read a bom and fill your pcb

In this article I will tell you how to read a Bill Of Materials (BOM), identify your kits components and how to correctly place them on your Printed Circuit Board (PCB).

Before going any further, we’re going to get some reminders on
PCBs, BOM, and every piece of equipment you need to work well. If you’re already familiar with this stuff, you can skip the explanation and go to the tutorial part by clicking here.

what you need on your bench

recommended tools

Here’s a list of tools you’re gonna need. You don’t have to get all of these tools in particular but it would help a lot.

my favourites

• A multimeter, it’s a very useful measurement equipment for any electronic advice. Resistor, voltage, current, capacity… And the prices go within a very large range. The good news is that you can find some pretty decent ones. So here’s our little selection : This one is on sale for 14$ and this one for 30$. It’s up to you considering how often you will use it. Just know that you can deal the tutorial without any mulitmeter if you learn the resistor color code!
• A PCB holder, I admit this is luxury but I love it! Secure your PCB bewteen the 2 clamps and putting the components becomes much easier. You can also make it without this equipment by working directly on the table but it’s less convenient.
• A storage cabinet for your components. It allows you to sort them by values. The point is to deal directly with our suppliers and to order 100 pieces of each resistors, and never have to sort them again ! If you’re to realize pedals quiet often, this way is much more economic and time saving.

classics

• A round nose plier, it’s a very useful tool we use on a daily basis. It allows you to properly fold components legs and to get a good grip on cables once they’re deep into the housing. It’s a plier, you can hold approximately everything with it. At this time of the building, it is not essential, but you will need it in the following tutorials. So don’t waste time!
• A 3rd hand holder will facilitate the wiring of the switchs and pots in the next tutorial. You can use it not only for wiring but also to hold your card while mounting the components.

documents and equipment you need before you start

1. To read the BOM, you need… the BOM in front of you!
2. The electronic schematic of your kit (if you wish not only to assemble it, but also to learn more about it)
3. The DIY kit with the components and the PCB.

technical information

This is a reminder on some interesting notions. You can skip it and move directly to the assembling.

the pcb (printed circuit board)

If the pedal is the body, the PCB is the heart! It contains all the connections to give life to the schematic

how do we make a pcb

Most of PCBs are made in Asia, you just have to be specific to get what you want. For your own prototypes, I’d advice you to go to PCB Way. It is more than enough if you build PCBs from time to time.

Our PCBs are made from a FR4 plate (some sort of plastic fiber). On each side, the manufacturer adds a copper layer. Then only our routings, that we make with a software, are kept in the copper layer. Afterwards a milling machine drills the plate, and a surface treatment metallizes the holes. The plate is then coated with a thin gold layer that protects the whole card from corrosion. Finally, instructions are drawn in a white writing to indicate component placements, board serial number, etc…

how to make your own pcb

You may have guessed, to make a PCB, you absolutely need a good technical drawing. That’s what we call a typon, and we get it using a CAD software.
Our team works with Eagle PCB, the interface is user-friendly and there are a lot of available librairies.
Then, when we discover new sounds in the R&D department; we go onto this sofwtare, draw the schematic, and make the routing.

Indeed, The schematic is a visual and very simple to understand form. Anyone can understand it very quickly and it’s a necessary step before making the PCB. We can also transfer the schematic to another software and simulate how it works.

the bom (bill of materials)

Once we receive the PCBs, all we have to do is to export the BOM from the software. It is actually a list containing all the components that must be on the board. We know what to choose, what it is, and where to solder!

