STM32-based Arduino-compatible dev boards, round 2 (SushiBits M193v2) - Page 1
Forum section: electronics / projects

author: technix
author_rank: Super Contributor
timestamp: March 01, 2017, 08:59:47 am
content: Remember in one of the Mailbag episodes Dave have showed off my STM32-based, Arduino-compatible, low power capable dev boards, with a side comment on the name SushiBits? The second revision of the board is arriving, and I am thinking about expanding the options, hopefully without too much feature creep.Features with updates being highlighted:* MCU in LQFP-48 package, 3.3V supply voltage with some 5V tolerant I/O pins.* MCU options:STM32F072CBT6 (Cortex-M0 @48MHz,)STM32L152CCT6 (Cortex-M3 ULP @32MHz,) STM32F103CBT6 (Cortex-M3 @72MHz,)STM32F303CCT6 & STM32F373CCT6 (both Cortex-M4F @72MHz)* All I/O pins of the MCU broken out somewhere in the system, including GPIO, ADC, SPI, JTAG and USB pins.The only pin not attached directly to some connector is PC13 which is used to switch the USB pull-up resistor.* Arduino Uno form factor* Dual-layer board, single-side load only.* 32768Hz watch crystal with battery holder for RTC operation* Switch-mode buck regulators for 5V and 3.3V rails for ULP operation: TPS562200 for Vin to 5V, LM3671-3.3 for 5V to 3.3V.* Built-in USB to Serial adapter:WCH CH340B (it was CH340G on the previous version. CH340B allows for custom branding, serial numbers and custom VID/PID)* Two LEDs: Power andD13 (was D14 on the previous version)* Two physical buttons: RESET and WAKE.* USB is now wired properly, fast USB setup no longer required.* Vin range: 4-17V.Features for the next revision:* SMT crystals* Onboard USB UART + JTAG flash and debug unit based on STM32F103RBU6 (QFN-32 package) with individual power region. JTAG based on CMSIS-DAP.* Compatibility with STM32F2 and STM32F4 parts* Improved analog interface* A connected version based on STM32F107 and onboard Ethernet interface, with 802.3af PoE and IPv4/IPv6 dual stack support.

author: mikerj
author_rank: Super Contributor
timestamp: March 01, 2017, 03:43:11 pm
content: Sounds good, but could you squeeze a micro-SD connector onto your list? With the battery backed RTC it would make it more attractive for datalogging applications.

author: splin
author_rank: Frequent Contributor
timestamp: March 01, 2017, 05:02:14 pm
content: Make Vref accessible, preferably with some RC or LC filtering like on the STM32F407 discovery board - except they then hard wire it to Vcc so you have to mod it to provide you own reference.Solder bridges would be OK so the default would be to drive Vref from Vcc.

author: DBecker
author_rank: Frequent Contributor
timestamp: March 01, 2017, 08:02:04 pm
content: Quote from: splin on March 01, 2017, 05:02:14 pmIs there Vref on the 48 pin packages? I thought that it was only on the 100 pin and larger packages?Or do you mean AVCC? The STM32 ADC is notoriously noisy. Using a separately-regulated AVCC can improve the accuracy if you can't quiesce the peripherals when doing a conversion.

author: splin
author_rank: Frequent Contributor
timestamp: March 01, 2017, 09:53:34 pm
content: Quote from: DBecker on March 01, 2017, 08:02:04 pmThe STM32F373 has external reference inputs, VREFSD+ and VREFSD- for the 16 bit sigma delta ADC available on all size packages. These should not be hardwired to VDD and VSS, but options provided, probably as the default to connect them to VDDA and VSS.You're right though - I'd forgotten that the Vref input for the standard ADCs, DACs etc is only available on the larger devices (LQFP64 for the F373, TFBGA64 and LQFP100 for the F103 and LQFP100 for the F303), otherwise Vref and VDDA are connected internally.It would still be good to allow VDDA/Vref to be supplied externally, if required, by not hardwiring it to VDD, even if only by providing solder bridges. The user may wish to do this to ensure VDDA is clean to reduce noise in the analog peripherals and/or to provide an external reference that is better than the internal one. It would then be up to the user to ensure that VDDA/Vref >= VDD.Some filtering for VDDA and VREFSD would be good too.

author: technix
author_rank: Super Contributor
timestamp: March 01, 2017, 11:59:58 pm
content: Quote from: mikerj on March 01, 2017, 03:43:11 pmI don't have any spare I/O pins here. You can still use the existing SD card shields for Arduino for this. Or you can wait for the SushiBits STM32 Connectd Dev Board based on STM32F107, that does offer a SPI-based microSD card slot.

author: technix
author_rank: Super Contributor
timestamp: March 02, 2017, 12:05:06 am
content: Quote from: splin on March 01, 2017, 05:02:14 pmI didn't split the rails on this revision, as it is a small change from the first, just a quick fix on the power delivery and USB circuit. Next revision I will add a ferrite bead in the AVCC line so you just need to desolder to access AVCC or Vref.