Construct your individual single board pc
Background
Again in April, the hardware news site cnx-software featured a really good new small Linux board known as Breadbee, that was designed and nonetheless being developed by one of many website’s readers, Daniel Palmer (aka ‘dgp’). The board has many distinctive particularities that appealed me:
- it’s small, very small, about 3x3cm, barely bigger than the Ethernet jack, as a result of sure, at this measurement, it comes with Ethernet!
- it’s fairly low-cost, roughly $10 for a whole board in small portions
- it’s totally made out of discrete parts which can be human-friendly and it may be assembled at residence!
- regardless of its small measurement, it comes with a 1 GHz Cortex A7 CPU, 64 MB RAM, 16 MB SPI NOR flash, and has loads of I/Os out there.
- Daniel needs it to be not solely blob-free, but additionally supported by a mainline Linux kernel
Daniel had began assembling and freely giving just a few of those to varied testers. I may have been however had no instant use case for it and did not wish to abuse. However Daniel insisted on sending me the required components in order that I may attempt to assemble two boards. I suppose he was interested by testing how possible it was for the board to be assembled by an novice, and in sharing expertise to enhance the design. With that in thoughts, I lastly accepted, and after just a few months (as a result of lock down right here) I obtained his bundle with all of the parts to make two boards plus fairly some extras permitting me to fail a number of occasions.
Presentation of the board
The board exists in two variations, the unique one, made by JLCPCB and the brand new one, made by OSH Park with a a lot greater high quality. I used to be initially impressed by the precision of the primary board till I met quite a lot of difficulties associated to the inadequate solder masks (see under), however was completely impressed by the second model! The blue one is the JLCPCB one, the purple one is made by OSH Park.
The board is made round an MStar/SigmaStar MSC313E system-on-chip. This system is often present in IP cameras. It’s a very fascinating chip to make a small hand-solderable Linux-based pc, as a result of the RAM chip is built-in, so there are only a few pins (80) and it is available in a QFN bundle which is not as painful to cope with as BGA. Be aware that the 0.35mm pin pitch remains to be very small: pins are 0.18mm broad and spaced 0.17mm. The chip has fairly some connectivity, comparable to USB 2.0 (host/system), Ethernet with built-in PHY, that means that an Ethernet jack with built-in magnetics is all you might want to hook up with a community, SPI to entry a NOR flash for the working system, I2S for sound, and loads of GPIO. The chip itself could be discovered for ~$2.10/computer by 5, making it an interesting competitor to ESP32 and different WiFi-based chips each time TCP/IP is concerned, as a result of it’ll permit to run an actual working system with a strong software program stack.
It is seen that 1/4 of the board is utilized by decoupling capacitors and 1/4 by the DC-DC voltage regulation, so relying the place the chip is anticipated for use, it is perhaps potential to realize a lot smaller footprints if wanted (e.g. set up it inside a USB connector for instance).
The board comprises a USB-to-serial adapter, specifically a CH340E, in TSOP10 type issue, permitting to entry the SoC’s console from a PC. The identical micro-USB port that’s used for the console can be used to energy the board. I’d personally have wired it in another way, by powering the CH340E’s VCC from the USB connector, in order that the PC optionally powers the board. This might ease improvement by conserving the serial port frequently linked even when the board is powered down (from an exterior energy adapter or an onboard swap or jumper permitting to attach it to the micro-USB port). However it is a minor element.
The boot loader and working system are saved in an SPI NOR flash. This flash is 16 MB. For these fearing it is a bit tight, just a few distributors now present 32 MB fashions however uncommon are these capable of present it in SOP-8 type issue. A minimum of Macronix does with the MX25L25645G, although it is untested but. Past this there are SPI-NAND solutions storing as much as 512 MB however requiring a distinct driver as they could or might not emulate SPI-NOR. In any other case there are sufficient I/Os on the chip to connect an SD-card. However truthfully if you see this as a possible different to interchange an ESP32, 16MB must be manner ample for a lot of customers!
Assembling the board
Put together all the things
Let’s be trustworthy on this: assembling the board just isn’t for everyone, you might want to have fairly some expertise soldering SMD parts, to have the persistence to repair your errors and to not get discouraged if you worry you have fried one thing, since you will make errors. As well as you want just a few instruments:
- scorching air gun with controllable temperature and air move. You do not want the temperature to be correct (most will not be), you simply have to know find out how to set it to solder or desolder; just a little bit of coaching on an previous lifeless board may assist. Even a $30 one like mine is OK. Don’t even think about doing something proper with out this since you will not have the ability to desolder.
- good high quality tweezers. Mine are massive and delicate and not likely handy. Good ones should be very high quality on the edge and inflexible sufficient to completely maintain the parts. For instance these ones look right although I’ve not examined them.