I’ll explain to you how to read it :

• The title. You ABSOLUTELY need the right BOM for the right PCB ! The serial number is written on it, check twice that everything is clear before staring.
• Column Quantity, quite obvious isn’t it. That’s how many of each components you need. So you can take all of them at once. Then you just have to place them to their location. Save some time !
• Column Value, as we sorted the components by their values, this column tells you which one you need to take.
• Column Noun. Once you hold your component, you have to check the footprint on the board to know where to mount it. See below to learn more.
• Column Package, it’s a technical information about the product line to choose. Convenient when you’re used to make DIY projects and that you want to order you components by yourself.
• Because we try to be nice with you, we cut the BOM document in several sections. First section is “RESISTORS”, then “CAPACITORS”, etc… It is clear, you can’t get lost and sections are in logical order. So you’ll see next that there are a bunch of types of components and you’ll enjoy this attention to detail. 😉

mounting of the electronic components

In this part you’re gonna discover how to mount each of the components on your board! At the same time I’ll tell you how where they come from, how to identify them and why we use them.

resistors

color code method

Whenever you have a pedal, you have resistors. They resist to the current flow in a circuit (hence their name). And if you learn a bit more about electronics, you’ll learn that you can do much more functions !

To identify a resistor value, given in Ohms (Ω), manufacturers agreed on a common color code. This color code is made thanks to color rings on the resistor, which translate into values.

For your information, we relieve mathematical writings such as :

• k = kilo = 10^3 = 1 000
• M = mega = 10^6 = 1 000 000

To give you a order of magnitude, values betwenn 1Ω and 1kΩ are considered small. Between 100kΩ et 2.2MΩ is considered super large!

multimeter method

You want to go easy ? Switch on your mulitmeter on Ohmeter mode and read their value thanks to the probes!

okay then, but why ?

When you’ll get your FX Teacher kit delivered, you’ll have a bag with different value resistors mixed. You’ll eventually need to know which one is the 10kΩ resistor to put on R4!

2 Options :

• Each time you find a resistor, measure it and mount it on your board. Not to complicated ! But it’s a another step beside. I used to do my first boards like that, but not anymore!
• Or you can use a storage cabinet to store a lot of resistors in it, from various values. By buying them by 100 it becomes much more affordable and they are already sorted. Just store each references in each drawer and this is done! This quantity might seem to be a lot at first, but you won’t have a lot left after making less than ten pedals.

how to mount them on board

why this kind of resistor and not another one?

There are dozens of different resistor types and manufacturers ! While some still like carbon resistor for their vintageness, they are not very precise and they are noisy. So we trusted the brand Xicon with their metal film resistors.
They offer a much more precise value, with a 1% error rate. And, a thermic sensibility of 50ppm which is ridiculous. We chose a line with a power handling of 1/4W, which is more than enough for pedal manufacturing.

With this line I’m sure not to alter the quality of my electronic design! This is why we trust them for the production of our Anasounds pedals for years.

capacitors

operating principle

capacitor physics

A capacitor is made of 2 metallic plates separated by an insulator. When we apply a voltage on its terminals, the 2 electrodes get positively loaded on one side, and negatively loaded on the other one. Once we release this voltage, both poles are going to discharge energy in the circuit. Considering their value, this amount will be released quicker or slower.
A current is generated in the circuit depending on the formula i(t) = C * d u(t)/dt.

i is the current injected in the circuit. C is the capacity of the capacitor. u is the voltage on the capacitor terminals.

the types of capacitors

The first domain of improvement focused on by scientists was the insulator. We don’t use any capacitor for any situation! So we selected 3 technologies for differents uses, ceramic, film et electrolytic.

Some capacitors are polarized which means that they have to be mounted respecting a + and a -. And others are not, meaning that how you place them doesn’t matter.

One last thing to remember about capacitors, all of them have a specific charge voltage ! It means that we furnish you capacitors with a charge capacity of 25V and 50V depending on their types. It is more than enough pedalwise. But be careful, don’t try to mount one of this caps on the power supply stage of an amp. It will litteraly blow to your face! It’s déjà vu…
Also something loved by “vintage” manufacturing, caps with 250V charge voltage for a guitar signal… It will be the opposite, using voltages between 20mV and 18V. Good luck exploiting it to its full potential . The cap will just age faster.

