100% Handmade Electronics for Beginners



    The article describes some of the stages of manual manufacturing of electronic devices, and especially in detail about the first stage: the manufacture of a printed circuit board. Detailed photos of the process will help to understand the details. And for dessert, to consolidate the theoretical material, we will assemble the simplest electronic piano on the NE555 integrated timer.

    Prologue

    We are all consumers of electronic devices: telephones, tablets, televisions, etc. But only one out of a thousand can roughly imagine how it all works "from the inside out", and only the elite are truly capable of creating an electronic structure from scratch with their own hands. We invite you to join the club of the elite. Read this material, and if it interests you, try your hand at mastering man-made electronics!

    Those of you who find the strength to read the article to the end can proudly declare themselves “I understand something in the production of electronics”, and even those who accomplish the feat and master the assembly of the proposed design are quite worthy of being awarded the title “Real Electronics Engineer” Profi ”(well, almost).

    This master class is based on the Master Kit NN201 kit , which includes parts and materials necessary for the manufacture of a printed circuit board and electronic piano. Of course, if you wish, all materials and tools can be purchased independently, you only have to spend time searching and buying the necessary components.

    The necessary theoretical minimum

    Any electronic design contains dozens, or even hundreds and thousands of components: resistors, capacitors, diodes, microcircuits, etc. All these components must in a certain way be electrically and mechanically interconnected.

    The simplest circuits can be soldered “on the knee” by wall mounting, but this design is ugly, confused, and has dubious mechanical rigidity. Therefore, in any serious electronic design there should be something like a chassis on which all the details are mounted. In different years, the chassis was also made of metal, cardboard or plywood, but in the last 20-30 years, the printed circuit board has been the technological standard of the chassis.

    A printed circuit board is a sheet of dielectric material on the surface of which, in a specific configuration, strips of conductive material (usually foil) are applied. Glass base is most often used as a base: it is non-combustible, has high dielectric properties, and is inexpensive. In fiberglass, holes are drilled into which the conclusions of the parts are passed. On the reverse side of the board, the terminals are soldered to the copper conductors, which are configured in a certain way. Thanks to the soldering, the components are mechanically fixed to the board, and thanks to the copper conductive paths, the leads of the parts are electrically connected to each other.

    Of course, copper conductors can be glued to the fiberglass board in necessary places. But it is technologically simpler to do the opposite: take a sheet of PCB with an already glued continuous layer of foil and remove the foil from unnecessary places.

    You can remove the foil from unnecessary sections mechanically: by making a slot with a sharp knife in the necessary sections. However, this method is time-consuming, traumatic, and is primarily suitable for the most simple schemes.

    The foil can also be removed chemically: it is enough to immerse the board in a solution that corrodes copper (most often, a solution of ferric chloride is used). Only previously it is necessary to protect from the solvent those parts of copper (future current-carrying conductors) that must be preserved. As such a protective agent, varnish is sometimes used, but it is more convenient to draw tracks with a special marker. Also in the practice of electronic engineers, the so-called laser-ironing technology (LUT) has become widespread. With this method, the pattern of future current-carrying conductors is printed on a laser printer on special paper. Then the paper is applied to the fiberglass blank and ironed this “sandwich”: as a result, the toner particles remain on the blank and will not subsequently be etched with a solvent.

    The foil removal process is called pickling. Etching continues depending on the concentration and temperature of the solution from several minutes to an hour. After the end of the process, the board is washed with water and the protective compound is removed, under which copper conductors should remain.

    Then, holes are drilled for the outputs of the components. Microdrills and drills with a diameter of 0.8 ... 1 mm are usually used. Copper quickly oxidizes in air, and this complicates its soldering. Therefore, immediately before soldering, the board must at least be cleaned with a fine sandpaper, thereby removing the oxide layer. But it is best to cover the copper conductors with a protective compound - a layer of solder. This process is called tinning, and this allows you to maintain a high degree of suitability of the board for soldering for several years.

    In production conditions, a so-called solder mask is also applied over current-carrying tracks - a layer of protective material. This layer protects current paths from accidental short circuits and damage. Only contact pads remain mask free, making it easy to solder.

    Another technical process - silk-screen printing - involves applying to the “front” side of the board with special paint marks and inscriptions. This simplifies the life of circuit board installers and repair specialists.

    But at home, it is difficult to carry out the processes of applying a solder mask and silk-screen printing, so we will not do this.

    Everything, the circuit board is ready. After that, all components are mounted on the board, and then soldered. Then the resulting design is tuned and tested. In modern factories, most of these processes are performed by industrial robots, but we are people, so we will do everything with our own hands.

    The long-awaited practice.

    It is much more interesting to make not just a boring printed circuit board, but a circuit board on the basis of which you can assemble a practically useful device. We will make the simplest electric musical instrument - a toy piano with 8 keys.