- a great soldering iron with a high quality tip. Mine was 0.2mm when new, it is in all probability extra 0.4mm now. You want it to be lower than 0.5mm broad with the intention to selectively solder every 0402 element (0.5mm broad). A large one is considerable to take away extra solder across the SoC. A knife-shaped one could possibly be good.
- skinny and latest solder paste. Mine is sort 4 (25-38µm balls) and was just a few months previous, making it look thicker and fewer sticky. A greater one is sort 5 (15-20µm balls) in a syringe-like dispenser. That is arduous to seek out nonetheless, however I will present some methods under.
- some liquid flux in a syringe. The extra fluid the higher. You have to it to assist warmth small parts to put them appropriately, to scrub up the pads after you have badly tousled with a solder joint, to take away bridges between pins of the QFN chips, to take away extra solder from some joints, and so forth. Don’t even begin if you do not have some.
- a multimeter, with skinny probes.
- a magnifying glass, and if potential, a microscope. I do have a tiny crappy microscope like this one. It is mainly ineffective as you possibly can’t see additional than just a few mm deep so you possibly can’t examine solder joints. My digital camera nonetheless has a macro mode at ~5000 DPI (about 5µm per pixel) and is extraordinarily handy to intently examine the board.
- some isopropylic alcoohol (IPA) to scrub up the flux. If you cannot discover it, acetone additionally works however just isn’t pretty much as good, and smells quite a bit. IPA is odorless, and possibly much less poisonous.
- a toothpick or any skinny keep on with a 0.5mm tip that can be utilized to exactly deposit the solder paste. Do not use a needle, that is too skinny and the paste won’t stick with it. A nail may work although (not examined).
When you’re lacking some instruments, do not get too impatient, higher organize them and await them to reach than wreck your board.
Use a big nozzle with the new air gun
Opposite to what may appear intuitive when soldering 0.5mm broad parts, you will want a big nozzle on the new air gun. The one roughly as massive because the SoC is OK. The explanations for this are a number of:
- the solder paste won’t soften till the pads are scorching sufficient, which suggests the PCB itself should be scorching sufficient. With a skinny nozzle, it’ll take ages to warmth the PCB, and you may’t simply keep completely aligned with the pads you are targetting with out transferring;
- the decrease air move on the small one tends to encourage growing the temperature to get solder joints to really soften, however the greater temperature additionally ends in burning plastics when you will have connectors in your board;
- you’d suppose you can act individually on every element with a small nozzle, but it surely’s virtually the other. Normally there are only a few seconds of delay between adjoining solder joints begin melting, because it largely is dependent upon the PCB’s temperature. Nonetheless with a small nozzle, you will have a a lot quicker air move on output, which is able to shortly blow displace lightest parts and pack them collectively. On the other, with a bigger nozzle you will use a slower and softer air move that you just ship vertically. Many parts will then see their joints soften however they haven’t any motive for transferring beneath this gradual air move, and utilizing the tweezers you decide solely the one you are interested by.
- you will want a big one anyway for the SoC and also you definitely do not wish to attempt to change it whereas it is scorching.
Familiarize your self with the board format and print it
Put together all of the small parts
For many parts that are available rolls, there’s nothing extra annoying than completely switching instruments between the tweezers wanted to put the parts and no matter you utilize to peel off the rolls and decide one element at a time. An answer to keep away from this consists in checking the BOM (Invoice of supplies) first and put together as many of every sort as wanted. I like to put them on a sheet of paper beneath their reference, although the danger of transferring them away or mixing them is a bit excessive. They will also be positioned in small plastic packing containers and even in an ice tray. Be aware that values will not be marked on 0402 parts, so it’s essential to completely not combine them, otherwise you’ll want your multimeter to type them out. You’ve got been warned!
Put together the solder paste
Many individuals utilizing solder paste for the primary time imagine it is a chemical that turns to tin as soon as heated. That is unsuitable. It is manufactured from microscopic tin balls glued toghether in fats liquid similar to flux. That is seen within the following close-up of solder paste disbursed on a metallic plate. The second picture zooms on the primary one at approx 2.5 µm per pixel:
When heated, the liquid evaporates, releases solely the tin balls, which soften (if the temperature is excessive sufficient). Over time this liquid dries and grow to be thicker, a bit like wax, and loses of it sticking talents. It does not forestall the tin balls from melting, it is simply that it does not wish to stick with pads, forcing you to place quite a lot of it, and ends in large solder joints that bridge many pins without delay.
When you received it with a syringe, so long as it will get out of the syringe it is in all probability OK. When it is in a small pot like mine, you by no means know. And you do not even understand how lengthy it was saved on the vendor’s. A superb take a look at is to place a toothpick in it, and slowly pull. If it does not make a skinny wire, it is in all probability not sticky sufficient. And if the toothpick stays vertical as soon as planted simply in just a few millimeters, it is undoubtedly too thick.
