This is a topic to guide you through the assembly of one of my DIY chest display kits. You can find them in my sales topic
here.
I took the Velleman DIY kits as an example when designing these kits and the instruction. They are perfect for beginners and don't require any knowledge of electronics to build. You just need to solder them yourself.
Depending on LED color you need to follow a different version.
For red, green and blue go
here.
For white and yellow go
hereYou will need a soldering iron, solder and diagonal pliers to cut the pins.
Follow the instructions step by step to be sure to avoid mistakes.
The components go on the side of the board with their printed icon. Soldering is done one the opposite side.
Instructions for red, green and blue LEDsThis is how your kit will come if you decided for the powerbank option:

This is how your kit will come if you decided for the 9V battery option (no USB cable and PB resistor, but with 9V clip):

Assembly is almost the same, differences for the 9V battery option will be pointed out and marked
green.
Step 1: place the resistorsPlace all the resistors in their spot and solder them. Resistors are labled with "R" and a number on the board. Resistors don't have a polarity so it doesn't matter how they are oriented. Cut the exceeding solder tails.
Place the resistors according to this list [position: value (color code)]:
R1-R5: 1kOhm (brown-black-black-brown-brown or brown-black-red-gold)
R6-R10: 47 Ohm (yellow-purple-black-gold)
(R11 is a potentiometer, this is added later)
R12: 27 Ohm (red-purple-black-gold)
R_PB: 100 Ohm (brown-black-brown-gold); this is a resistor to keep your powerbank active. (Only included with powerbank option)
This is how it looks like if you have the powerbank option:
This is how it looks like with the 9V option:
(In the following steps the powerbank resistor is not shown anymore. Make sure to add it now.)
Step 2: place the potentiometerPlace the potentiometer (small blue box) to the field labled R11 and solder it in place. Cut the exceeding solder tails.
Afterwards it will look like this:
Step 3: place the transistorsThe transistors have 3 different pins (base, collector, emitter), polarity matters! Place them as the print on the board shows: flat side to the bottom, round side to the top. The pins will be too narrow to place them correctly, you need to bend them slightly to put them in place, like this:

After soldering you can (carefully) bend the transistors to the bottom:
Step 4: place the arduinoAt first place the pin headers in their spot, longer part down. Afterwards place the arduino on top and solder it (make sure the pins are in the correct spot and the board is oriented as shown in the picture).

After that solder the pins on the other side and cut the excess.
Step 5: place the 7-Segment LEDsTurn the board, the LEDs go on the other side. Place the LEDs as pictured. Make sure the decimal points face down.

To ensure the LEDs will sit flat on the surface of the board you'll need to hold up the lower edge. I recommend to place some coins below to achieve the perfect level:

Solder the pins and cut any excess.
Step 6: place the LED barsI recommend to shorten the pins first, in my oppinion it makes placing easier. Cut them aprox. in the middle. Shown is the minimum you should leave in place.

Now you need to be sure about the polarity. Usually the bars should have a notch at one of the edges. It's quite small you have to look closely (notch on the left edge, right without):

Unfortunately this notch isn't in the same place on the different colored bars. So there is a different orientation for the colors:
red: notch to the lower left (like shown on the board)
green: notch to the lower left (like shown on the board)
blue: notch to the upper right
Now put the bars in their place and solder them, I recommend to use the coins again to assure flat placement (add one for the higher level).
Step 7: solder the 9V clip
Solder the black wire to the pad labled "GND" and the red one to the pad labled "VIN".

And you're done! Finished displays should look like this:
9V Powerbank

If you now connect the powerbank or 9V battery it should work.
End of the instrucion.
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Instructions for white and yellow LEDsThis is how your kit will come if you decided for the powerbank option:

This is how your kit will come if you decided for the 9V battery option (no USB cable and PB resistor, but with 9V clip):

Assembly is almost the same, differences for the 9V battery option will be pointed out and marked
green.
Step 1: place the resistorsPlace all the resistors in their spot and solder them. Resistors are labled with "R" and a number on the board. Resistors don't have a polarity so it doesn't matter how they are oriented. Cut the exceeding solder tails.
Place the resistors according to this list [position: value (color code)]:
R1-R5: 1kOhm (brown-black-black-brown-brown or brown-black-red-gold)
R6-R10: 47 Ohm (yellow-purple-black-gold)
(R11 is a potentiometer, this is added later)
R12: 27 Ohm (red-purple-black-gold)
R_PB: 100 Ohm (brown-black-brown-gold); this is a resistor to keep your powerbank active. (Only included with powerbank option)
This is how it looks like with the 9V option:
(The R_PB resistor for the powerbank is not shown, but make sure you add it in this step!)
Step 2: place the potentiometerPlace the potentiometer (small blue box) to the field labled R11 and solder it in place. Cut the exceeding solder tails.
Afterwards it will look like this:
Step 3: place the transistorsThe transistors have 3 different pins (base, collector, emitter), polarity matters!
Unfortunately I wasn't able to get more of the transistors I used originally and the new ones have a different pin layout. That's why the print on the PCB is currently showing them the wrong way. It's very important to place them the
opposite way like shown in the following picture.

Please excuse that the following pictures show them still in the other configuration.
After soldering you can (carefully) bend the transistors to the top (they will not sit flat on the surface, don't use too much force):
Step 4: place the arduinoAt first place the pin headers in their spot, longer part down. Afterwards place the arduino on top and solder it (make sure the pins are in the correct spot and the board is oriented as shown in the picture).

After that solder the pins on the other side and cut the excess.
Step 5: place the 7-Segment LEDsI recommend to shorten the pins first. In my oppinion it makes placing easier. Cut them aprox. in the middle (shown is the minimum you should leave in place):

Turn the board, the LEDs go on the other side. Place the LEDs as pictured. Make sure the decimal points face down.

To ensure the LEDs will sit flat on the surface of the board you'll need to hold up the lower edge. I recommend to place some coins below to achieve the perfect level:

Solder the pins and cut any excess.
Step 6: place the LED barsI recommend to shorten the pins first, in my oppinion it makes placing easier. Cut them aprox. in the middle. Shown is the minimum you should leave in place.

Now you need to be sure about the polarity. Usually the bars should have a notch at one of the edges. It's quite small you have to look closely (notch on the left edge, right without):

Unfortunately this notch isn't in the same place on the different colored bars. So there is a different orientation for the colors:
white: notch to the lower left (like shown on the board)
yellow: notch to the upper right
Now put the bars in their place and solder them, I recommend to use the coins again to assure flat placement (add one for the higher level).
Step 7: solder the 9V clip
Solder the black wire to the pad labled "GND" and the red one to the pad labled "VIN".

And you're done!
Finished displays should look like this:
9V
Powerbank

If you now connect the powerbank or 9V battery it should work.
End of the instruction.