F405 & F411 versions of the BluePill

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Mon Jan 15, 2018 9:59 pm

The BluePill F4 board top side is pretty crowded, so there is not much space left there. But on the bottom side, you can see that there is still space left between the row of PC1-PC7 pads and the SWD header:

Image

As traces and pads on a PCB cost nothing except for the time you spend laying them out, it may be a good opportunity to etch some useful circuit that may be commonly used by developers. This is why I started by adding the LiPo charger circuit above as a nice option 8-)

I checked existing STM32 designs for more ideas: ST own Nucleo and Discovery boards, 3rd-party boards like Olimex or Itead, language-oriented Espruino and pyboard boards, and also some more specific boards for flight controllers or autopilots like Pixracer and Paparazzi.

In no particular order, here is a list of possible integration candidate circuits:
  • Audio (I2S codec or analog interface to ADC/DAC): probably too big to fit and not of general interest
  • 2.4GHz RF module: too big
  • LCD/OLED screen: like the NodeMCU+OLED combo
  • Micro-joystick (on bottom face?)
  • Reset controller chip
  • Ethernet: too big
  • USB TVS: would be difficult to add as an option, and not required on a bare dev board unless it is integrated into a product
  • RS232 buffer
  • Bluetooth module: too big
  • Coin-cell battery or "Gold Cap" for RTC
  • FRAM/Flash SPI chip (SOIC8): tried to fit a footprint as an alternative to the SD Card connector, but this results in turning the nice (small) GND plane below the main LDO to pieces => not good
  • MOSFET for power output (buzzer, relay, etc.): how to make it optional?
  • Battery voltage resistor divider
  • CAN transceiver
  • 3, 6 or 9-axis IMU (Inertial Measurement Unit), e.g. accelerometer, gyroscope, magnetometer, pressure sensor (altitude): problem is most of them are soldering iron-unfriendly QFN packages :( These are used of course in all flight controller or autopilot boards, but also on more general-purpose boards like the ST boards (they sell MEMs...) and pyboard, for example...
  • "FrSky Inverter", e.g. a dual XOR gate to invert the level of UART signals as used by this common R/C protocol
  • ...
Please let me know what do you think of this, or if you have even more circuits to propose!

victor_pv
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Re: F405 & F411 versions of the BluePill

Post by victor_pv » Tue Jan 16, 2018 3:27 am

i2c eeprom/fram and pull up resistors foot print?
May be a good option if routing one of the i2c ports there is easy, since it's just 2 data lines and power.
Not sure how frequently other people use them, I have used them a couple of times to avoid wearing out the flash, but the board already has sdcard for stg too...

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Tue Jan 16, 2018 7:06 am

Yeah, the problem is not much SPI here as there are PB2-PB15 for SPI MOSI/MISO/CLK/CS signals in this area, but the SOIP8 footprint itself, which totally destroys the GND plane under the SD Card connector :?

I2C FRAM/Flash are 4x to 50x slower than their SPI counterparts, but they may still be useful, you are right. They will then be easier to place in the large empty area below the buttons, and I2C is indeed requiring only 2 signal wires which are easy to find. Maybe a combination of alternative I2C footprints could be nice to have? Like the FRAM/Flash, some I2C sensors, 0.91" OLED screen, etc?

racemaniac
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Re: F405 & F411 versions of the BluePill

Post by racemaniac » Tue Jan 16, 2018 7:17 am

i'm sticking to my opinion of starting out with the current iteration, and having a look at how it performs ^^

i think we're now at a point where it is interesting to order a few boards and build a few prototypes? :)

aster
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Re: F405 & F411 versions of the BluePill

Post by aster » Tue Jan 16, 2018 12:25 pm

👏👏👏👏 very nice!

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Tue Jan 16, 2018 1:00 pm

The real deadline is CNY 2018 (Chinese New Year 2018), which this year is happening on February 16th, so you can expect factories to be closed from 11th to 24th at least, but plan for an additional week after that as some workers may not come back to work :o

This means that we have around 2 weeks to finish the design, or we will only get the boards on mid-March.

I have most of the components available to make a few boards.

If nobody spots more problems in the current version, then the only thing left is to duplicate the PCB to add the teardrops, at least for a better drill to pad tolerance, mechanical and thermal stress. It looks like the board dimensions are too small for www.allpcb.com to do V-cuts, but they accept tab routing and they propose to do it themselves for free, resulting in a total cost including 24h lead time and TNT shipping to France (3-5 days) for 40 pieces @ $20 (60 pieces are only @ $23 !?!). Unfortunately at this price, the boards will be green, not blue, this adds $8 more :)

We do not take many risks by adding footprints on the bottom side for some I2C or other simple devices like voltage divider, MOSFET, etc. But we have to decide what we want asap, as everything will not fit.

michael_l
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Re: F405 & F411 versions of the BluePill

Post by michael_l » Tue Jan 16, 2018 1:16 pm

Just wanted to say this new F4xx version of BluePill looks really awesome! I have been using BP for a while now and usually the problem has been that I run out of RAM and Flash and I'm using FreeRTOS.

Having microSD card is already a killer feature!

As for extra circuit I vote for 1) Extra (F)RAM 2) CAN transceiver 3) Battery resistor driver

Ollie
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Re: F405 & F411 versions of the BluePill

Post by Ollie » Tue Jan 16, 2018 7:24 pm

Once we have the new F4 blue pills from manufacturing, what is the process to purchase them? I would like to buy one.
- when is it estimated to be available?
- what is the estimated total price for US customers?

Cheers, Ollie

ChrisMicro
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Re: F405 & F411 versions of the BluePill

Post by ChrisMicro » Tue Jan 16, 2018 7:26 pm

Just one remark to the "SD-card exchange problem":
To exchange the SD-card on the bottom side when the F4BP is soldered is probably impossible.
Therefore one solution would be to place the SC-card connector on top btw to flip the whole board as it is before soldering onto a PCB. But then the buttons and leds are also on the bottom and can not be accessed.
So a solution would be to place the SD-card, buttons and leds on top and the rest of the components on bottom.

So, why should someone want to exchange the SD-card?
There are many reasons:
1. The F4 is capable to play MP3 files
2. Someone makes a data logger and wants to transfer the collected 16GB of data by exchanging the SD-card
3. SD-cards are not famous for the life span

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mrburnette
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Re: F405 & F411 versions of the BluePill

Post by mrburnette » Tue Jan 16, 2018 7:41 pm

ChrisMicro wrote:
Tue Jan 16, 2018 7:26 pm
Just one remark to the "SD-card exchange problem":
To exchange the SD-card on the bottom side when the F4BP is soldered is probably impossible.
<...>
On the surface, your argument is sound. The reality is that I have been playing around with the rPi_Zero-W since they were first available, and it is very, very rare to have to remove the SD card.
Cards today are all wear-leveled and are very tough. A little bit of S/W to manage the filesystem should go a long way to dealing with not needing to remove the card... that is, if using for logging, have an option that spools the file to the serial port of the PC (or USB) and a dialog requesting "Delete?" at the end of the spooling will do necessary housecleaning.
If the board is mounted upside down, small holes in the hosting board or enclosure can be utilized for the buttons. Slap a label over the holes if you want it dust free.

Just thinking out loud.

Ray

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