Blinken Button for Beginners Kit – How To

Introduction

Congratulation. you are probably a proud owner of a Blinken Button for Beginners Kit! This kit is intended as a beginners SMT kit – and hence the name – to learn to solder those nifty SMT parts. If you don’t already have one, head over to the shop an get a Blinken Buttons for Beginners Kit.

Before you begin check the SMT Soldering Tutorial for some first impressions what you need and how it is done. After that it is time to collect all the needed tools:

  • A soldering iron, preferably with a pencil shaped tip – it does not need to be a small tip, if it is a bit larger than the 1206 pads on the PCB (I used one, with about twice the size of the pads), it is a myth that you need a small tip for SMT.
  • Some solder, preferably with a small diameter of about 0.5mm. This gives a very good control how much solder is put on a pad.
  • Some flux, e.g. a flux pen. There is never too much flux in SMT – this is one of the things that really helps you with the difficult problems.
  • Some solder wick to remove solder from the boards & pins.
  • SMT tweezers to hold the parts while soldering.
  • A third hand to hold everything in place.
  • A wire cutter.
  • A CR2032 battery to power the Blinken Button.

Schematics

Before we begin let’s take a look at the schematic of the kit:

It is a extremely straight forward AVR ATmega168 based LED matrix button. There is a battery, connected to a switch and some capacitors for a smoother power supply. IC1 is the ATmega168 microprocessor, with a ISP header. The LED matrix is driven by the transistors T1 to T8, sinking the row current. The column current is directly provided by the ATmega168. Due to the internal over current protection of the ATmega and the high internal resistance of the coin cell battery there is no need for current limiting resistors for the LEDs. The resistors R1 to R8 limit the base current of the transistors, R9 is the pull up resistor for the reset line of the ATmega.

That’s all.

Kit Content

All of the parts, mentioned above are contained in the kit (if not, drop me a note):

  • Blinken Button for Beginners PCB
  • IC1 – Atmega168 CPU (preprogrammed
  • 8×8 LED Dot Matrix Display
  • C1, C2 – 4,7µF capacitor brownish, normally in a clear packaging, 1206 packaging
  • R1 – R8 – 470 Ohm resistors, marked 4700, 1206 packaging
  • R9 – 10k Ohm Resistor, marked 1002, 1206 packaging
  • T1 – T8 – MBT2222 PNP Transistors, SOT23 packaging
  • SW1 – switch, Copal CSS-1210TB
  • Battery holder for CR2032 battery (not included)
  • some machined sockets for the ISP programming port and to socket the display, if you like
  • some machined headers as adapters for the ISP programming port
  • some traditional square header pins for the ISP programming port (can be installed alternatively, but reduce wearability)
  • safety pin, to attach the button to your clothing

Soldering the Kit

1. Soldering IC1 – the microcontroller

First of all solder the ATmega microcontroller. This is the hardest part, since it got quite a fine pitch. But do not be scared. Solder wick and the flux pen are your freinds and will get this job done very easily!. First check the orientation of IC1. The dot on the ATmega must align with the dot and the corner on the PCB:

Next at a tiny bit of solder to one pin. It should be just one pin, but as long as you can heat all the solder with your iron it is OK. If not remove some solder with the wick. Next you should fix the ATmega on that pin. Add some flux an reheat the solder and carefully shift the ATmega into position. Check, recheck and check again that the pins align perfectly with the pads. If not, add some flux, reheat the solder and adjust the alignment of the ATmega168. In the end it must look like this:

You can see, that I accidentally soldered two pins instead of just one – it is not critical. The only critical thing is to align the pins perfectly.

After you have finished this you solder the rest of the pins. It is easier if you fix another pin on the opposite side of the ATmega168. carefully solder all pins. Do not try to solder them individually, try to solder one side of the chip at a time, trying to make not too much solder bridges. If you have some bridges, compare it with my result to be relieved, it is a complete mess:

Add a good amount of flux to rework the solder joints. Clean the tip of your soldering iron carefully. You already got all the solder you need on the PCB, perhaps even to much. Small solder imperfections, like on the left side of the chip, can be removed by heating one or two pins on the same time and dragging the soldering iron away from the chip. Allways clean your soldering tip after each drag. by that some amount of solder stays on the iron, until you removed the bridge. For bigger solder blobs, like on the right side of the chip, simply remove the solder with some soldering wick. You should try to apply not too much heat to the chip, work quickly and make enough breaks to let the chip cool down a bit. with a bit of work you get a nice and cleanly soldered chip (yes it is the same chip as above):

Congratulate yourself! This was the hardest part. No or some fun soldering.

2. Soldering the capacitors, resistors & transistors

First begin with C1 and C2 – the two ceramic capacitors. The process is really easy and explained with C1. Add a bit of solder to one of the pads:

In the next step reheat it and shift – with your tweezers – C1 into position:

Ensure that the part lays flat on the PCB. To correct this press it slightly down with your tweezers and reheat the soldering joint. Do not press to heavy – you can damage the part. If you do it carefully everthing works quite easy.

