PCB mounting: quick start from scratch

    If you remember my previous post , there was a desire to figure out what and how to add to the model I liked, so that DIY forever. Many thanks to the users of UseTi , Phmphx , lomalkin and especially n4k4m1sh1 who shared interesting ideas on this topic in the comments. It is clear that for this purpose two skills are needed, one of which is the installation of a printed circuit board. So today we will solder from scratch.



    The next set was taken from the shelf of the children's store, specifically this one .

    So, we are testing the “Young Electronics Engineer Set”. Will it be possible to use it to assemble working structures from scratch without preliminary skills, as we had before with a mechanical model?

    The kit already has everything to quickly complete the assembly:

    • soldering iron, solder with a flux channel (very convenient!) and wire cutters
    • multimeter
    • two printed circuit boards with parts

    Those. there is something to solder, than to solder, and, importantly, how to check the components and the finished circuit.

    Also, the kit includes two brochures:

    1. A methodological manual that contains general information about the devices, parts and the soldering process.

    2. Instructions for the collection of two devices included in the set and the subsequent configuration of one of them.

    The brochures are good, but, if you remember, I liked the instructions for the robot, where there were no words - only the images + the assembly was painted step by step. There are no step-by-step instructions in the instructions for this set. In some ways, this is good, because if you focus on these two brochures, if you like it or not, you will first have to read and understand everything, and only then act - that is, they teach you to think systematically. But the dynamics are a little lacking, and it seems to me that children may also lack this even more than I do. Therefore, if you collect something like that, I hope this post saves you a lot of time.

    Additional tools


    What is not in the set, but will be needed or may be needed:

    1. Tweezers. We took a manicure.
    2. Battery "Krona" at 9V
    3. Phillips screwdriver - in one of the circuits there is a terminal. Tighten the wires in it with an hour cross-shaped screwdriver.
    4. The soldering device "third hand" - that's what you can do without, although it is constantly mentioned in the instructions and brochure. Of course, it would be more convenient with it, but if you just collect all the details on the board and then turn it over, then both the boards included in the set will be relatively stable and it will be convenient to solder in principle without additional devices.
    5. Magnifier
    6. Desoldering pump
    7. Glasses and a respirator
    8. Stand for a soldering iron
    9. Fan / hood

    Of the entire list, it’s very tight only with the first two points. This time the soldering iron stand was the robot from the previous post . The rest for mounting two small boards would be really superfluous.

    But it will be useful to recall that when soldering tin pairs are released, which are not too good for health. Actually, the soldering of the two circuits included in the kit took me no more than 10 minutes and I didn’t feel bad. However, a small fan that drives smoke away, or at least an open window, is standard and very good practice. In addition, after soldering, you need to wash your hands. Eyes also need to be protected - the leg of the part bitten off by the nippers can fly off, or a droplet of hot tin can fly off during soldering (although it did not fly off). Therefore wear safety glasses. Take care of yourself!

    Nutrition


    For starters, all we need is a separately purchased Krona battery. The kit has a connector for it, which, according to the instructions, must be soldered into the first circuit. My advice: do not do this, leave it that way and use it in both schemes - both for testing the first and for setting up the second.



    The devices that we assemble consume some insane amount of mA / hour.

    If we are talking about an electric circuit, then our resources and how we quickly spend them are measured in A \ h (Ampere per hour, mAh). The capacity of a typical "crown" (passport):

    625 mA · h ≈ 0,5 · h A

    first device, "Chameleon", consuming up to 200 mA · h. Therefore, our Krona this scheme is enough for:

    625mAh / 200mA = 3.125 hours.

    which means that it is recommended to use it only to verify the operation of the circuit. A good output would be a 12 volt battery and a capacity of at least 0.5 Ah.

    mAh - this is how quickly the battery dies! =)


    It would be cool to be able to solder one of these connectors onto the boards , and then include such a laboratory power supply in it . But there are no suitable holes for any of the available connectors on the board. Therefore, we cannot connect the power supply yet.

    The first pancake is lumpy or immediately troubleshooting


    There is such an anecdote: a man bought a plane and a magazine with a description of "How to make a dead loop." Following the instructions, he got on a plane, took off, began to make a dead loop - everything turns out. Turns the page, and there: "... exit the dead loop read in the next issue."