However don’t worry, there are workarounds. A primary one is that if the paste is barely heated, it might probably grow to be fluid and sticky once more. For instance in case your soldering iron comes with a transformer block that is getting scorching, chances are you’ll go away the pot over it throughout all of the operations.
One other answer consists in re-injecting a little bit of recent flux into it. That is what I’ve received used to do now. It isn’t nice as a result of it does not final lengthy (i.e. 8 hours later it is thick once more) but it surely permits me to succeed in the extent of fluidity I need.
As a way to put together the answer, I simply decide just a few cubic millimeters of paste and place them in a metallic cup. Then I add 1/4 to 1/3 in quantity of flux and stir the combination till it turns into fluid and sticky. It takes time to get them correctly combined, you might want to be affected person. If it nonetheless does not stick, you possibly can add a bit extra flux, however watch out that it does not grow to be liquid. A superb take a look at is to make use of the toothpick, decide some and deposit it on a pad with out urgent. If it sticks that is OK. If it spreads like ink, you will want so as to add a bit extra paste to thicken it once more.
It may appear tempting to “repair” the entire pot of paste, but it surely’s not a good suggestion contemplating that the repair does not final lengthy: after just a few days you’d get a thick block once more and all you’d have achieved could be to waste quite a lot of flux.
Determine what technique you will use
There are no less than 3 strategies accessible at residence to solder the parts, and so they do not require the identical group.
Soldering iron
That is the primary technique I attempted. With a really high quality tip, it’s completely potential to solder all of the small parts. However let’s face it, this can be very tough. If the tip is not scorching sufficient the solder does not stick with the pads and if it is too scorching it oxidizes and the solder solely melts as massive balls creating bridges and you find yourself with one thing like under:
Yeah,there’s manner an excessive amount of solder there. The one manner I discovered to make this much less of a trouble was by utilizing solder paste on the primary of the 2 pads, soften it with the soldering iron tip, then place the element on high of it utilizing the tweezers, soften it once more, then use the soldering wire to make the second joint.
By no means ever tin the 2 pads without delay otherwise you will not have the ability to place your element flat! If some tin leaks on one pad from a earlier solder joint, restart with this one with out tinning the opposite one. If the primary of two joints leaks on a close-by pad, place the second element there earlier than making the second joint in order that within the eventuality the place the second joint will leak as nicely, you will not find yourself with two tinned pads for the subsequent element.
Given how shut all parts are to one another, it’s essential to course of them in the identical order, from the furthest to the closest of your hand in order that the tip by no means touches an already put in element. Regardless you will very seemingly trigger shorts that have to be inspected beneath a microscope and/or with a multimeter.
One other essential level to consider is to all the time begin from the thinnest parts and end with the tallest. A capacitor will hinder your entry to a close-by resistor and an inductor will make it even worse. You may observe that this generally contractics the earlier rule, particularly for the alternating resistors and capacitors which can be positioned above the DC-DC converter, which in all probability took me one hour to put in and repair.
Sometimes you need to use the new gun to rectify your parts alignment or smoothen the solder joints that present some spikes. You may have to recheck afterwards as a result of tall solder joints might spill over adjoining ones.
Scorching air gun
That is the second technique I attempted, primarily with a view to end what I could not realistically end with the soldering iron whose tip was oxidizing too quick. However the scorching air gun comes with its personal lot of challenges. You can not solder particular person parts with it, you solely function inside an space with out a lot precision, so that you spend your time heating what was already in place. When you blow too strongly, it’ll displace some parts and create packs which can be arduous to separate. Because of this it is higher to make use of a big nozzle with low velocity air than a small nozzle with excessive velocity air.
When you do not place a protecting metallic plate beneath your board, you will wreck your desk. I used an aluminum plate that got here from an previous CD participant for this. Nonetheless in case you place the board instantly on the aluminum, it won’t warmth, which is the rationale why I inserted a small piece of plywood between them, and connected all the things utilizing Kapton tape.
One other difficulty with the air gun is that you might want to be very exact in the best way you place the solder paste, as a result of in case you go away some on a close-by pad, it’ll soften and make it tough to later place a element. So you must proceed in teams of parts, or aggregates. It isn’t all the time simple to proceed like this, as a result of every element is shut to a different one so it is not all the time easy to delimit aggregates. That is what I attempted on the primary board captured within the images under with solder paste that was too thick and thus too ample, inflicting some parts to maneuver and a few bridges to look:
On this board it’s potential to proceed like this, however no matter is across the DC-DC regulator is diffcult to separate into small areas. Resulting from this, the temptation could be excessive to put all parts without delay and attempt to solder all of them in a single go. And this isn’t a nasty answer in any respect!