    Materials and components that we will need:

    - prefabricated foil fiberglass with dimensions of at least 10x15 cm;
    - a marker (preferably lacquered) or nail polish to protect live paths (the marker can be found in stationery stores, and borrow the varnish from mom / girlfriend / wife);
    - ferric chloride - a powder weighing 100 grams is enough for the eyes;
    - drill and drill with a diameter of 0.8, 1.0 and 1.2 mm;
    - non-metallic bath (deep bowl) - our workpiece should fit in it. It is better to find some old unnecessary container, because after our experiments it will probably have to be thrown away or continued to be used for etching;
    - rubber gloves to protect our hands from mortar.

    Note that in the Master Kit NN201 setincludes a workpiece with already drilled holes, a special felt-tip pen and a beautiful red jar of ferric chloride weighing 100g. The kit comes in a plastic blister that serves as an excellent etching tray!

    For soldering, you will need:

    - a soldering iron, side cutters, solder, flux;
    - radio components, a list of which is given below.

    Everything you need can be found in radio stores or household goods.

    Layout diagram of current-carrying conductors of the printed circuit board (view from the side of the foil):


    Preparing the printed circuit board for etching

    We clean the board from the side of the copper layer with fine-grained emery paper (in extreme cases, a rough ink eraser will do) and degrease it with alcohol or gasoline;

    We apply the template to the printed circuit board and drill holes at the required points;

    We draw with a marker a drawing of conductors and soldering pads, focusing on the wiring diagram and the drilled holes, trying not to "slap" the foil with your hands too much (therefore, it is advisable to work with thread gloves). In case of errors, the marker is easily washed off with alcohol solutions. The dimensions of the contact pads for the findings of the parts can be made larger (where the space allows).

    It is convenient to apply drawings using a ruler, in two layers. After drawing the drawings, you need to let the board dry for about 10 minutes, then inspect the board and fix possible errors: draw up where the layer turned out to be thin, and scrape with the awl or thick needle the places of the erroneous merging of the tracks or pads.

    Preparation of the solution and precautions

    Now you should prepare a solution of ferric chloride. To do this, 100 grams of ferric chloride should be stirred in about 200-250 grams (one cup) of warm water. It is not necessary to measure everything accurate to a gram: the process will go on and with a slightly different ratio of ferric chloride and water, you just need to consider that the etching time of the board depends on the concentration of the solution and its temperature.

    When preparing the solution, the basic safety rules must be observed:

    • work in rubber gloves in a ventilated area !;
    • Do not lean close to the solution: harmful fumes are released !;
    • falling on objects, the solution leaves indelible rusty spots, therefore, care should be taken to prevent powder or solution from falling onto surrounding objects !;
    • prepare the solution in a glass or plastic dish, but not in metal, its solution will corrode !;
    • stir the solution with plastic (disposable spoons are very convenient) or wooden objects (an unnecessary pencil);
    • the optimal temperature of the solution is 45-50 degrees;

    Now everything is ready for the etching process of the board.

    Board Etching

    • Pour a solution of ferric chloride into the container;
    • carefully place the board with the foil up in the solution so that the solution with a margin of 5-7 mm covers the entire board;
    • the duration of the process depends on the temperature and concentration of the solution and takes from 10 to 30 minutes. To reduce the etching time, it is advisable to shake the blister so that the solution is mixed and fresh at the points of contact with the foil;
    • visually observe the etching process: first, the foil sections on the edges of the board and near the drilled holes begin to be etched due to the fact that the solution in these places contacts the foil not only on the plane, but also on the foil cut;
    • when all excess foil has settled, carefully pour the solution into a container for subsequent use or disposal;
    • place the blister with foil under a stream of warm water and thoroughly rinse (with gloves!) the blister and the board. We make sure that the rest of the solution is actively diluted with water before entering the sink, otherwise yellow spots will remain! You can first put the blister in a non-food container with water and start flushing in it;
    • you need to wash the board in a solution of any detergent or soap, for this you can use a foam sponge moistened with water and detergent;
    • finally rinse the board with warm water, then dry it with paper towels;
    • remove the protective layer applied with a felt-tip pen using an alcohol solution applied to a sponge or rag: wipe the board several times until the protective layer is completely removed;
    • thoroughly rinse the detergent board again and dry (see above). If there is any doubt whether the board got grease from your hands or from somewhere else, you should once again clean and degrease the board. After that, do not touch the foil with your hands. The board is almost ready!


