Starting with my first SBC Project, Plans and Confusions

[GARTHWILSON]

Proxy wrote:

I don't know why it wouldn't work. maybe i killed the chip somehow? the soldering didn't take too long and i used ~250°C with the iron. i tried not to be on the pins/chip for too long

The chance of damaging the IC with soldering-iron heat is just about zero. In a job I worked in 1984-85, I sometimes used an infrared microscope to thermal scan power transistors' uncovered dice (ie, the actual chips) operating under extreme loads, and I've seen them actually operating (not just in storage or in soldering, but operating) at over 350°C. I don't know how far over, because I wasn't allowed to get calibration data any higher. Granted, they would not have lasted long, but it did not cause catastrophic failure.

Quote:

also i looked online and people really don't recommend using acetone on electronics. example

Acetone will not remove the soldermask. I've soaked a little board in acetone for days with no perceivable effect on the green soldermask. BDD recommended the acid brush though because acetone may dissolve a toothbrush's plastic bristles and turn them to gum. I wouldn't use nail polish remover since it usually has cuticle conditioners and things that might leave an undesired film on the board.

Good luck on getting it all going. We all have a forehead-slapper experience here and there over the years, a problem that holds up progress for days but which we would have caught in an instant if we had just opened our big eyes and looked right at it.

[BigDumbDinosaur]

GARTHWILSON wrote:

We all have a forehead-slapper experience here and there over the years, a problem that holds up progress for days but which we would have caught in an instant if we had just opened our big eyes and looked right at it.

Yep!

[BigDumbDinosaur]

Proxy wrote:

also i looked online and people really don't recomment using acetone on electronics.

Uh-huh. One of the posters on that site said, "Check a pharmacy for rubbing alcohol, I would not use acetone." Obviously, that was posted by someone who doesn't know what is in rubbing alcohol:

Quote:

The United States Pharmacopeia defines 'rubbing alcohol USP' (the most commonly-sold form of rubbing alcohol in North America) as containing approximately 70 percent by volume of denatured alcohol.

If rubbing alcohol consists of 70 percent alcohol, just what comprises the remaining 30 percent? Some of the chemicals are bitterants used to make the alcohol unfit for consumption. Lanolin is often part of the mix to make rubbing alcohol less irritating to the skin. Do you want to put lanolin and other (possibly unknown) chemicals on your electronics?

Another individual writes, "Acetone is a great way to remove all of the coatings from your PCBs..." That's unadulterated nonsense. I have never seen that happen, and as I earlier said, I've been working with this stuff for decades. The solder mask that is applied to PCBs is very tough.

Anyhow, you can't believe everything you read on the Internet.

[Proxy]

ok i see, stupid internet....

so i choose some acid brushes on amazon, now i just need acetone.
and nail polish remover wouldn't work? even when it literally says "100% acetone" in the ingredients?
I'll check my local hardware store later today

[Proxy]

After searching a bit online I found a datasheet from FTDI talking about the hardware requirements/tips for USB.
https://www.ftdichip.com/Documents/AppN ... DI_ICs.pdf
It says some things I didn't think about when designing the PCB.

Maybe I'll redo the placement of the chip to be closer to the USB port, use SMD resistors for it (since they're smaller), and have a continuous ground plane under the USB traces (though I don't know how that would work since the USB port is TH and therefore cannot have a ground plane directly below the pins)

But I'll still ask on reddit to see what other people think, since it's more likely they know of these modern interfaces.

[cjs]

Proxy wrote:

But I'll still ask on reddit to see what other people think, since it's more likely they know of these modern interfaces.

I'm guessing that the EEVblog community forum might also be a good place to ask. There seem to be a lot of very knowledgable people there.

[BigEd]

Proxy wrote:

ok i see, stupid internet....

so i choose some acid brushes on amazon, now i just need acetone.
and nail polish remover wouldn't work? even when it literally says "100% acetone" in the ingredients?
I'll check my local hardware store later today

In a case like this, I'd believe the ingredients. (However, I'd be wary of acetone - despite the reassurances and warnings upthread. The thing is, you can't believe everything you read, internet or otherwise, even here.) I've got some isopropyl alcohol, which is sold for the purpose of cleaning electronics.

[Chromatix]

Isopropyl is commonly sold as lens or tape cleaner. If VCRs are still commonly used in your area, look for VCR cleaning kits. Otherwise, visit an optician or a camera shop if you can't find it in the supermarket.

[Proxy]

cjs wrote:

Proxy wrote:

But I'll still ask on reddit to see what other people think, since it's more likely they know of these modern interfaces.

I'm guessing that the EEVblog community forum might also be a good place to ask. There seem to be a lot of very knowledgable people there.

I'll try on there, thanks.

As for isopropyl, I already got 1L bottle of 99% isopropyl (thanks to Amazon), which I used to clean the flux off the the back of the board, I also used it to clean the SMD chip.