our capacitors lines

Type	Ceramic	Film	Electrolytic
supplier	AVX, USA	Kemet, USA	Nichicon Japan
line, type	Z5U	Polyester, R82	UFW
value ranges	1pF – 470pF	1nF – 1uF	1uF – 470uF
pros	Filter high frequencies. Low serial resistance.	Filter a wide range of frequencies with high audio quality (low distortion). Very low resistance value.	Filter very low frequencies like 60-cycle, stock and release current in power supply circuits.
cons	Piezoelectric sensibility	More expensive than ceramic and even more if miniaturized	Limited life expectancy, so we better choose high squality once !
polarized	No	No	Yes

p = pico = 10^(-12) = 0.000 000 000 001
n = nano = 10^(-9) = 0.000 000 001
µ = micro = 10^(-6) = 0.000 001
m = milli = 10^(-3) = 0.001

F = Farads, unit used to represent the capacity C of a capacitor

ceramic

Ceramic Capacitor are not polarized ! So we can mount the way we want . Leur valeur est toujours en pF.

For values, there are 3 numbers on the capacitor. First 2 indicate its value. Third one indicate its power of ten.
Here are a few examples :

• 471, is 47 x 10^1 = 47 x 10 = 470pF.
• 101, is 10 x 10^1 = 10 x 10 = 100pF.
• 470, is 47 x 10^0 = 47 x 1 = 47pF.
• Etc…

Once you know its value, you just have to mount the capacitor.
As usual,read the BOM, identify the value and find the name on the PCB. Then place it and fold the legs outwards.
Now you just have to solder!

film

read film capacitor value

Film capacitor are not polarized either! You can connect it either way.
The value indicated on it is whether given in µF or nF.
Thus, we mark it all as nF on the BOM except for 1µF. It avoids writting 1000nF, which is mathematical heresy!
I might suck out some of your brain cells witht his part.
Once you know how to read one, you can chill for the rest of your life!

• .1, means 0.1µF = 0.1 x 1000 n = 100nF
• 1u, means 1µF so nothing changes
• .47 is 0.47µF = 0.47 x 1000n = 470nF
• 47n is 47nF, There’s no trap!
• 10n is also 10nF, fiouh!
• Etc…

mount a fil cap on the PCB

How to do it, as said it is not polarized so there is no reverse. Then push it in and fold the legs outwards. What remains is soldering!

We use this wonderful line of capacitor because they do not produce any harmonic distortion! It is unfortunately quite differetnt from ceramic capacitor . That’s why we would rather use film capacitor for filtering.
When we go above µF we have to switch to electrolytic caps. This is the challenge of our R&D team to stay between 1nF and 1µF on filtering.

electrolytic

read electrolytic capacitor value

So they are the only polarized capacitor we used!
Once we have read its value, we have to discover where are + and –
terminals to place them!

To read its value, this is super easy! They are pretty big, so everything you need to know about them is written on ! Moreover, All electrolityc capacitor have values in µF So no doubt allowed about it.
if you read 47 or 47µF, it’s 47µF !
However be careful not to confuse the capacitor value with its operating voltage! Most of the time 25V, 50V and 100V.

mount electrolytic capacitor

To find the “-” terminal, there are 2 approaches:

• If the component is new or not yet pre-cutted, just check the shorter the leg!
• Check on the side of the component, there are “-” symbols drawn on!

On the PCB, we always indicate the “+” terminal, inside or outside the cercle. Just know that the “-” is on the other side. It’s in the bag!

We chose Nichicon because one of their line is dedicated to audio applications! Very low ESR (equivalent serial resistance) , so definitely something we don’t want!
Finally, It has a life expectancy of at least 2000 hours at least in load.
These characteristics are over average and the price/u stays coherent for effect pedals

the semiconductors

theory and evolution

Semiconductors are part of the active components family!
Resistors and capacitors are passive components awaiting for a signal and energy to interact with the sound.
Active components are power supplied and can by themselves generate a signal or amplificate it.