    Tinning of the conductors of the board (optional, but desirable process)

    • We cover the circuit conductors with a layer of alcohol-rosin flux (SCF) or neutral flux LTI-120;
    • tinning is done with a well-heated flat-tip soldering iron;
    • immerse the tip of the soldering iron in the rosin, then take a little solder on it and apply the tip to the track;
    • hold the tip for a few seconds - so that the solder starts to drain from the tip and spreads over the heated conductor, and slowly push the tip along the conductor, while the solder should reach for the tip and cover the track. No need to rub solder into the track: it spreads along it itself if the track is sufficiently warmed up. The speed of the sting is selected empirically.
    • Do not keep the soldering iron tip on the same section of the board for more than a few seconds: otherwise the copper conductor may come off the board;
    • the holes should remain free of solder. If the solder has closed the hole, you need to clean the tip of the soldering iron, dip it in rosin and attach the tip to such a hole;
    • Similarly, you need to irradiate all the tracks on the board.


    Check if the tracks are correct. If there are still errors, they can be corrected by cutting unnecessary tracks with a sharp knife or by soldering instead of missing pieces of wire.

    Now the board is ready to install and solder the components.

    Description of the circuit operation

    Consider the circuit of our design.
    The circuit is based on the well-known NE555 chip. The microcircuit is turned on according to the classical generator circuit, the frequency of which is determined by the C1 capacitance and the resistance between the pin “2” of the microcircuit and the “+” power supply. When the buttons SW1 ... SW8 are pressed, different tuning resistances are included in the frequency-setting circuit of the microcircuit - accordingly, the BA1 speaker emits sounds of different tonality. As a result, even with such an elementary musical instrument, many simple melodies can be performed.

    Instrument tuning is done with trimming resistors VR1 ... VR8.

    Schematic diagram:



    Installation diagram (view from the side of the parts):



    We will need the following parts, which can be purchased at the radio store; All these details are part of the NN201 kit:

    1. IC1 (microcircuit) NE555P 1 pc.
    2. C1 (electrolytic capacitor) 10 μF 1 pc.
    3. C2 (ceramic capacitor) 0.1 μF 1 pc.
    4. R1, R2 (constant resistors) 10K 0.25W 2 pcs.
    5. SW1-SW8 (buttons) B3F4005 8 pcs.
    6. R3-R10 (tuning resistors) 3362P-1-103LF 8 pcs.
    7. SP1 (speaker) 0.5W 8R 1 pc.
    8. B1 (battery terminals) 1 pc.


    Board mounting and soldering

    • install all components on the board, focusing on the list and wiring diagram;
    • we pay attention to the correct orientation of the microcircuit (the key in the form of a semicircular recess in the upper part of the microcircuit should be oriented as indicated on the wiring diagram) and the electrolytic capacitor (the negative terminal is marked on its case by a gray stripe and the sign “-”; on the wiring diagram, it is indicated Conclusion "+" of the capacitor);
    • so that the parts do not fall out of the printed circuit board, we bend their conclusions from the side of live tracks;
    • we cut the conclusions of the components. Ideally, the lead should not protrude more than 2-3 mm from the axis of the hole.
    • solder all the conclusions;
    • we check the quality of soldering: the absence of unsoldered conclusions and stray short circuits, if necessary, eliminate the noticed errors.


    Switching on and tuning We

    connect to the circuit a dynamic head and a Krona battery. If the board is made correctly, and the soldering is done correctly, then when you click on each of the buttons, the speaker should reproduce sound. Now it remains to adjust the tuning tone of the VR1-VR8 resistors for each of the eight buttons, focusing on a real piano or synthesizer (you can install the appropriate program on your phone or tablet) or your own hearing.

    Setup should begin with a VR8 resistor. It matches the highest tone. Press the SW8 button and rotate the VR8 resistor with a thin screwdriver. The sound from the speaker should correspond to some note of the second octave, for example, To. The next note should be a semitone lower - the C of the first octave. Press the button SW7 and rotate the resistor SW7, the next note is lower by a tone, and so on with each button. After tuning all eight notes, you get a full octave.

    Now you can enjoy the result of work and try to play some simple tunes!

    Appendix: photo gallery of the etching process of the board

    1. The cleaned board with holes.



    2. A board with a drawing of conductors with a felt-tip pen.



    3. Board in a blister with a solution of ferric chloride immediately after immersion. The temperature of the solution is about 45 degrees.



    4. The beginning of the etching process - the edges of the board and the board around the holes are etched first (after about 5 minutes).



    5. Continuation of the process - after about 10 minutes. Do not forget to swing the blister to accelerate etching.



    6. Etching is almost finished, there are small areas with a thin layer of foil. After about 15 minutes



    7. Etching is completed. After about 20 minutes



    8. Washed circuit board until traces of felt-



    tip pen are removed 9. Traces of felt-tip pen are removed, conductors are not tinned yet.



    10. The flux is applied to the conductors, after which they are tinned.



    11. The conductors are tinned, the flux washed. The board is ready to install and solder components.



    12. View from the soldering side after installing the components.



    13. The device is assembled.


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