Either way I likely have to redesign the USB part of the board anyways so sadly I have to reorder new boards and wait even longer...

[BigDumbDinosaur]

Proxy wrote:

ok i see, stupid internet....

so i choose some acid brushes on amazon, now i just need acetone.
and nail polish remover wouldn't work? even when it literally says "100% acetone" in the ingredients?
I'll check my local hardware store later today

First off, it would be helpful if you would add your geographic location to your user profile. Knowing that often helps in others advising on the procurement of various products.

As for nail polish remover, it is not 100 percent acetone, no matter what the label says. Pure acetone is an irritant that can be absorbed through the skin and cause a variety of medical issues if one is frequently exposed. For that reason, and others, consumer nail polish remover is typically a solution of acetone or ethyl acetate (one or the other, with the latter more common these days), propylene carbonate, toluene and lanolin (or a lanolin-like equivalent). The lanolin is there to counteract the skin-drying effects of the base solvent—acetone or ethyl acetate.

If you use nail polish remover to deflux your PCB you will be applying chemicals that may have an unknown effect on both the board and components. Acetone used for solvent purposes is "technically pure", meaning it is nearly 100 percent solvent with no additives of any kind (practically speaking, "technically pure" implies 100 percent purity, which is unattainable). That is what you should be using. A hardware store or paint dealer are good sources. A small can of acetone will last for a long time if kept sealed when not in use. Naturally, you should take steps to avoid contamination.

[cjs]

Proxy wrote:

what doesn't works is the FTDI USB Chip. my PC sees that there is a USB Device but it aparently cannot read what it is from the device... which is strange

Proxy wrote:

Either way I likely have to redesign the USB part of the board anyways so sadly I have to reorder new boards and wait even longer...

Looking at the device data sheet, I notice two things.

First, it's not a particularly high-speed device, even by '80s standards. It uses USB 2.0 full speed, 12 Mbps. I'm not convinced that a slightly suboptimal layout of it would cause serious problems. (I suspect that the document you were looking at about layout etc. may be more about USB 2.0 high speed, which at 480 Mbps is something where I'd imagine those kinds of layout techniques do make a noticable difference.)

Second, it looks as if it may not be implementing any of the standard device classes that would allow most OSes to immediately let you start using the device. The data sheet says, "FTDI’s royalty-free Virtual Com Port (VCP) and Direct (D2XX) drivers eliminate the requirement for USB driver development in most cases." Given that they supply their own drivers for "com port" and bulk data transfer, it would be reasonable that they wouldn't bother also to implement other standard protocols that are either less suitable (USB block storage device) or annoyingly slow (USB serial) for the application.

I would carefully debug the existing board before ordering a new one. (It would be particularly frustrating to re-spin the board only to find the same problems!)

• If you're using Windows, make sure the correct drivers from FTDI are installed. Use any debugging tools they supply.
• You can plug the board into a Linux box and see what the kernel messages say about it. If it successfully attaches a generic device, you can use command line tools such as lsusb to get more details about exactly what it found, including device and endpoint descriptors.
• If Linux fails to attach even a generic device, try different cables and, if that fails, get a 'scope on to the D+ and D- lines (both ends!) to see what's going on there.
• Using either Linux or Windows, you can write small programs using libusb to poke at and probe the device to see how far you can get with communicating with it.

Obviously all of this is going to require some knowledge about how USB works. I have seen a great set of pages on this that could get someone at your level up to speed in no time flat, but I can't find the darn things now. :-( But this article is short and might be fairly useful, and it also is probably worth at least scanning through the info on Wikipedia. I'll try to find better resources as we go along.

[Proxy]

BigDumbDinosaur wrote:

Proxy wrote:

ok i see, stupid internet....

so i choose some acid brushes on amazon, now i just need acetone.
and nail polish remover wouldn't work? even when it literally says "100% acetone" in the ingredients?
I'll check my local hardware store later today

First off, it would be helpful if you would add your geographic location to your user profile. Knowing that often helps in others advising on the procurement of various products.

As for nail polish remover, it is not 100 percent acetone, no matter what the label says. Pure acetone is an irritant that can be absorbed through the skin and cause a variety of medical issues if one is frequently exposed. For that reason, and others, consumer nail polish remover is typically a solution of acetone or ethyl acetate (one or the other, with the latter more common these days), propylene carbonate, toluene and lanolin (or a lanolin-like equivalent). The lanolin is there to counteract the skin-drying effects of the base solvent—acetone or ethyl acetate.

If you use nail polish remover to deflux your PCB you will be applying chemicals that may have an unknown effect on both the board and components. Acetone used for solvent purposes is "technically pure", meaning it is nearly 100 percent solvent with no additives of any kind (practically speaking, "technically pure" implies 100 percent purity, which is unattainable). That is what you should be using. A hardware store or paint dealer are good sources. A small can of acetone will last for a long time if kept sealed when not in use. Naturally, you should take steps to avoid contamination.

