Finally, it's time to give our device a final look. Freely located on the surface of the desktop in the form of a test stand our details and modules will be placed in the box of a suitable size.
By the way, he himself. See how wonderful!
Once I made a pocket flashlight in the same case.
And now we will put a scaled pocket radio in it.
Оригинал на русском опубликован здесь.
I took it, yes, of course, again on tixer.ru, right here. Although I admit that a similar box, and even much cheaper, you can find at Ali. I did not look, if interested, you can try to search for it yourself.
Why is this box wonderful?
First of all - for its size.
The external dimensions of the case are 70x40x23 mm.
They turned out to be chosen in such a way that most of the modules of our device (almost all!) fit in well.
Of course, it is not as flat as your iPhone, but it fits comfortably in a jacket or jacket pocket.
Secondly, our box has a very simple design. No screws, bolts, washers, racks for mounting is not necessary. The back cover is closed with plastic latches, it opens easily and simply, without screwdrivers, just with a fingernail.
The transparent rectangular plate in the previous photo is cut from a plastic cap from sour cream or yogurt and will subsequently be used as an insulator.
Thirdly, this box is magical and mysterious, the truth is true.
The magic is that all the modules are perfectly placed in it, but separately, and the riddle is how to put them all together, and so that they do not interfere with each other.
Or maybe just I did not play enough time in Sokoban and in volumetric Tetris as a child ...
But enough of lengthy reasoning, it's time to start assembling!
The process is iterative, we arm ourselves with a ruler, we use a caliper and we try on each of the modules to the case and to other components, trying to figure out their mutual arrangement. If at us it turns out, we mark the holes for the controls in the case, if not, we rearrange the components separately and together in the volume of the case (just like in Tetris) and we try again.
Thus, the modules, one after the other, find their position in the housing.
As a result of several measurements, we mark up future holes.
Then we arm ourselves with a drilling machine, drill bits of different diameters and small files, make holes, from time to time we make measurements again. By the way, if there is no drilling machine, you can use a drill on the little engine, or just a steel reamer, the plastic of the case is very soft, like oil, it is easily processed.
Also, when marking and drilling holes for the loudspeaker, you can use a round metal grate to drain water in the bathroom or in the kitchen sink with a suitable hole pattern as a template.
The box after drilling looks like this.
Method of mounting a telescopic antenna:
- we place the first (thickest) link of the antenna in a couple of layers of heat shrinkage (diameter 5-6 mm), so that after heating them, the resulting diameter is slightly larger than the diameter of the hole in the housing. Thus, the layers of heat shrinkage will prevent the antenna web from falling out of the housing.
- we cut the edge of the heat shrinkage on the antenna so that the antenna placed in the case rests against the walls of the case with the edge of the heat shrinkage and the opposite side, the antenna itself must enter the case with some force.
- during the final assembly of the receiver, the side of the heat shrinkage is coated with instant glue, the antenna is inserted into the case and pressed with the glued side to the wall of the case. As the glue hardens - fixing the antenna in the case is provided.
- if you need to disassemble the structure, for example for repair, the heat shrinkage is simply cut longitudinally with a blade or a thin knife, the antenna is pulled out of it, the remains of the heat shrinkage are torn off from the housing wall. When reinstalling use fresh heat shrink.
In the course of fitting the modules to the case, we also adjust the length of the mounting connecting wires, trying not to leave too much.
In the box, the modules themselves are placed in layers, on two levels.
Since, due to the limited size of the communication between the levels in the box itself, it is difficult (I realized this only at the assembly stage), I had to use an additional connector. And at first I used a connector with a standard pitch of 2.54 mm between the contacts. As a result, the telescopic antenna was not located. I had to use a connector with a pitch of 2.0 mm.
The first layer looks like this.
The MUTE mode switch (it is partially visible under the LED of the MP3 player and above the card connector) is soldered on both sides to the MP3-player's board using tinned copper wire with a diameter of 1 mm.
The first layer in the case is placed as follows.
Between the first and second layer, you need to lay a transparent plastic insulating pad (cut out of yogurt packaging, was in the photo at the beginning).
The second layer is the radio receiver board itself with control buttons. To her to solder the second part of the connector.
In order for the receiver control buttons to be located at the desired height in the case, the button connector X2 on the receiver board had to be raised by 3.5-4 mm. It was done this way: a 1.5 mm thick polystyrene pad was glued onto the button connector X2 on the board, and another connector was glued on top of it, the contacts of which were soldered to the bottom contacts.
In the original dimensions, the board of the radio did not fit into the case, I was mistaken when designing it by 2 mm, I did not take into account that the button stroke is only a millimeter. So I had to pick up the file again and cut off part of the receiver board and part of the control button board.
In the image below, the cut off areas are bounded by a red dotted line.
After that, instead of the cut printed conductors, two wire jumpers were added. In the lower figure, the wire jumpers are highlighted in green.