In the first half of the XXe century, the diodes apperared. Then after WW2, silicum and germanium diodes come to the market! By assembling 2 PN
junctions (diodes), we discovered the transistor in 1947. It was a true revolution, because the transistor can amplify a signal the same way lamps do ! (they apparead in 1919). The first transistor radios were born in 1954. Then come in 1958 the printed circuit boards with the first op-amps! It’s a set of miniature transistors integrated in a chipset that can achieve a lot of functions and operations!

This innovation led to the creation of microcontrollers, microprocessors that are composed of even more transistors, billions, always smaller and more efficient…
This is the domain I grew up in. When I worked at NXP Semiconducteurs, we were developping integrated circuits in the audio technologies.

diodes

recognize them

To know a diode value, you must read each letter around its surface. This value starts in 80% of cases by “1N”. Only a few diodes like the 1N34A don’t have their name written on it. Thus, we have to identify them with practice…

place a diode on the pcb

Once we have the value, we have to be carefgul, there is direction on the diode and it is very important! the ring drawn on the diode shows the cathode, the “-“, it is also drawn on the PCB. Then you have to mount it with the stripes of diode and of the PCB on the same side.

In pedals, we find diodes for various fucntions :

• Clipping! Diodes clip the signal which creates that distortion we love so much. See the article.
• Power supply protection, current can only go through the diode in one direction, from the anode to the cathode. Thus, the current enters through the side without the ring to the side with it. By cleverly using diodes, we can block reversed power supply connection from destroying the device. We just have to take care that the diode doesn’t burn due to a too intense voltage. So PLEASE when it’s written”9V DC” on the pedal, don’t plug a 18V power supply if the manufacturer doesn’t allow it. Or there will be smoke!

transistors

identify transistors

To begin with, there’s a lot more room on a transistor to write things!
On the flat face is written the value (Most of time starts with 2N or BC). The round face is used a mark. This curves are also drawn on the PCB to identify where to put which side.

Transitors are made of 3 electrodes. Regarding the transistor itself, they have different functions and different connections. (If you want to learn more, search “YOUR TRANSISTOR REF” then “PINOUT”). But in our case, there is no need to do it!

mount a transistor on a pcb

Plug the transistor, fold the legs and solder, once more, that’s all you have to do!
In our circuits, most of the time we use transistors to amplify a signal or to adapt impedances. Look the buffer from this article. And we’ll talk about it later in future articles.

intergrated circuits (op-amps and others)

We can read its value directly on the top of the IC. NE555, TL072 etc… Remember to solder the socket first, then plug the chipset on it.

Warning, IC need to be placed with a specific direction! Each leg is very important and does rigorously different thing! So make sure to mount the socket first. Whether a stripe or a dot for the ICs, and a notch for the socket and the PCB.

Op-amps are very nice amplifierswith which we can do a lot of things! High quality filters, give gain to the saturation stage, etc…
It’s a primordial component to all of our designs! We’ll talk about it more in depth later too.

trimpots

identify the trimpots

Trimpots are nothing more that miniature potentiometer on PCB ! They allow us to offer thin adjustments and to add settings.

On the pic, the left trimpot is shown in top view. There is a screwdriver print with 2 half-circles. It shows us the cursor of the trimpot. Here it is halfway of its total range.

The right one shows the value indication. It’s quite like ceramic capacitors, P103 for 103. 103 being 10 x 10^3 or 10kOhms.
Yes trimpots unit is “Ohms” just like resistors, simply because they are variable resistors!

mount a trimpot on a pcb

Once placed, as usual, fold the legs outwards,flip, and solder !

Common values :

103 = 10kOhms
203 = 20kOhms
503 = 50k Ohms
104 = 100kOhms
105 = 1MOhms

terminal block

We’re going to see them a lot with FX teacher ! On one hand it is soldered on the PCB thanks to its legs. On the other, we connect the new component we want thanks to the hubs. To do so just screw it to connect it to the circuit!

It’s great tool for learning and audio discovery that we cherish at Anasounds!

Of course, be careful to place it in the right direction. So you can easily access the hubs to put component legs.
We left some free room around them to manipulate and let the components breath.

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