If you want a small and shiny finalkey like this you have to move some components from arduino micro pro
or you have to move light from one place to another.
 Lets see how this is done for the Red Heart.
During the process you have several chances to brick your arduino.
Be careful and patient and you will succeed.

Red Heart : a shiny finalkey with a small form factor

finalkey : red heart

Parts used :

finalkey : red heart - parts used
  1. arduino micro pro
  2. brass rod, 1mm thick, about 12 cm long
  3. 24LC512 EEPROM
  4. 2 x 4,7 kOhm
  5. 2 x strips acrylic, 1 to 2 mm diameter and 10 mm length ( to send light from green and yellow led to surface)
  6. tinfoil (1 square cm  will give you lots of reflectors to direct light from led to surface)
  7. red smd led (finalkey led)
  8. green smd led (power led)
  9. 2 x smd resistor (160-220 Ohm for red, 220 to 500 Ohm for green, both set led current)
  10. One red or one transparent heart shaped gemstone, flat (1-2 mm thick), 6 to 10 mm diameter ( to cover red finalkey led and make it even more shiny)
  11. One green or one white/transparent gemstone for power led (flat, 1-2 mm thick)
  12. large pushbutton (finalkey button)
  13. 2 single strips of a stripboardboard (to set up red finalkey led and green power led)

Additional stuff


Technical Problem: 2 leds at the bottom?

I wanted to get a small form factor and a large shiny red finalkey light.
As the input and output  led are at the bottom of this design
i have to move the light from the power led to some other place.
An easier way to do this is to use some acrylic drop offs.


Check functionality after each step is done! If you discover any serious error after step 6 you have shiny brick :(

1. finalkey basic setup : programm arduino micro pro, solder Button and two 4.7 kOhm resistors
2. Bend brass rod and glue it around the arduino micro pro board.
3. Prepare finalkey-led and power led with mini circuit boards.
4. Glue LED-stripboards to arduino mini pro and connect them.
5. Glue gemstone on red Finalkey-LED and power-LED.
6. Glue 2 acrylic poles onto green and yello led of arduino micro board.
7. Cover your creation in repair glue.
8. Sand it, color it, varnish it.

1. finalkey basic setup

       program finalkey software or -> see dusteds setup,
       solder eeprom to arduino board
       solder big pushbutton to arduino board
       solder 2 x 4.7 kOhm,

2. bend brass rod and glue it around the arduino micro pro board :

finalkey back with resistors and brass rod

You might consider to attach the brass rod before soldering the basic parts for finalkey. But chances are high that glue will go into mounting holes at the side of the arduino board. If this happens, you have a big problem. So you better solder basic stuff first, glue rod afterwards.

Cut about 12 cm from a brass rod of 1mm diameter.
Make it longer if you want to hold with your finger.
Brass rod (1mm) is easy to bend and strong enogh to make a proper handle. Thinner brass rod is too soft. Thicker brass rod is very hard to bend. Aluminium is too soft. Anything with  plain iron will rust. High quality steel is too hard. Silver is too soft. Go for gold alloy, used for tooth crown, if you have the money. Its even shinier than brass ;-)
Dremel or sand the edges of arduino pro to get "round" soft edges at the usb side of the board.
It is close to impossible to bend the rod to a 90° angle. Its always a bit round at the edge. As you will want a close fit you have to get rid of the sharp edges at the usb port side of the circuit board.
This is not a problem on the other side (not usb ...). There is no 90 degree angle for the brass rod.
Bend 3-5 mm as tight and close to 90 degrees for the usb side as possible
If you sanded the edges properly, the rod will have a tight fit which is essitial for handling the board afterwards. These bended parts of the rod take the load for any drag on the opposite side. If you dont have tthem the glue at the sides of the board has to take the load alone. This is not prefereable.
Bend it to a curve on the other side with a distance of 1-2 cm from the board
If you need a large curved rod to even put your finger through it, make it larger. I only want it to hang an a hook or to attach it to a key ring.
Bend it as tight and close to 90 degrees as possible for the other edge close to usb.
Cut off  the part which does not fit :).
              brass rod bended, ready for test
see 2.2
Its no problem if the rod just slightly touches the usb port as it is grounded. But the rod should not move away from the board because the bent part is too long. Remember : a tight fit is the goal.
If you bend it just a little too much inwards it will cling to your board by itself (see image in the left). Gluing will be easy then. If you don't have a tight fit, you will have a hard time fixing the rod when you try to glue it to arduino.
Make sure to have a flat construction that fits exactly around the circuit board :
              brass rod, check
If your construction is not flat you will not be able to glue it around the circuit board. Instead you will be ruining your fingers, the circuit board, your clothes and anything close to your handling area in the attempt to get it done. A simple test : lift your arduino board wihout touching the rod. If the rod sticks to the board without moving you are ready to go for the glue.
Glue it around the board and let it cure. Make sure that it does not touch any wires/conducting parts.
You will have a nice handle now for all the steps following.
              back with resistors and brass ro attached
I always use a strong 24 hour curing 2 component glue to make sure that i get a strong and durable connection. Dont use super glue or any stuff which goes hard like a crystal after curing. Its not very usefull for parts with large gaps. And dont use anything soft like regular paper glue. It will not even hold the circuit board alone if bad luck hits you. Hot glue might be an alternative if you have a gluegun with a very fine tip. Otherwise you will find glue all over the place. And its not as strong as i want the bonding to be.