    You can talk a lot about the culture of soldering and that this is a whole art. One thing will remain unchanged: if you do something for the first time and from a book, then at first it may not work. Here is our first board, the Chameleon set, or rather, what came of it. What mistakes were made?

    1. The soldering technology is broken, as a result - unsoldered contacts, which are better to solder and solder again (without reversing the polarity!)
    2. The technology of work is violated: each part is soldered in turn. Below you will see how much more profitable in this regard to listen to the instructions and first collect all the details, and then fix them.

    Result: the parts are beautifully crooked and oblique, and out of three chains of diodes, only one finally caught fire.

    Possible solution: unsolder all parts and re-solder.

    Positive point: you can always find. In this case, we have no "parasitic jumpers" anywhere. True, removing them is quite simple in any case: just hold a soldering iron tip and separate the contacts that are soldered together.

    To solder!


    So, the first circuit did not work out for us due to a violation of the soldering technology, so we will immediately discuss this simple and actually pleasant moment.

    The brochure clearly enough showed and told how to solder, but, unfortunately, it didn’t help me much, because it says “how to”, but I would like to understand the technique itself.

    Perhaps the best recommendation that was found was in this post . I will quote it in its entirety:

    It’s all a matter of process. You need to do this:
    • The part is inserted into the board and must be fixed (you will not have a second hand to hold).
    • A soldering iron is taken in one hand, and a solder wire in the other (convenient if it is in a special dispenser, as in the picture).
    • Solder on a soldering iron is NOT NECESSARY.
    • Touch the tip of the soldering iron of the soldering place and warm it. Usually, these are 3-4 seconds. (actually 1-2 s. - approx. A.Ch.)
    • Then, without removing the soldering iron, with the second hand, touch the tip of the solder wire with the flux of the soldering place. In reality, in this place all three parts come into contact at once: the soldering element and its hole on the board, a soldering iron and solder. After a second, “pfss” occurs, the tip of the solder wire melts (and a little flux flows out of it) and the required amount goes to the place of soldering. After a second, you can remove the soldering iron with solder and blow it.

    In addition, I can recommend an illustrated comic translated by the atarity user .

    Also, from time to time a soot forms on the tip of the soldering iron and needs to be cleaned. To do this, the industry uses special cellulose sponges, necessarily moistened with water. In our case, carbon deposits can be removed simply by shaking it mechanically - for example, the blunt side of the knife.

    Step-by-step instruction


    After the first device was unjustly ruined by us, an understanding of how to build the process more efficiently appeared. I hope this step-by-step guide helps you build your own kit just as quickly.



    So, we have a handful of details and we have no idea what's what. We take a nice manicure tweezers (that was at home) and select all resistors from this pile.



    That's what they look like. If you look closely, we will see that we have 8 identical ones, 2 more identical ones and 1 “by itself”. You need to look closely at the striped markings on the case. On the board, the place for the resistor is indicated by R (resistor). The first 8 identical ones are placed in a row at the bottom, as can be seen on the board, another 2 identical at the top left and one that is "on its own" - actually mounted on its own.

    At this stage, do not miss the opportunity to play with a multimeter. The brochure details how to measure the resistance of a resistor .

    The good news: resistors have no polarity. This means that it does not matter to us which side we put them on the board. Therefore, without thinking for a long time, we attach the necessary form to the contacts, put everyone on the board, cut off the excess with wire cutters. To make soldering convenient, we placed the board on the edge of a small cardboard box, because if it was put on the table, this would not have made it possible to solder the resistors a little above the board, as recommended.



    That's what we get. Still far from ideal, but much better than the first set! We continue.



    Now select all the capacitors. On the board, places for them are indicated by C (capacitor). Capacitors are polar, and there are non-polar. This means that some capacitors, if they are put on the board by the “wrong side”, will not work and the entire circuit will not work. Hint: the yellow capacitors are non-polar, so just put them in the sockets C3 and C4.

    Cylindrical capacitors are polar. How to determine the polarity? Two ways:

    1. Before trimming the legs, the one that is longer is a plus. It is enough to combine it with the marking “+” in the mounting socket of the capacitor C1 or C2

    2. The blue bar on the capacitor is the “key”. She is where the minus is. It is enough to place it on the back of the plus marking.

    Hint:If you think laziness, just plant the polar capacitors as in the image.