It took about half an hour to work with the file, and this is faster than rebuilding and soldering a printed circuit board.
I do not plan to do the next version of the radio receiver yet, but if it ever happens, I will begin with the development of a new printed circuit board. In this case, the elements R1, C2, C3, C4 will be chosen in the SMD version - some space on the board will be freed up. Switches I also try to pick a smaller size.
I will move the radio control buttons from the separate board to the main board, select them in the corner version. This eliminates the need for connector X2. In the vacated space, it will be possible to install an inter-level communication connector (it is now hanging in the air) with a pitch of 2.0 mm.
Ceramic transition SMD-capacitors, which are now soldered to the pins of the headphones jack, can also be placed on the main board. Also on the main board we can place the headphone jack itself.
At the same time, we can try to simplify the device, perhaps by giving up the additional fee of the player control buttons to control the player using the same buttons as the radio.
I hope after such changes the file is not needed during the assembly.
Although all this may be not realized, people says, if you want to make the gods laugh, tell them about your plans.
A radio receiver with the second layer looks like this.
At some time I paid attention to the charger, more precisely to the battery charge current. It is regulated depending on the resistance of the current-limiting resistor in accordance with this table.
(Photo source: https://alitrack.ru/review/8416.html).
The initial charge current is set to 1 Ampere (resistor size 1.2 kΩ). I set the resistor to 2.7 kΩ, lowering the charge current by about two times.
The lower the battery charge current, the longer it will work.
Although to the full level with each charge will be charged more in time.
Sometime somewhere, I read that for lithium batteries, it is considered optimal to set the charge current in 1C - that is, no more than one value of battery power capacity. The power consumption of a BL-5C battery is stated at 1000 mAh (actually less), respectively, the maximum charging current is no more than one Ampere. I do not know how true this is, but I try to adhere to this rule.
The battery itself, we will try to place on the back of the case.
To begin with, we will drill a hole in the case back for monitoring the indicators on the charger board.
Then we glue a transparent plastic round top into this hole, previously cut off from the burnt-out high-power lighting LED. Yes, yes, but why else save burnt-out powerful lighting LEDs? Only for such cases. The yellow phosphor from it, similar to jelly, cannot be used, but a transparent plastic flask is very useful.
We got to the battery.
In almost every post, I draw the attention of dear readers to the fact that modern lithium-ion batteries are strongly discouraged from opening, soldering, heating, deforming, disassembling into components, flooding them with water or other liquids, shorting their contacts, and strike them with a hammer or use them bloated.
In general, batteries should be handled with care and caution.
And what do we see in the next photo? Rude violation of my own recommendations!
I soldered it.
Well, I did not have suitable springs for the contact group!
In justification, I can say that for each contact the process took place in two quick touches of the soldering iron tip. The heating temperature was controlled. The fingers holding the battery were not hot, and not even very warm, just warm. The battery cooled for half a minute.
I repeat once again - this is not good to do! So do not need to! This is a risk!
Moreover, the subsequent replacement will again have to be soldered.
But if suddenly it had to be done, it is better that the battery was at the same time pre-discharged through powerful resistors with a current of no more than 1 Ampere.
From the advantages - with the help of a soldered connector, we eliminate the situation of contact failure (or contact bounce) in the contact group during operation. But this, as we shall see, can be achieved in not such dangerous ways.
We glue a polystyrene plate with the back side of the case cover, using instant glue.
And this is what our entire power plant looks like.
Through the connector and the red and black wire the battery is connected to the charger and the power supply of the radio.
Placing the battery in such a way is quite convenient, the battery seems to be created to fit the size of the back cover of this case. But so well only in two dimensions - in length and width. And in our three-dimensional world, an extra pair of millimeters in height, unfortunately, can become decisive. What unfortunately happened.
The BL-5C battery originally planned for powering the design did not allow the lid to be closed during final assembly.
(I have already tried everything, it did not work).
But there are no hopeless situations.
And here is the solution to the problem.
This is Plan B, a fallback.
I had to, following the world's leading high-tech corporations, switch from a case lithium-ion battery to a non-replaceable Li-Po without a case. Which is a couple of millimeters thinner and has an energy capacity of a couple of hundred mAh less. And for our device, it is quite suitable.
Also, the manufacturer has already pulled a pair of wires out of it, it is very easy to solder the pin connector to them. And most importantly - it is not dangerous! Just do not make a short circuit when soldering.
The battery will be attached with using a transparent plastic plate, it can also be cut out of the lid of a sour cream jar or yogurt. Then plastic plate needs to be bent on the top and bottom side faces.
With its "ears" this transparent compartment is glued with superglue to the back cover of the case, the main thing is not to touch with glue the battery itself, its wires and the round transparent display window.
As a result, our power plant will become so.
The current consumption of the radio in a loud-speaking mode with an average volume level is 50-80 mA.