When you go this fashion, I might recommend that you just first place all capacitors, all resistors, and the LEDs, and proceed with all of those. Then you possibly can add the inductors and the crystal oscillator, then the DC-DC, regulator. At this level you possibly can mark a break, confirm all of your solder joints, test for shorts between close by parts (notably resistors which can be very near capacitors and which have a tendency to maneuver), and you may join a current-limited 5V PSU to the J1 connector and confirm that you’ve the anticipated voltages on numerous take a look at factors, 3.3V, 1.8 and 1.0. In any other case you might want to debug. As soon as that is OK you possibly can add the CH340E USB-serial chip, the micro-USB connector and take a look at once more. As soon as OK you simply need to solder the SoC, the flash chip, and flip the board to solder the three 0R resistors and a couple of capacitors. Don’t set up the ethernet jack earlier than the board is proven to work, as it will likely be an actual ache to later solder/desolder.
Oven
No, I am not speaking about shopping for a reflow oven, nearly utilizing your kitchen’s oven. I’ve executed this many occasions already, together with to repair points beneath BGA chips, and it has grow to be my most popular technique, being simpler, quicker, and extra correct. You simply want a thermometer to determine what temperature roughly to make use of, as a result of as you possibly can guess, the displayed temperature does not match in any respect the one within the oven, and whereas 10% distinction are in all probability not essential for cooking, they will make an enormous distinction for soldering. I discovered that mine heats to about 260°C when it shows 230, and that temperature is ideal for melting solder paste. If in case you have a number of settings, desire these with circulating scorching air as an alternative of these with a high infrared resistor: the latter one tends to warmth black areas far more. Additionally it is very handy to have a rotating plate.
The working mode that works finest for me is the next: I first place all of the parts like for the new air gun, besides the QFN chips since I do know I will have to repair them afterwards anyway, and besides the USB connector with a view to shield it in opposition to the danger of melting. I then place a small ceramic dish within the oven to carry the PCB, and pre-heat the oven till my thermometer exhibits it reaches about 260°C. Then I open it, I fastidiously place the PCB onto the dish, and let it cook dinner for 4-5 minutes in circulating air mode.
Be very cautious to not accidently allow microwaves! In case your oven reaches the next temperature, cut back the length. As soon as the time is over, I open it once more and take a look on the solder joints. It is potential they have not melted but, wherein case solely the flux will probably be gone and you will see loads of small shiny tin balls. On this case, cook dinner it once more for an additional 2 minutes and examine once more, solder joints ought to be easy and glossy:
As soon as that is executed, I cease the oven and it mechanically enters a calm down section which lasts a couple of minutes. After that the circuit remains to be extremely popular however could be picked utilizing tweezers or by putting a knife beneath, and you may examine it.
Some parts may have moved, don’t be concerned about that. Normally these with unequal quantities of solder paste on their pads will transfer. However total it is lower than 10% of them which get displaced.
Examine very fastidiously as a result of some parts might flip 90 levels and look regular:
Set up the DC-DC regulator
The EA3036 in all probability is essentially the most tough piece to put in. There isn’t any clearance to function round it, and being very small, its very mild as nicely and floats on high of melted tin. As such, in case you put an excessive amount of solder, its pins won’t make contact, as could be seen under. The worst half was when eradicating it and found a considerable amount of tin!
I discovered that you might want to put virtually no tin on the bottom aircraft beneath it, a lot lower than a cubic millimeter! Simply put the minimal you possibly can. One strategy consits in simply touching the bottom aircraft with the tip of your soldering iron, and eradicating extra solder utilizing solder wick, making an attempt to not pull off the tracks. An alternate is to try this on the chip itself. Additionally, if you solder paste could be very fluid, you possibly can simply go away a small drop.
The second problem is to determine how a lot solder paste is sufficient, and the way a lot is an excessive amount of. I discovered that “portray” the pads with a toothpick impregnated with solder paste, making 4 skinny, 1mm-wide, threads of paste passing by the middle of the pads, gave finest outcomes. When you worry your paste is just too liquid, dispense some on the chip’s pins earlier than putting it. So long as the solder amount is nicely balanced between the 4 sides, the chip won’t transfer and you may warmth it vertically utilizing the new gun. As soon as executed, examine it utilizing a microscope. There’ll seemingly be shorts, particularly with the model 1 board, don’t be concerned for that, you will simply take away them utilizing flux and the tip of your soldering iron:
What issues is to ensure the chip touches the PCB and is flat on it. If not, you will have to warmth it once more and presumably to press over it utilizing your tweezers. If it resists, it means you have put an excessive amount of paste beneath it and you will have to take away it, clear it and place it once more.