    And the diodes! Diodes are all polar. Ways to determine the polarity:

    1. A longer leg is a plus.
    2. Chamfer (bevel) on the side of the base of the diode itself. Not very convenient, because transparent diodes almost not see it at all. All the chamfers of the diodes on this board should be on the one hand - the outside.
    3. Put the multimeter in dialing mode (the “wi-fi” icon, but in fact - a sound signal, on the multimeter), touch the short leg with the black wire (minus), and the long leg with red (plus). In our case, the diode will light up. If you change the polarity - will not light up. This is because the diode passes current in only one direction.

    If you reverse the polarity of at least one diode, then the entire chain will not burn. But! These three methods for determining the polarity of the diode have not failed us. The latter method can be used again after installation for ringing the circuit and to make sure that the polarity of the diodes is not violated.



    We only have a few more details left. Clockwise in the photo:

    Button. Not polar. Just put and push lightly - it will fix on the board.

    Chips:they have “keys” on top of the case. The one that is longer is a recess, which must be combined with the designation on the board. In our case, the recess will look to the right, towards the resistors. The microcircuit has a smaller key in the form of a recess in the upper left corner. There he should be on the diagram. Also, this recess is schematically indicated on the board, also on top.

    Pay attention to the good old "tube" (in the sense - cozy) DIP-chips . Now, in addition to kits for creativity, there are already few where to meet them, although soldering them for me personally is a pleasure, as well as assembling gear mechanisms. In industry, the traditional methods used by our parents and grandparents of those who are destined for this set have been replaced by surface mounting .

    Microchip voltage stabilizer . With her, everything is simple, nothing will be mixed up.

    Terminal connector Here we will connect the power supply. Therefore, it is important: at the terminal connector, the holes for the wire should look outside the board, otherwise they will be closed by a nearby capacitor, and it will become difficult to rivet the wires in the terminal (in fact, it happened with us). In case of improper placement of the terminal connector, it will most likely fail to remove it without a vacuum desoldering pump (we did not succeed).



    Done! We managed to make only one significant error during assembly - this is the location of the terminal connector. But this does not affect the polarity, but rather the ease of use.

    We got a mini-testing device that will always show how much more battery is left. Now we will set it up to check the Krona battery, which we already have and in which the charge is 9V, until it runs out.



    Remember, we recommended you not to solder wires with battery terminals into the first circuit? If soldered, solder, now we need them.

    We connect a new, not yet dead battery. We observe the polarity (the positive terminal connector is indicated on the board). The first red LED lights up. The circuit works!

    Briefly press the button once. The device measures a voltage of 9V and remembers it. If we had a nearby Crona, we could check the charge difference.

    Hint:Crona can be quickly discharged using the first scheme if you, of course, assembled it correctly. As we already said, it consumes up to 200 mA, so it will drain the battery in about three hours.

    Actually, the multimeter included in the set also copes with the same voltage measurement functions , but it does it, of course, not so spectacularly. If you have a laboratory power supply, you can reprogram our device every time under a new voltage. The same thing can be done by connecting different batteries and again pressing the “remember” button.
    In conclusion, I want to say thanks to those who invented and created this kit . Two days ago, I had no idea about the process of mounting printed circuit boards. Now I distinguish the resistor from the transistor and I can put them on the board using keys, a multimeter and other tips. In addition, one of the devices I was able to immediately assemble and put into operation! As always, it is very nice: to see and hold in your hands what you managed to collect yourself.


    Thanks to this two-day immersion in electronics, it became clear to me that I also want to find out:

    1. How to ring the mounted printed circuit board to find where the defect is and fix it, rather than solder the entire board (I still have hope to rebuild the first device !).
    2. How to calculate the power consumption of the circuit and independently calculate how long this or that battery charge lasts?
    3. Three indicators that we measured during the assembly process using a multimeter - the number of volts in the battery, the resistance in ohms of the resistor, and the measurement of current in amperes. How are they interconnected and what can I do about it?
    4. How to read the circuit diagram of the device and see it on the board? How to combine paragraph 3 and paragraph 4?

    Therefore, I want to contact you, Habr. Please share links to articles and books on this topic that you liked, that are easy to read, and quickly understand.

    And also, tell me, please, what would you do with powering the devices, terminals and connectors, because so far I only have the option of “two protruding wires and a Kron battery”.

    I hope this review also helps someone to "enter" the desired topic faster and easier. Good luck to you!

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