int orangevalue = 0;
int potenciometro;
int transitfinished =0;
// __________________________________________________________________________________________________________________________________________________________________
void setup()
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
  pinMode(orangePin, OUTPUT);
  pinMode(tubesmaPin, OUTPUT);
  pinMode(tubelarPin, OUTPUT);
  pinMode(tubemedPin, OUTPUT);
  pinMode(potPin, INPUT);
  pinMode(buttonPin, INPUT);
// __________________________________________________________________________________________________________________________________________________________________
void loop()
  //while(digitalRead(buttonPin)) { go_manual(); }
  //delay(1000); // delay after the press of the button
  //while (digitalRead(buttonPin)){ go_automatic();}
// __________________________________________________________________________________________________________________________________________________________________
// __________________________________________________________________________________________________________________________________________________________________
System health functions
// __________________________________________________________________________________________________________________________________________________________________
void check_voltage() // blinks one tube with the status of the battery: Green = 12.4v, Red is below 11.1v and needs recharging
  int battvalue = 0; // stores the reading on the battery
  battvalue = analogRead(battPin);
  battvalue = map(battvalue,minbattery,maxbattery,0,255);
  if (battvalue<0) battvalue = 0;
  if (battvalue>255) battvalue = 255;
  if (battvalue<1) show_dead_battery();
  if (boot_check == 1)  //Does this only once when booting.
      // green = full, red = depleted.
      digitalWrite(tubesmaPin,LOW); // Activates the small tube
      digitalWrite(tubesmaPin,HIGH); // Shuts the tube down
      boot_check = 0;
// __________________________________________________________________________________________________________________________________________________________________
void show_dead_battery()  // Breathes red tube FOR EVER, nothing else.
  shutdown_tubes(); // Shuts all the tubes down
  digitalWrite(tubesmaPin,LOW); // Activates the small tube by bringing the cathode LOW.
  int destination = 255;
      if (redvalue==0) destination = 255;
      if (redvalue==255) destination = 0;
// __________________________________________________________________________________________________________________________________________________________________
Functions involving LED activity
// __________________________________________________________________________________________________________________________________________________________________
void setColor(int red, int green, int blue, int orange)
  analogWrite(redPin, red);
  analogWrite(greenPin, green);
  analogWrite(bluePin, blue);
  analogWrite(orangePin, orange);
  // let's reflect the current values in the variables
// __________________________________________________________________________________________________________________________________________________________________
void transit_color(int transitspeed, int red, int green, int blue, int orange)
  unsigned long currentMillis = millis();
  if((currentMillis - previousMillis) > transitspeed) //If transitspeed = 12 implies approx 3 sec in raising a led from 0 to 255
        // save the last time I adjusted the LEDs
        previousMillis = currentMillis;
        if (redvalue<red) redvalue++;
        if (redvalue>red) redvalue--;
        if (greenvalue<green) greenvalue++;
        if (greenvalue>green) greenvalue--;
        if (bluevalue<blue) bluevalue++;
        if (bluevalue>blue) bluevalue--;
        if (orangevalue<orange) orangevalue++;
        if (orangevalue>orange) orangevalue--;
        if (redvalue==red && greenvalue==green && bluevalue==blue && orangevalue==orange) transitfinished = 1;
// __________________________________________________________________________________________________________________________________________________________________
void shutdown_tubes() // Shuts the tubes to dark by raising the cathode to high so no current flows regardles of the RGB pins
Blinking and Color Routines
// __________________________________________________________________________________________________________________________________________________________________
void go_automatic()
// __________________________________________________________________________________________________________________________________________________________________
void go_manual()
      potenciometro = analogRead(potPin);
      redvalue = map(potenciometro, 0, 1023, 0, 255);
      setColor(redvalue, greenvalue, bluevalue, orangevalue);
      potenciometro = analogRead(potPin);
      greenvalue = map(potenciometro, 0, 1023, 0, 255);
      setColor(redvalue, greenvalue, bluevalue, orangevalue);
      potenciometro = analogRead(potPin);
      bluevalue = map(potenciometro, 0, 1023, 0, 255);
      setColor(redvalue, greenvalue, bluevalue, orangevalue);
      potenciometro = analogRead(potPin);
      orangevalue = map(potenciometro, 0, 1023, 0, 255);
      setColor(redvalue, greenvalue, bluevalue, orangevalue);
// __________________________________________________________________________________________________________________________________________________________________
void breathe(int red, int green, int blue, int orange)
  while (transitfinished==0)
    potenciometro = analogRead(potPin);
    potenciometro = map(potenciometro,0,1023,6000,10); // Sets the transition speed with the potentiometer
// __________________________________________________________________________________________________________________________________________________________________