Additionally double-check that the chip is nicely aligned. For instance under, after it went by the oven, the regulator turned just a little bit and displaced by one pin on two sides. But it surely’s additionally potential that it is merely shifted by one pin, which isn’t all the time simple to identify. Thus be very cautious, and repair it if wanted:
Oh and by the best way, after fixing the alignment of the chip above, I noticed it was incorrectly turned so I needed to desolder and solder it once more after rotating it. By the best way, whereas it was once very tough to not have shorts beneath the chip on the model 1 board, I by no means had any failure when desoldering and resoldering it on the brand new board!
As soon as the chip touches flat on both sides, you possibly can take away the bridges that presumably exist between some pins. Simply dispense some flux on both sides, and utilizing your soldering iron tip, gently sweep both sides by urgent in opposition to the chip just a little bit. This can re-melt extra solder which is able to deposit in your tip. Clear the tip and repeat for an additional aspect. On the finish the chip will probably be completely soldered with no bridge between pins.
Preliminary assessments with out the SoC
I discovered that it is higher not to solder the SoC first. It reduces the danger of frying it and frying the voltage regulator. Similar with the CH340E that is powered from the 3V3 output. For this reason I desire to solder all passives and the DC-DC regulator first, then take a look at.
First, find the 1.0V, 1.8V, 3.3V and 5V factors, and confirm utilizing an ohm-meter that they are neither shorted to the bottom nor shorted collectively. A brief to the bottom might point out a brief beneath a capacitor or bleeding resistor. A brief between one another signifies a brief within the uncommon locations the place they arrive shut to one another, very seemingly within the capacitor row on the backside of the board, under the SoC. As soon as that appears OK, it is time to take a look at.
Mine
is proscribed to about 250 mA max, which is sufficient to shield the DC-DC
regulator for a short while. If you have not but soldered the micro-USB
connector, simply minimize a USB cable and join the purple and black wires to
the +5V and GND pins under. When you’ve already soldered the micro-USB
connector, merely join it utilizing a daily cable to the present
limiter. I most popular to not solder the connector too early as a result of it is
simpler to solder the CH340E when the connector just isn’t there.
Whenever you discover the voltages are OK, it is the second to put in the CH340E and the micro-USB connector. The CH304E is the second best system to put in (the simplest one being the crystal oscillator). With the correct quantity of solder paste, it’ll align completely with no effort, even utilizing your soldering iron if you’d like.
The micro-USB connector is much less simple to solder as a result of it might probably additionally float on the paste you will place on the bottom aircraft. Thus watch out and like so as to add some additional later than placing an excessive amount of initially. If there’s an excessive amount of paste, it could brief with the +5V pad beneath the connector (pin1 on the high). It is smart to confirm there isn’t any such brief with an ohm-meter earlier than connecting once more. As soon as linked once more, the system will drain about 2.4 mA if the chip works. Connecting it to a PC will present a USB-serial port if all the things works. When you get USB errors you may need a brief between one of many DM or DP pins and the bottom (or between one another).
Set up of the SoC
The SoC is completely scary. It has a 0.35mm pitch, its pins are 0.18mm broad and there is solely 0.17mm spacing between them. How is it potential to solder this by hand, you’ll marvel? Simply belief your abilities and do it! It is simpler than it seems to be! Identical to for the EA3036 DC-DC regulator, I discovered that portray 4 skinny threads of solder paste over the pins on both sides and doing the identical on the chip earlier than putting it really works fairly nicely:
I discover it handy to additionally put a little bit of paste on the chip itself and a few flux on the bottom aircraft. That is notably helpful after changing the chip as a result of the board just isn’t completely easy anymore and this enables every pin to begin to grip the pads. It was largely needed for the v1 board, the v2 is of significantly better high quality and I’ve made one with no need this:
Nonetheless I do have just a few warnings to say:
- the chip is massive. Properly, by “massive” I imply that it has many pins per aspect (20) and that it’s completely essential that the paste is evenly unfold between them on both sides. If that is not the case, some pins won’t be linked and you will have to desolder it and check out once more. Be very cautious about this.
- solely maintain the chip utilizing the tweezers. It has nothing to do with static electrical energy, it is simply that in case you maintain it utilizing your fingers, and put some paste on the chip itself, you could be sure that you will put them within the paste in some unspecified time in the future and make some areas uneven.
- put little or no paste on the bottom aircraft, lower than one cubic millimeter, or the chip won’t contact on the edges. Worse, the bottom aircraft acts like a warmth spreader and as soon as soldered it will likely be very arduous to soften it once more or take away any extra solder:
- completely align the chip earlier than heating. When the solder paste is positioned, you will not see the alignment factors anymore. Do not confuse the strains used to indicate capacitor areas with alignment factors, they are not the identical. In case of doubt, be certain that there’s a fair pad width on both sides and you will be high quality.
- in case you put an excessive amount of solder paste on the pads, for instance if there may be some paste making bridges with the bottom aircraft, higher wipe it and check out once more.
- don’t wait too lengthy after you have positioned the paste, particularly in case you diluted it with flux, as a result of it’ll progressively spill and broaden.