If you dont attach this handle all coloring and varnishing actions will be a pain. And you can't put your key on a chain or necklace.

3. prepare finalkey-led and power-led with a mini circuit board

Cut off a single line stripboard, seven holes long.

one line from stripboard
This line will fit onto the arduino micro pro board.
Any stripboard with 2.54 mm distance between holes will do it. Otherwise you have to recalculate length. Anyway, only one hole has to fit exactly : +5V. The other end will be connected by a wire, so there does not have to be an exact match of holes at the ends of our mini-led-board with the arduino board.
Cut the copper line at 2 holes, one exactly in the middle, thats where the led goes.
cuts in led stripboard
The two cuts are the mounting places for a resistor and the led. The resistor has to have a minimum of 160 Ohm.
Red LEDs needs about 1.8 Volt at 20 mA. As we are running our finalkey from usb port, 5 Volt will kill it without a resistor taking the voltage up to 5 Volt.
R=U/I -> R= 3.2Volt / 0.02 mA -> R=U/I=160. Depending on your LED and its brighness you can go up to several hundred Ohm and it will still be bright. Nowadays LEDs might blind you if you run them with maximum allowed current.
Solder resistor and led over cuts, test it at 5 Volts ! Resolder if necessary.
Kathode (GND) goes to Pin 10 of arduino for your FinlKey LED.

mounted resistor and led on

I used a 180 Ohm resistor which protects the red led and still allows enough current to make it shine bright.
Dont connect it to arduino yet.
NO GLUE, NO SOLDERING to arduino. You have to glue fiber optics to red power led first. This is located to some extent below the finalkey led stripboard.
See image 4.4.
Attention reset button users :
If you want a reset button you better solder the resistor to the right and cut off 2 holes from the stripboard on the left. You will need this space for the reset button

Build another one with a green LED for power-LED.
Anode goes to +5V/VCC. Kathode/GND goes to GND.

Test both strips before soldering them onto your arduino.
 Available connectors on your arduino board :

arduino pro
              micro GND and VCC connectors

4. Glue LED-stripboards to arduino mini pro and connect them.

FinalKey Red Heart, leds soldered side view
Led-stripboards soldered, side-view. The image is taken from the Green Miracle. Stripboards are sanded to a minimum. If you dont sand them the stripboards will raise LEDs and gemstones.
Make sure not to short anything by leaving a clear gap between arduino board and your wires (1)

Glue both strips to arduino. Test both before soldering.
You can place them on your board so that at least one hole matches with arduino. Or you can place them wherever you like and use 4 wires to connect them. I recommend to use at least one matching hole : FinalKey-led and VCC(+5V). Keep in mind that you need some room for the big FinalKey-led-gemstone. It sits in the middle between button and power LED in my setup.
Solder LED connections to arduino. Finalkey-LED needs +5V/VCC, Kathode goes to pin 10 (needs a wire, the white one in the image above)!
Power LED needs +5V and GND (some short wires like cut off led wires will do it)

5. Glue gemstone on red FinalKey LED and power-LED and let it cure.

Use fast curing 2-component glue or be prepared to hold it in place for 24 hours.
If you use a heart-shaped gemstone like i did think about its orientation.
If it will be worn on a necklace the tip of the heart should probably point to the usb-port (i.e.down).
In my setup it points towards the button and brass rod.