At the maximum volume level, in peak, it reaches 150 mA.
When using headphones, the maximum current consumption is 28 mA.
Quiescent current is 23 mA.
The current consumption of the MP3-player in a loud-speaking mode with an average volume level is 80-100 mA.
At the maximum volume level, in peak, it reaches 200 mA.
When using headphones, the maximum current consumption is 28 mA.
Quiescent current is 23 mA.
The output power of the amplifier with about 200-300 mW - enough for the sound in a small room.
With a battery capacity of 800 mA/hour, depending on the selected mode, a single charge of battery lasts from several hours to about a couple of days of continuous operation.
In general, this is enough for me.
To charge, as usual, we use any available five-volt power source with mini USB output.
I use a desktop computer for this, but you can use a USB charger, PowerBank or some other USB gadget.
The time until the batteries are fully charged is approximately one and a half to two hours (remember about the charging current reduced by half?).
What about the unused BL-5C? For now, just set it aside. He is still useful to us. Later. In another story.
Before final assembly, we check once again how the lid closes, everything is in order, is there anything else needed?
What about the visible indication of the charging process?
Initially, I assumed that the SMD LEDs of the charging board would be visible through the transparent window in the back cover.
But their bright light is lost in the weaves of wires.
We'll have to deliver it to the window separately and forcibly.
For example, using an optical fiber, carved from a piece of transparent plexiglass.
Or, more simply, by replacing the SMD LEDs with ordinary, on long and thin legs.
It would be possible to use one three-output two-color LED, but those I managed to find are made according to the scheme with a common cathode. And for the charging circuit, we need a connection to the common anode.
So let's make our indicator out of two ordinary three-millimeter transparent LEDs of circular cross section (I took them in a set, but you can choose them separately).
One of them is ruby red, the second is emerald green.
We trim their cases with a file, without affecting the light-emitting structure. The surface to be machined is chosen so that when the planes are folded together, the terminals of the anode and cathode of one LED turn out to be close to those of the same name.
Attach the halves to each other, having previously applied a tiny drop of instant glue on the plane of the halves from below, near the conclusions. It is not necessary to apply glue completely on the plane - the plexiglas from the glue becomes cloudy, and we need transparent lenses, at least from above.
Additionally, you can connect the halves, if you put on a strip of heat shrinkage.
Now we need to solder the anodes of the LEDs together.
We form the conclusions and solder the hand-crafted LED to the charger board, instead of the typical SMD LEDs.
Now the display is in order, visible from afar. And believe me, in fact, it is much more beautiful and cozier than it turned out in this photo.
Now we can assemble the scaled radio receiver finally.
To do this, we will disassemble it again and fold it again, this time fixing the individual modules in the case with the help of small polystyrene strips and instant glue. At the same time, we do not use any screws or nuts, since they do not fit in the housing.
I don’t show this process, because it’s difficult to disassemble something among the jumble of boards and colored wires, and it’s not very attractive. In the event of a possible repair, the glued strips will be torn off from the walls of the housing or cut off with a knife, then they will be glued again during subsequent assembly.
After assembling, I carefully shook the device over my ear, according to the results I report that it does not ring anywhere, does not creak, does not click and does not hang out. The buttons are pressed properly, the switches are switched. And yes, the main thing - it sounds! Radio broadcasts are accepted, the music library is being danced.
Visual comparison with the first version of the radio receiver.
Brief memo on device management.
Also, a few months earlier, another version of a similar loud-speaking pocket radio was assembled. Its scheme is the same, the PCB pattern is slightly different. You can see it in the title photo and below. It differs from the one described in this article by a more spacious box - there is enough free space in it, it was not necessary to be compressed.
Here, instead of one loudspeaker, a pair is applied, connected in parallel - the volume has become slightly higher.
Chrome grilles of fans, screwed on the front side of the case - a purely decorative solution. But with them, the receiver sounds, even if it is put on the table face down.
A pair of BL-5C batteries connected in parallel are placed on the surface of the back cover in the case — the receiver’s operation time without charging is twice as long.
And one more thing - it uses a slightly different scheme for an MP3 player (I took it at tixer.ru, but it’s expensive there, you better look for this module on Ali at five times cheaper).
This MP3 player board (with similar player and amplifier chips) already contains mode switching buttons, there is also an additional connector for connecting USB flash drives, and not just memory cards. Headphone jack is also present, and the most interesting is that the loudspeaker is automatically turned off when stereo phones are connected - no additional MUTE switch is needed.
That's all about the family of scaled radio receivers.
And if you have read this series of articles to the end - thank you for your interest.
And which device for repetition you will choose (and whether you need it at all) - this is up to you.
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For the publication of this post because of the low bandwidth had to wait more than a week. @cleverbot, @automation, @banjo - And I am glad to meet you again.
Sincerely, Your @mp42b.