As soon as correctly positioned, warmth the SoC vertically utilizing the new air gun, and be affected person. Ensure the PCB just isn’t instantly in touch with chilly metallic, as the warmth from the bottom aircraft may unfold into it and forestall the solder from melting. As soon as the solder paste melts, you might even see the alignment marks once more. When you do not see them, it means they’re completely beneath the chip. If the chip is correctly aligned, the pads will look even throughout. If in case you have the slightest doubt, don’t be concerned, it means it is OK, as a result of when it is unsuitable it’s very apparent, with 0.7mm distinction in clear space between two sides.
Now’s time for visible inspection utilizing a microscope. If any pin seems to be disconnected (the pad seems to be like there’s little or no solder on it), you possibly can strive your luck by filling the opening utilizing solder paste and melting it once more, but it surely’s seemingly that you will have to desolder and resolder.
As soon as OK, you will simply have to scrub the bridges. Don’t worry if what you begin with seems to be terrible like this (these chips had been changed a number of occasions as a result of misconnected pins and the surplus of solder begins to be fairly seen):
Dispense some flux throughout the chip, and slowly wipe it with the tip of your soldering iron in a single course from one nook to the subsequent one. It is going to soften the solder beneath the tip and take away the surplus that may stick with the tip. Simply clear the tip after every cross. A knife-shaped tip is best for this operation however just isn’t necessary.
You may have to visually examine it once more utilizing a microscope, and you might have to scrub up the surplus flux utilizing isopropylic alcoohol or acetone. I used to put the board in a glass and pour a little bit of alcoohol on high then jiggle it for a couple of minutes:
A fast inspection after this exhibits that it is significantly better:
Be aware that there are two locations the place adjoining pins are linked collectively and these will not be brief circuits.
Set up the flash
As anybody who engages in an digital circuit, you have learn the entire doc earlier than beginning, did not you ? 🙂 So you recognize it might probably take one hour to program the flash and that it had higher been executed previous to ending.
I programmed mine utilizing a Buspirate board, and it is certainly extraordinarily gradual (1 hour). It may be even twice as gradual in case you allow confirm. The annoying half is that it does not work to program the flash in-circuit, so you really want to flash a working picture earlier than soldering it, and if it does not work you will have to desolder it and repair it.
The flash is fairly simple to put in. Simply tin one pad on the board, then utilizing tweezers, you place the chip whereas conserving the pad scorching, till all pins are completely aligned with the opposite pads. Then you definately simply have to solder the opposite pads and that is executed.
You possibly can clear the board, in case you’re fortunate you are executed with this aspect 🙂 Does not it look superior for one thing home-made ?
Fast take a look at
When all that is put in, you possibly can hope to begin to talk with the SoC. Find the C38 capacitor on the backside proper under the SoC, it is the one used to reset the board. The reset pin is the one on the backside, linked to the R23 resistor. Utilizing your tweezers you may make a contact throughout the capacitor to reset the SoC once more. Be extraordinarily cautious, the highest pin is linked to +3.3V and the capacitor subsequent to it’s linked to 1.0V, in case you brief the 2, you will fry the chip. Simply practice your self with the board disconnected first.
Then join the board to your PC by the present limiter and presumably a present meter. Open a serial terminal at 115200 bps and observe. You seemingly will not see something. Simply reset the board utilizing the tweezers as indicated above. You might even see a greeting message talking about IPL and HW RESET. That is beginning to get nice, is not it ? 🙂
The board ought to be consuming about 80-100 mA at this level:
If it consumes a lot much less (round 10mA) in all probability it is caught in reset. Re-check all voltages and confirm that the reset pin is not pulled up, e.g. as a result of a brief with one of many console pins. You can even test with an oscilloscope that you just see a 24 MHz sign on the crystal oscillator pins. If it nonetheless does not do something regardless of all voltages being good, it could point out that there are nonetheless some dangerous solder joints under the SoC and that you will want to repair them.
Now’s time to complete
Disconnect all the things, flip the board, solder the three 0R resistors (R11, R17 & R12), and the 2 capacitors C33 & C34:
Solder the Ethernet jack, and also you’re executed.
Your new pc ought to boot and greet you with a console. Be aware that by default U-Boot waits as much as 10 seconds so the board might stay silent for 10 seconds after displaying some rubbish. That is anticipated.
If issues go unsuitable
I ought to have titled this “when issues go unsuitable” as a result of issues will go unsuitable. A number of of the potential points are listed right here.
