XPortHub Rev 1.2 Annotated


  1. CAN
  2. CAN
  3. RS485
  4. RS485
  5. Terminal switch for CAN & RS485
  6. USB
  7. Micro SD Card
  8. SPI Flash
  9. RTC Battery
  10. Power connector
  11. I2C
  12. SPI
  13. TTL UART
  14. RS232
  15. RS232
  16. Raspberry PI Connector
  17. STM32F405RG
  18. SWD Connector

Changes from Rev 1.0

1 Corrected wrong SPI Flash package
2 Added resistors to SPI 1 to support Half-Duplex SPI
3 Replaced supercap with CR1220 battery holder.
4 Several PCB changes to optimize ground plane.
5 Changed DIP switch order to match port order on board.
6 Changed to new SWD header.

Sensor IO Hat Annotated

This is a 3D of my Sensor IO Hat Rev 1.0 that allow interfacing to 8 x Analogue/Digital sensors, 3 x I2C and 3 x SPI. STM32F405 have 16 x 12 bit ADC channels and each AD port have 2 IO pins that can be used . The Sensor IO Hat is about connecting to sensors as it have no sensors of it’s own. The only extras here is the Flash and RTC. 

  1. Standard CAN port.
  2. 8 x AD port consisting of 2 x Analogue/Digital Input/Output each allowing up to 16 analogue or digital sensors in total.
  3. I2C port
  4. Battery adaptor for RTC.
  5. Leds
  6. USB port
  7. 2 x I2C ports
  8. 3 x SPI ports with separate CS each.
  9. SPI Flash
  10. New SWD Connector.
  11. STM32F405RG
  12. RTC Oscillator
  13. Raspberry PI connector.
  14. TVS diodes giving a minimum of pulse protection to IO lines.

The block diagrams of these Hat’s are almost identical with exception of IO features and that is deliberately to make SW development easier.

The “New” SWD is based on 2×5 pin 1.27 pitch header and I removed the 5V and UART from the previous version. I tried a 6 pin using JST Micro but found them hard to mount on/off + I had some trouble with the added signal length. This design show here have however worked well and the 2×5 pins are easy to get. Even more important is that using a special male adapter I can program the board without soldering the connector at all.

All SWD connectors will be changed to this format and face in a direction making it easy to plug them in even if a board is in the middle of a stack. For now I still operate without a bootloader, but later I will only program the bootloader and use a USB + SPI to program Boards.

Linux Ethernet Switch/Router Hat

The most obvious Hat to use HLK-7688A on is a Ethernet Switch or Router with SPI backbone support. I have ordered a dev unit so I can test out this possibility. The Ethernet switch part is very straight forward, I also see a very decent SPI, but I need to dig a bit more into that before I decide on wherever this is a path forward or not. An alternative is to use the two UART’s to a classic STM32F405 if that does not work out or even use a STM32F407 and connect on the 5th Ethernet, but now it gets more complicated. I am also a bit concerned about taking on a work-load that includes a Linux distribution. I seriously hope this can be limited to making apps and a easySPI driver.

MT77688AN have 2 SPI’s, of which one do not have half-duplex and I suspect that the other already is connected to a Serial Flash, so using SPI for easySPI might not be straight forward or possible at all. But, that is something I need to learn more about.

One of the dev kits for HLK-7688 is a switch/router, so it is quite easy to just get the SPI lines and see if I can do what I want. I will obviously have a size issue on the Hat, but I can get a minimum of 3 RJ45’s + I can get more if I use 5 pin Micro JST connectors only – lets see.

The Age of Linux

Linux started seeing a serious increased usage in embedded projects with raspberry PI due to it’s availability and low cost. And the last years have provided a large number of low cost embedded Linux solutions. They are getting smaller, more powerfully and decreasing in cost making them very attractive in projects. Raspberry PI might still be the king, but it is far from alone these days. Having been involved in a few projects using Linux I must admit that it is very attractive to have a Linux Core as soon as you have Ethernet or Wifi involved.

The module above measure 18x33mm and run Linux. It is no comparison for the larger Raspberry PI or BeagleBone boards, but it cost ca 9.- USD , have a small size and some very interesting features.

This shows a block diagram. The module uses the HLK-7688A SoC and add 128MB Ram and 32Mb Flash in the module. This is supported by Linux/OpenWRT and one of the 19.- USD dev kits is a 5 port LAN/WAN router.

  • MCU is MT7688AN ticking at 580Mhz w/128Mb Ram and 32Mb Flash.
  • Size 18×32.8z2.8 mm.
  • Cost ca 9.- USD
  • Wifi with ITX antenna as well as supported on the pins.
  • I2S
  • I2C
  • SPI
  • USB
  • SD-Card
  • JTAG
  • 5 x Leds (GPIO)
  • 2 x UART
  • 5 port Ethernet 10/100Mbps
  • + more

The module above is Beaglebone TI AM3352 costing 19.- USD. A little to large to fit on a Hat size, but this one is a serious competition to Raspberry PI. It also have several bigger brothers. The main attraction with the Siera is that it also have PRU’s – co-processors capable of very fast IO.