6. Glue two acrylic poles as light pipes onto green and yellow led of arduino micro board

FinalKey with
        acrylic pole as mirror on io-led

arduino pro micro with one of the two lightpipes mounted :
1 : acrylic pole sends light from led to surface, it works as light pipe.
2: aluminium foil mirrors light into your light pipe.

Cut some acrylic of a thin sheet 1x1mm up to 2x2mm, 1cm long (see image above)
This tiny pole will act as a light pipe and guide light from an led to the surface of your FinalKey. The smaller its cross section is the better it will work. See your old physics book at : total internal reflection. The bigger your cross section gets the more light will escape.
Cut one end at an angle of about 45°
This end will act as a mirror. It will sit exactly above the led.
If you want to make it perfect, polish all sides. The smoother the surface the more light will stay inside your light pipe.
Glue a small square of aluminium foil onto the 45 angle part (see image at 2).
Or put a long strip of foil on the upper part of your light pipe. Dont cover the whole pipe because you are most likely creating a short when you glue this on your board.
This is the mirror ... it will reflect light from the LED into your light pipe.
Glue your mirror on top of the led (see below, 6.4, and the image above)
Put the aluminium exactly above the led. If you miss the LED most of its light will escape.
If you want even more light put some more aluminium on top of your pipe and at its side. Dont put anything below. Chances are high that you short some contacts and brick your arduino. If you put aluminium on the sides be carefull to only cover the upper part and dont come close to the bottom -> avoid short circuits on arduino!
Mount another light pipe on top of the second LED.
Cover both with aluminium foil without any contact to components on your board.
finalkey board with two mounted
                acrylic light pipes on IO-LEDS
Its ok to have too long light pipes. They will be cut off after you covered your board with repair glue. If you have too short light pipes it will be a pain to find them afterwards. The repair glue will be in line with the button edge. In the picture on the left i had to remove about 1 to 2mm.
Let it cure

7. Cover your creation in repair glue. (See green miracle)

8. Sand it, color it, varnish it.

If you know your repair glue you can just cut off stuff while its curing. Sanding should be done only when its really cured after about a day. Start with medium grade sanding paper (180). This works for almost 90% of your work. Only at the very end you might use very fine grades (400).
If you dont want to color and varnish it try to get a very smooth surface. It will not collect any dirt then.
If you varnish it, you dont have to be very picky about a smooth surface. Small screatches will be filled and cleared by the varnish.

Color and Varnish:

To be on the safe side put a cover on top of the switch first. Cut some plastic sheet and glue it to the edges of the button. Be careful not to come close to the button itself.  If you use some soft glue then varnish and color stains can be removed easily by removing the plastic. Always keep the usb connector down. If you dont you might mess up the usb port. You can cover this too if you want to. If you are carefull you dont need to cover it.

If you go for a coloured version without glitter use nail varnish. You get it reasonably priced from a dollar- or euro-store. Nail varnish comes in a large variety of colors in small quantities for little money. If you have to pay more than a euro for a small bottle its a rip-off. If you go for heavy duty usage buy some spar varnish used for boats and tint it with a color of your choice. This will be expensive. I did not test acrylic paint. It might work for you. Test it on your repair glue before you use it!

Let it cure for about an hour before you apply another layer depending on your brand of varnish. If you are impatient you will just smear and uncover parts which you considered done.

Put a final layer of clear top coat varnish on to make it even shinier. Depending on the kind of varnish you use a single layer might be satisfying. I always had to use several layers to get the color and surface i wanted.

              (thunderchild), logo

Design and hardware extensions used for
Red Heart, Alien Artefact and Green Miracle :
tc (thunderchild), Nov 2014

All praise and credit for FinalKey hardware and software go to dusted.