Brief circuits
The primary points I met with the preliminary JLCPCB board was that the solder masks was inadequate and there have been no safety between adjoining pads. There have been numerous shorts in all places. I needed to desolder and resolder the USB-serial chip 5 occasions, the micro-USB connector 3 occasions, the SoC 6 occasions and the DC-DC 8 occasions, all of this due to shorts beneath them. In such a scenario there is no different answer however visible inspection utilizing a microscope, and placing the smallest potential quantity of solder paste beneath the chips, and most of it in seen areas in order that extra solder goes the place you possibly can decide it. Luckily with the newest variations of the PCB, the solder masks is great, essentially the most correct I’ve ever seen, and this downside hasn’t occurred any single time in any respect. Nonetheless there can nonetheless be shorts between pins on the CH340E chip and between close by parts.
For the CH340E chip, one of the simplest ways to take away skinny shorts is to place some flux and use a clear soldering iron tip. The tin will soften and repair by itself. If there’s an excessive amount of tin, or in case you accidently add some along with your tip, you will have to take away it utilizing solder wick. The tiny brief under between pins 2 and three is kind of scary given how skinny it’s, it was solely seen in macro mode, however not beneath the magnifying glass. And it prevented the chip from working. Luckily this can not occur anymore with the brand new boards:
Be extraordinarily cautious with solder wick, it is all the time with this that copper tracks get pulled off, like right here:
By no means pull it if it does not wish to come, it means some solder managed to chill down, and that you might want to correctly warmth it up till it comes by itself. General it was wanted with the model 1 of the board because of the quite a few shorts and the unfinished solder masks, however with model 2 I by no means wanted it.
For close by parts like a resistor and a capacitor, let’s first test on the board format if they’re supposed to the touch or not, as a result of a lot of the adjoining ones have pads in frequent and truly contact solely due to this. If they don’t seem to be supposed to the touch, you will have to separate them. More often than not I strive with the iron as a result of I imagine I can, but it surely’s all the time a multitude. You possibly can’t add extra solder since there’s already an excessive amount of, and you may’t warmth each side of the element with out including some. You find yourself making the element very soiled or displacing different ones. The cleanest technique consists in patiently heating the realm utilizing the new air gun positioned vertically over the element at a low air move price, and ready for its joints to soften with the intention to decide it utilizing your tweezers. It might occur that it’s going to include the opposite one it was connected to. It isn’t dramatic, simply decide them each and separate them (this time the iron may make this simpler). Take away the surplus solder, clear them up and place them once more.
Misoriented parts
Just for just a few parts the orientation issues: the 4 built-in circuits and the two LEDs. For all passives you do not care, neither do you for the crystal oscillator. The inductors require a little bit of care, as a result of they appear completely sq. from above however solely assist 2 positions out of 4, so higher double-check when putting them.
When you determine that you just misplaced a element, you will have to desolder it utilizing the new air gun, clear its pins, clear the pads, and solder it once more. Be aware that it is precisely what occurred to me with the EA3036 on the final board, I received a bit too assured when soldering it, and fortuitously I rechecked earlier than plugging. If you might want to desolder and resolder the EA3036 or the MSC313E, chances are you’ll have to put some paste on the chip’s pins to compensate for the roughness of the board as a result of solder residue, as proven under:
For LEDs, you’d relatively test along with your multimeter first. Many have a diode place permitting you to identify the + (anode) and – (cathode). Watch out in case your multimeter solely has a resistor place, as lots of them have their polarity reversed in ohm-meter mode, so higher double-check on a recognized diode first. In any other case you need to use a battery and a 1k resistor to determine the LEDs polarity.
Unsuitable voltages
If two voltages seem an identical and match an accurate one (e.g. 1.8V), you seemingly have a brief between their outputs. 1.0V and 1.8V outputs are very shut to one another at a number of locations, and 1.0 and three.3V as nicely, particularly within the capacitors space under the SoC.
If two voltages seem an identical and do not match any recognized one (e.g. 1.5V or 2.4V) you seemingly have a brief between their suggestions sensing circuits. This more than likely issues the 1.0V and three.3V which can be within the LED space on the high of the circuit.
If an output exhibits virtually 5V it could point out {that a} suggestions resistor is not correctly linked, that the pin is tied to floor, or that the equal suggestions ping on the DC-DC regulator does not correctly contact its pad. You may have to find it on the schematic and discover it on the format to confirm.
If an output exhibits 0V, it may point out that the output pin of the DC-DC regulator does not correctly contact its pad, that the suggestions pin is shorted with an influence pin, or that the output pin is shorted with floor (making the inductor warmth up in a short time).
If voltages look inverted, or two voltages appear unsuitable, with one too excessive and the opposite two low, it is very seemingly that you’ve got combined up suggestions resistors, so you will need to recheck them.
The system does not begin
The yellow LED (high left) ought to mild firmly when issues are OK. When you do not see it activate or in case you observe only a faint glow in the dead of night, the chip doens’t boot. For instance it simply stops on “IPL” or “HW RESET”. This might point out it does not see the flash (poor connections, dangerous contents), does not see its inside DDR (dangerous connection beneath the VDD pins on the high left nook of the SoC) or that among the 0R resistors are lacking on the opposite aspect.
