"LC Technology" STM32F103C8T6

Generic boards that are not Maple or Maple mini clones, and don't contain the additional USB reset hardware
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ddrown
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"LC Technology" STM32F103C8T6

Post by ddrown » Tue Mar 01, 2016 5:29 am

I have a generic board labeled "LC Technology" on the bottom and its USB doesn't work. I decided to take a closer look at it on the scope. PA11 (USB D-) was at 5V and PA12 (USB D+) was at 3V, with just a steady voltage. Comparing to my other board, PA11 was at 0V and PA12 was at 3V and roughly every 1ms there's some data. I assume that's the USB Start of Frame (SOF). So I'm pretty sure D- shouldn't be pinned to 5V.

Pictures:
LC-Tech-Top.jpg
LC-Tech-Top.jpg (140.01 KiB) Viewed 2412 times
USB part of the schematic I found:
LC-Tech-Circuit.PNG
LC-Tech-Circuit.PNG (6.81 KiB) Viewed 2412 times
The schematic looks fine. Powering the board through the 5V pin and no USB plugged in, the USB D- line is still pulled to 5V. This makes even less sense as the STM32 can't be doing that. So I test resistance between USB D- and 5V and find it's 0ohms. :shock:

There's some residue in that area and there's something that might be a solder bridge between these two pins under the jack's cover where I can't see it very well. 5V is the right-most pin and D- is the pin just to the left of it.
usb-jack.jpg
usb-jack.jpg (118.02 KiB) Viewed 2412 times
So, that's something to look out for.

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zoomx
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Re: "LC Technology" STM32F103C8T6

Post by zoomx » Tue Mar 01, 2016 8:21 am

:shock:

Thanks for sharing this.

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ahull
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Re: "LC Technology" STM32F103C8T6

Post by ahull » Tue Mar 01, 2016 8:17 pm

Take care with that board, the quality can be pretty low if it is the board I am thinking of.

Search this forum for "ugly board". Also be aware that as shipped there is probably a zero ohm link between VCC and VBAT called R14.

This makes life very interesting if you add a button cell to power the RTC. The battery will explode. It is in other words a bad idea, unless you have a thing for exploding button cells. See here for details.

According to the STM documentation, this link should be omitted, or should be a small value capacitor (I can't remember which document mentions the capacitor, or its value). I removed the link, and the RTC worked fine on mine. In short, (pun intended), remove R14, it is a waste of time, and potentially dangerous.

Also check the jumper settings, I seem to recall, that they are connected in some way with the USB pins, but I can't remember exactly how, and I don't have the board to hand. One of them may be your mysterious short to +5V
- Andy Hull -

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RogerClark
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Re: "LC Technology" STM32F103C8T6

Post by RogerClark » Tue Mar 01, 2016 8:43 pm

There is some other design fault on that board.

You may find it does not boot up when not attached to a PC.

I cant get the bootloader working on that board.

I have no idea why the bootloader does not work. I thought it may be something to do with the oscillator not starting up cleanly, but I tested a few changes, but I could not get it to work.

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ddrown
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Re: "LC Technology" STM32F103C8T6

Post by ddrown » Wed Mar 02, 2016 4:10 am

ahull wrote:Take care with that board, the quality can be pretty low if it is the board I am thinking of.

Search this forum for "ugly board". Also be aware that as shipped there is probably a zero ohm link between VCC and VBAT called R14.

This makes life very interesting if you add a button cell to power the RTC. The battery will explode. It is in other words a bad idea, unless you have a thing for exploding button cells. See here for details.

According to the STM documentation, this link should be omitted, or should be a small value capacitor (I can't remember which document mentions the capacitor, or its value). I removed the link, and the RTC worked fine on mine. In short, (pun intended), remove R14, it is a waste of time, and potentially dangerous.

Also check the jumper settings, I seem to recall, that they are connected in some way with the USB pins, but I can't remember exactly how, and I don't have the board to hand. One of them may be your mysterious short to +5V
Hah! Yup, R14 is a 0 ohm between VBAT and VCC on mine too. Thanks for the heads up!

The jumper adds a 1.5k between USB D+ and 3.3V, you can see it in the schematic. That part looks ok to me.
RogerClark wrote:You may find it does not boot up when not attached to a PC.

I cant get the bootloader working on that board.

I have no idea why the bootloader does not work. I thought it may be something to do with the oscillator not starting up cleanly, but I tested a few changes, but I could not get it to work.
I didn't run into this at all. I was able to flash the stm32bootloader. I put an external LED on PC13 and powered the board by putting 5V on the 5V pin, and it does a fast blink on bootup.

I was also able to flash a simple blink loop with a stlink.

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RogerClark
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Re: "LC Technology" STM32F103C8T6

Post by RogerClark » Wed Mar 02, 2016 4:42 am

@ddrown

OK

I'm glad it works for you. But not for everyone (not me :-( )

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ahull
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Re: "LC Technology" STM32F103C8T6

Post by ahull » Wed Mar 02, 2016 11:08 am

RogerClark wrote:@ddrown

OK

I'm glad it works for you. But not for everyone (not me :-( )
Roger, mine also works reasonably well, considering the dodgy soldering, I suspect that the poor quality control and rough soldering may be the issue with the one you have.
- Andy Hull -

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mrburnette
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Re: "LC Technology" STM32F103C8T6

Post by mrburnette » Wed Mar 02, 2016 12:32 pm

ahull wrote:<...>
suspect that the poor quality control and rough soldering may be the issue with the one you have.
Or maybe those hand selected components are not up to a second life ...
ewaste[1].jpg
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Ray

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martinayotte
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Re: "LC Technology" STM32F103C8T6

Post by martinayotte » Wed Mar 02, 2016 2:38 pm

:lol:

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ahull
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Re: "LC Technology" STM32F103C8T6

Post by ahull » Wed Mar 02, 2016 3:59 pm

I'm all for recycling of parts, so long as the QA is there.

The average lifespan of a consumer gadget seems to vary in inverse proportion to Moore's law (perhaps we should call that Eroom's law, or ahulls law).

The more transistors we cram in, the shorter the lifespan of the product, so anything that extends the service life of gizmos is probably a good thing...

However having said all that, why does that idiot on the left of that big pile of crap cheap components shortly to appear in the Shenzhen electronic market (and shortly thereafter, no doubt on ebay) appear to be eating a PCB? :roll:
- Andy Hull -

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