Now solder the second pad of the part:

If there is not enough solder on the first pad, simply add some, after you have soldered the second pad. With this method we work our way through the whole PCB:

Solder C2 (since you allready opened the capacitor strip):

While we are in that area solder R9 (10k Ohms, marked as 1002):

Soldering the rest of the components works in the same way and in the mean time it should be quite easy for you. Start in the top row with transistor T4. It is a good idea to solder a SMT board from the inside to the outside. This is the easiest way to ensure that already soldered parts do not block your working area. Even though the transistor T4 has 3 pins it is done in the same way. Add some solder to one of the pins, preferably the single pin on the top side. Reheat the solder, shift the part into position, ensure that it lays flat on the PCB:

Now solder the rest of the pins:

In the same way we go on with R4:

And R1:

And T1:

Move over to T2:

And finally R2:

Congratulations, you have finished the first row.Move on to R3, since it sits in quite an odd position:

Now you are experienced enough to learn a faster way to solder the components on the bottom row. First add a small blob of solder for one pad of each component:

Now you can solder all components of the bottom row to the prepared pads:

Now you can easily fix the other pins of the components. If you have done this relax. Most of the work have been done. Just the switch, the battery holder and the ISP port is left.

3. Soldering the switch

The switch snuggly fits into the two holes on the board:

If you turn the board around you will see that the pins fit nicely on the pads:

Now you can easily solder the switch into place:

For some extra strength it is a good idea to solder the front side pins of the switch into the holes. Be careful. You need a lot of heat on the metal part of the switch and be careful to not touch the plastic lever of the switch with the hot soldering iron. You will know that you have done everything right if the solder is sucked to the bottom of the board, where it will from some nice solder blobs. So it is a messy task, but quite easy:

Now you should have finished all parts on the top of the board:

4. Soldering the battery holder

The most important thing of the battery holder is to add a blob of solder to the middle pad. Else your battery will never have good contact. So do not forget this:

The second step is to solder the metal battery holder into place. This is a task, requiring a lot of heat and patience. It is important that the whole surface of the wings of the battery holder are completely covered with solder. You will need quite an amount of solder. Be careful to not move the battery holder while it cools down. This part requires a lot of heat and that is stored in the metal part – so it takes quite a while until the solder gets solid again. In the end it should look like this:

5. Soldering the ISP header

Soldering the ISP headers is quite easy and should be no problem for you. Remember that they go on the bottom side (the very first version has no silk screens for this):

As you can see I had to get creative since all the sockets went into the kits and I had only spare parts left. No problem, even this works. If your kit has some missing silkscreen, keep in mind that pin 1 of the ISP programmer is on the bottom, inner side of the PCB, bottom left in this image.

6. Test the board

The board can be tested in two ways:

  1. Either you install the remaining machined sockets in the PCB holes of the display and solder them in place (Take care of the orientation – you want to have the display (and socekts) on the front side, where the CPU is). By that you can remove the display later for repairs. The sockets can late be easily removed if you break the plastic part of the sockets with a wire cutter and remove them with a desoldering pump, while reheating the solder.
  2. You can press the display to the sockets. This works best if you inster the display and leave a big space between the display and the PCB so that the pins of the display are just barely in the holes in the PCB. You can now shift the display vertically against the PCB so that all pins have contact to the rim of the PCB holes – it takes a bit of practice but it is sufficient to test all connections – hence a bit more fiddly.
  3. 7. Soldering the display

    Soldering the display is the last part of the Blinken Buttons for beginners kit. The display has some text on the bottom and a notch, which aligns with the white marking on the PCB:

    Now insert the display pins into the  holes on the board and add a tiny bit of solder to one pin on the bottom and the top of the display:

    Now you need to cut all display pins directly above the surface of the PCB, with a bit of the wire sticking out. It hast to be reall close to the surface, since the battery must slide over it, while you insert the battery. In the end it should look like this:

    After you have soldered the pins you should have some really nice solder bumps, like this:

    8. Finishing the Blinken Button for Beginners

    The last soldering step is to solder the safety pin to the battery holder like this:

    Again this solder joint takes an enormous amount of heat and patience. Be sure to hold the safety pin in place with a third hand – even while it cools down, which takes a considerable amount of time. Use a good amount of solder and time, to ensure that the whole safety pin sinks into the solder, to give a good physical connection.

    Now you can go back to your computer, comment the define ind ‘main.c’, line 38 and upload the firmware to you Blinken Button and enjoy it:

    Getting & moddifying the source code for the Blinken Button

    Be sure to check out the source code, because it is quite easy to add custom text and animations to your new Blinken Button!

    make

    You should check the make file. Most probably you have to adapt the settings for the programmer and its port to your environment. Upload the code with

    make install

    to you board. For consecutive uploads you can also circumvent the setting of the fuse bits by just calling

    make flash

    or you can allways set the fuse bits with

    make fuse

    Have Fun!

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