The system shows output however takes no enter
This simply seems to be like a brief on the Rx pin of the SoC or a misconnected pad, look beneath the underside proper nook.
Some chip heats quite a bit
That is not anticipated. The EA3036 stays barely heat to the contact, the flash and the USB adapter are completely chilly, solely the SoC heats up. One thing heating up might point out a brief circuit or a lifeless element, don’t let the facility linked too lengthy when checking, and keep away from connecting it to your PC!
Did I kill that chip ?
I fried two regulators and one SoC with the primary technology of boards that introduced me tons of shorts, and I did not have my present limiting circuit. Apart from that, the parts resist extreme abuse. Let me give just a few examples:
- EA3036 desoldered/resoldered 8 occasions
- SoC desoldered/resoldered 6 occasions. Stored at 650°C for greater than 30 seconds no less than as soon as when it refused to desolder (the PCB began to show barely brown).
- SoC wrongly powered on 1.8V a number of occasions as a result of shorts between 1.0 and 1.8V. The DDR controller lastly died when 1.8V and three.3V had been shorted for an prolonged time frame, however the SoC continues to reply to reset.
- flash could be desoldered/resoldered many occasions with out loosing contents
- crystal oscillator fell on the ground with no injury
So in case you’re not seeing one thing working, it is pure to marvel in case you did something unsuitable that may have resulted in killing the chip. However I might say it is extraordinarily unlikely, even with repeated errors. So long as the voltages are current on output, the DC-DC regulator does its job. So long as the 24 MHz crystal exhibits a sign, the SoC is not fully lifeless. You’d relatively desolder, clear the pins and resolder than contemplate you killed one thing.
What could be executed with that board
The board remains to be in lively improvement, Daniel received quite a lot of his patches built-in into kernel 5.9, and the remaining ones will hopefully be in 5.10. His improvement branches work fairly high quality for each day use already. As such, in its present state, this board permits to do no matter could be executed with a pc having 64 MB RAM and an Ethernet port. It may be a small proxy, SSH bounce level, VPN gateway, sensor for numerous stuff, and so forth.
As well as Daniel has already made some breakout boards for micro-SD playing cards, GPIO and USB connectors. For instance with a USB-OTG port, the cardboard may grow to be a wise USB-ethernet port, that includes web connectivity by way of a VPN. With I2S and micro-SD it could possibly be used as a music participant. It is also built-in right into a digital music instrument to document/play MIDI information saved on a distant pc.
There may be additionally a WiFi breakout board supporting small and cheap USB WiFi playing cards, opening the sector of IoT, the place this board can grow to be far more fascinating than the common ESP32 gadgets:
There are numerous potentialities the truth is, and seeing that because of Daniel’s work now you can construct your individual Linux pc your self opens much more potentialities.
Views
Truly whereas I wasn’t initially a lot interested by taking part in with that board since I did not have a direct use for it, I figured it may make an excellent possibility for our subsequent technology ALOHA Pocket at work. It is extra highly effective than the earlier one made out of a GL.iNet 6416A, will work with a mainline kernel, which is able to ease our port, and actually seems to be like an awesomely geeky system! A minimum of I used to be curious sufficient to attempt to boot the ALOHA on it and it labored fairly nicely 😉
I am fairly certain there are many usages to be present in residence automation. Let’s simply join the WiFi breakout board and a contact show over SPI to see what could be executed. At present equal gadgets run on microcontrollers with restricted and even insecure HTTP/TCP stacks. Right here you may have a full blown HTTP/REST/H2/gRPC/MQTT/QUIC/no matter over TCP/TLS and the usual instruments you utilize every single day to program your property purposes. Plus you may ssh into your system to improve or debug it.
Enhancements
Daniel is taking a look at different chips of the identical household. Some have extra RAM, extra cores, extra MHz, and so forth. I believe that within the present state, the one trivial enchancment could possibly be to double the NOR flash measurement and/or so as to add an SD card adapter. It is fascinating to comply with Daniel’s work on the kernel, because the chip helps a watchdog, some crypto extensions, a {hardware} RNG, sound and loads of different stuff. There’s nonetheless some work to do, and you may assist by testing the development code and giving suggestions to Daniel.
Closing phrases
Not solely I wish to thank Daniel for sending me this equipment and making me push my soldering abilities past the earlier limits, however I actually wish to congratulate it for this totally superior mission. I am keen to assist him as time permits to assessment and take a look at code. We actually want such initiatives to scrub the present state of the IoT world by deploying clear and safe working programs. And such boards are improbable for schooling. I’ve already purchased extra packs of parts to provide away and let others make their very own boards in flip, hoping this may grow to be viral 🙂