Sorry I though I added the location when I made the account. Fixed now.

And yea I get it, when I get acetone I'll just get it from a hardware store.

Anyways I'll be testing the computer later today, just because the USB interface is not working doesn't mean the rest of the computer is broken as well.

I already hooked up an 8 bit D-FF as IO device (0xDFFF) that I should be able to output data to... but I ran into some problems I need to further check later.

[BigDumbDinosaur]

Proxy wrote:

Anyways I'll be testing the computer later today, just because the USB interface is not working doesn't mean the rest of the computer is broken as well.

I suspect your PCB layout has no bearing on the operation, or lack thereof, of your USB port. In a lot of these cases, barring an outright design error or a "wiring" error on the PCB, it turns out to be an interface error, e.g., mismatch bit rates, mismatched data format, etc.. That is to say, you may have another "head slapper" situation.

[Proxy]

cjs wrote:

Looking at the device data sheet, I notice two things.

First, it's not a particularly high-speed device, even by '80s standards. It uses USB 2.0 full speed, 12 Mbps. I'm not convinced that a slightly suboptimal layout of it would cause serious problems. (I suspect that the document you were looking at about layout etc. may be more about USB 2.0 high speed, which at 480 Mbps is something where I'd imagine those kinds of layout techniques do make a noticable difference.)

hmm, i did read about that on StackExchange, i still thought my design would be a problem because the traces are around 3cm long and go through a TH Resistor each.

cjs wrote:

Second, it looks as if it may not be implementing any of the standard device classes that would allow most OSes to immediately let you start using the device. The data sheet says, "FTDI’s royalty-free Virtual Com Port (VCP) and Direct (D2XX) drivers eliminate the requirement for USB driver development in most cases." Given that they supply their own drivers for "com port" and bulk data transfer, it would be reasonable that they wouldn't bother also to implement other standard protocols that are either less suitable (USB block storage device) or annoyingly slow (USB serial) for the application.

I did install the FTDI drivers before connecting it, it still gave the "device descriptor request failed" error message.
i assume if the chip wouldn't respond/work at all it just wouldn't show up in the device manager. (like any non data transfering USB device does)
Which is the reason I think that there is a problem on the PCB as even without drivers it should still show up as an unknown device (with Hardware ID and everything) without any errors.

cjs wrote:

I would carefully debug the existing board before ordering a new one. (It would be particularly frustrating to re-spin the board only to find the same problems!)

I checked all pins twice, with help of the datasheet, and all connections look and measured correctly (also no shorts between pins), I made sure the D+ and D- lines are correct and not switched around.
if this picture is accurate then i got the D- line connected to Pin 14 (USBDM) and D+ connected to Pin 13 (USBDP), which should be the right way around (acording to the datasheet)

Untitldsaed.png (217.9 KiB) Viewed 1843 times

cjs wrote:

• If you're using Windows, make sure the correct drivers from FTDI are installed. Use any debugging tools they supply.
• You can plug the board into a Linux box and see what the kernel messages say about it. If it successfully attaches a generic device, you can use command line tools such as lsusb to get more details about exactly what it found, including device and endpoint descriptors.
• If Linux fails to attach even a generic device, try different cables and, if that fails, get a 'scope on to the D+ and D- lines (both ends!) to see what's going on there.
• Using either Linux or Windows, you can write small programs using libusb to poke at and probe the device to see how far you can get with communicating with it.

I know next to nothing about linux so i don't know how to do any of those things... and google isn't really helpful either sady...
i tried multiple cables, and currently i'm used the same cable i use for my TL866 II plus Programmer, so i know it's not the cable.
plus i sadly don't have an oscilloscope. i only got a simple logic probe (which is enough to tell that there is activity on both the D+ and D- bus)
the USBView program from FTDI shows strange stuff.
here is what my keyboard looks like in it:

and here what the FT240X looks like:

cjs wrote:

Obviously all of this is going to require some knowledge about how USB works. I have seen a great set of pages on this that could get someone at your level up to speed in no time flat, but I can't find the darn things now. But this article is short and might be fairly useful, and it also is probably worth at least scanning through the info on Wikipedia. I'll try to find better resources as we go along.

damn, the entire point of getting the chip was to avoid having to learn about the USB protocol.

[Dr Jefyll]

Proxy wrote:

i tried multiple cables, and currently i'm used the same cable i use for my TL866 II plus Programmer, so i know it's not the cable.

I would consider trying a different computer in case there's a defect on its USB port or something associated.

That may seem impossible, given that your TL866 II (presumably) works using that port. But it's possible for a USB port to be semi-defective -- I have witnessed this. I have a laptop with two USB ports. One of the ports isn't right -- it communicates properly with some devices but not others. It caused me some head scratching at first!

-- Jeff