very small STM32F405 board

1. If you are doing any flying things, the BetaFlight can be modified for your needs. For most cases, only minor changes are required. As the BetaFlight is based on the ST HAL library, there are a lot of related libraries and documentations available.

2. ST has been working with STM32duino and made the HAL libraries available for many STM32 Nucleo and Disco boards. As such, they can be used with Arduino IDE.

3. STM32duino has its own F4 support. The main target has been F407.

Related to this F405 board, I can observe that it is quite expensive compared to the classic style of boards. On the higher side, it has a limited performance compared to F745 board used in AnyFC-F7. With $30 you can get more connectivity, higher performance, and built-in IMU and still use the same BetaFlight library as used with F405. Many of these advantages are the fruits from the OpenPilot project done during the past years.

It is also quite expensive.

So IMHO only if use if you need a small powerful board but don’t need many GPIOs

one of those tiny F407VE boards i got are these
http://www.stm32duino.com/viewtopic.php … =10#p26277
http://www.stm32duino.com/viewtopic.php … =40#p27327
at about 2x the breadth of BP/MM 4cmx5cm it qualifies as a ‘tiny’ board with all the pins broken out and has an on board uSD card slot + on board crystals

then there are some other worthy competitors that are discussed in the thread
among them this board from olimex is pretty compact and decently priced
https://www.olimex.com/Products/ARM/ST/STM32-H405/

and you may also want to take a look at those micropython f405 boards which are true challengers in the ‘tiny’ arena who makes tiny f405 boards with as many pins broken out as is possible. micropython also throws in a 3 axis accelerometer MMA7660 on board and an ultra compact uSD card slot on a really tiny form factor
https://store.micropython.org/store/

It’s really small (50x40mm) but includes an i2c eeprom, and sdcard slot, and all MCU pins broken out.
I have still not used it, but plan to use it for my marlin tests.

[victor_pv – Thu Jul 27, 2017 3:58 pm] –
Just for reference, I recently bought one of these:
I have still not used it, but plan to use it for my marlin tests.

What is the tiny voltage reg there on the board?

http://www.stm32duino.com/viewtopic.php … 390#p31985

That regulator may work up to 200-250mA with 3.6-3.8V input.
For example:
P = (3.8V -3.3V ) * 0.25A = 125mW, the chip temp at ambient temp will be:

T = 0.125W * 250degC/W + 25degC = 31.25degC + 25degC = 56degC (hmm, you will burn your finger)

The problem of the chip used is its package – the thermal resistance (250degC/W) is so high, that that chip
catches fire. The larger 1117 reg package on other boards gets something like 60degC/W so the chip would be 33degC (with those 125mW) at ambient temp.

but i’d guess f4 being more power hungry vs f103, i’m not sure if we could or if it make sense to swap the on board LDO for a ams1117 or lm1117 when running off 5v

in addition i’m not sure if there is after all a feasible way to cool a sot23 ldo with a heatsink etc

[Pito – Thu Jul 27, 2017 10:30 pm] –

The problem of the chip used is its package – the thermal resistance (250degC/W) is so high, that that chip
catches fire. The larger 1117 reg package on other boards gets something like 60degC/W so the chip would be 33degC (with those 125mW) at ambient temp.

Thanks for the warning, I’ll feed it with 3.3V from another regulator.

Voltage Regulators Imax and Temp.JPG

Voltage Regulators Imax and Temp.JPG (101.22 KiB) Viewed 616 times

Voltage Regulators Imax and Temp 36.JPG

Voltage Regulators Imax and Temp 36.JPG (51.4 KiB) Viewed 611 times

R = x / ( A * k )

where:
R is the absolute thermal resistance (across the length of the material) (K/W)
x is the length of the material (measured on a path parallel to the heat flow) (m)
k is the thermal conductivity of the material (W/(K·m))
A is the cross-sectional area (perpendicular to the path of heat flow) (m2)

this would seem to imply that the rather high thermal resistance is partly due to the small size, hence small A, assuming that there isn’t any way to influence x and k.

this may somehow mean that if there is some ways to ‘heatsink’ that sot23 LDO, we may literally reduce the thermal resistance (and possibly significantly), this could for instance be possible by using some heatsink thermal compounds, but it would also mean attaching a heatsink so that all that heat is conducted away and dissipated over a (much) larger area.

the obvious problem is that it’d seem quite difficult to heatsink that sot23 LDO, as it would seem otherwise the LDO may possibly be able to handle higher currents than specs suggests. but on top of thermal problems, the MOSFET transistors used in the LDO may have actual electrical limits e.g. the minimum on resistance at the current voltages, that’d probably mean that beyond 300mA, the voltage dropout would be limited by the MOSFET on resistance and loses its ability to supply the desired voltages e.g.< 3.3v

Up to 17V input, 3A output, 2MHz, 90% eff at 1A, with integrated inductor, 3.0×2.8mm package.
Maybe it could be a good replacement..

[ag123 – Fri Jul 28, 2017 4:40 pm] –
this may somehow mean that if there is some ways to ‘heatsink’ that sot23 LDO, we may literally reduce the thermal resistance (and possibly significantly), this could for instance be possible by using some heatsink thermal compounds, but it would also mean attaching a heatsink so that all that heat is conducted away and dissipated over a (much) larger area.

increasing the pcb copper area for the LDO is not possible.
cringe if you wish, lift the tab insert copper plate and resolder both to original copper pad

otherwise lift the LDO and use 3 wires to another regulator with a heatsink appropriately mounted
srp