Moving on I was initially planning a Ethernet module w/ESP32, but are seriously thinking about making a 3 port Router/Hat w/HLK-7688A. I just need to convince myself that the toolchain is available and easy to deal with. I am actually a bit spooked as this involves dealing with a Linux distribution, but lets see.

STCubeIDE Review 2

I have struggled a little to find an IDE I was OK with, but finally settled with STCubeIDE or Eclipse as it actually is. This is IMO one of the smarter moves that ST have done to support their MCU’s. The editor is “ok”, it compiles, download allow you to debug multiple targets + I get a more familiar feeling with the dark theme. It is load of eclipse add-on’s I have not tested, but I downloaded PyDev and can develope both Python 3.7 and 2.7 in parallell With full debugger support. The later is developed by a single developer who deserve credits for hes work, and it demonstrate one good argument to use Eclipse as base. As for Python the less I have to use that Language the better, but PyDev actually took most of the pain away.

It is still a few tricks using STCubeIDE and set it up, but it is worth it. One of them is how to add existing files to a project, but True Studio (as this actually was) is a big improvement over bare eclipse.

I am also using Code::Blocks on a different project yet since colleges have selected that and that works ok as well. But, despite my disliking of Java – I actually like STCubeIDE. The best is that I don’t need to know that this is written in Java 🙂 – I can actually be an user and focus on my own tasks and productivity.

This has actually been a showstopper for SW modules on my STM32 based components and I have finally started getting my act together and make a serious move on SW. What I will be working on for some time is the Abstraction Layer (AL). I am ditching the STCubeMX and autogeneration part. I autogenerated 1 project and use it to cut & paste as I set up the proper C++ project. Currently I am working on the abstraction layer to hide the C drivers and middleware packages completely behind a proper C++ layer.

One of the features I really like is the visual memory map showing you what is using what memory. It is still a lot of extra tools in STCubeIDE that I have left to discover, but that will come with experience.

I also tried setting up Visual Studio Code, but aborted simply because it is more an advanced editor than a proper IDE.

DSO150 Oscilloscope Annotated

DSO150 is very easy to use and operate like a multi-meter, and this caught my attention because the other Oscilloscopes I havve needs to be set up. DSO150 is basically only to switch on and use like a Multi-meter – you instantly see the signal and it was surprisingly easy to operate the HMI. I added a 9V battery to make it mobile and to avoid isolate the instrument. And all for a cost of ca 20.- USD.

Holding the OK button switched numbers on/off. V/Div adjust Y-scale gain and offset. Sec/Div adjust X-Scale gain/offset. Trigger select between Auto, Normal and Single shot as well as select between triggering on rising/falling edge. OK also hold the sognal so it freezes on screen. It takes a little practice to play and operate it, but once you get it into your fingers it actually is very functional for what it is.

It’s loads of things to complain about on DSO150 if you compare it to a professional Oscilloscope, but DSO150 cost 20.- USD and come in a form of a multi-meter. I actually only have one suggestion – add a battery holder and add USB. My point is that I do have Professional Oscilloscopes and this actually fills a gap between the multi-meter and those Scopes. I already had a small, hand-held Scope, but the HMI – button/knob solution on DSO150 is so more functional.

And yes – please chose a better MCU and increase bandwidth, but here is the catch – if someone does that it will not cost 20.- USD anymore. I need to glue a 9V battery holder on the back, but other than that this is perfect for those cases where I just need a simple scope solution to replace the volt meter.

The STM32F103C8 is a bit limited, but I can easily replace that with STM32F103CB or even STM32F303CC to get more Flash, SRAM and DSP power. I have not downloaded and played with the source code yet, but this is another attraction – an instrument I actually can program myself .

DSO150 – 20$ Oscilloscope

This Oscilloscope took me by surprise. I ordered it mostly for fun, but it turns out to be very functional and easy to operate Scope in a multi-meter format. 200Khz actually cover a lot of the activities I do and by attaching a battery you get a very handy, single channel Oscilloscope in a handy form factor.

The best of it is that schematics is open Source, firmware is open Source and it’s a hidden UART inside the Scope opening some possibilities. The quality is not the best, but a lot of times I just need to see what happens on a channel and this does that job perfectly.

The picture above show the PCB with 2 x GPIO ports, SWD port and an UART port. The MCU used is STM32F103C8. You can also see the EEPROM programmable via I2C as well as the extra Power Connector at bottom left. Below the MCU you can also see 2 test-Points that accidentally is the USB port. The Connector at top right is for the analogue Board that click on to this. All in all a cute little design. The DSO150 that I got is obviously a cheap clone. What I have done is to attach a 9V battery so it becomes like a portable multimeter.

Rock PI 4 b

I accidentally came across “Rock PI 4 b” and first believed it was about Raspberry PI 4 as I realized this is a board based on Rockchip RK3399. It is very similar to Raspberry PI 4, but contain some very interesting differences. Of most interest for me is that the form factor and GPIO pin layout is compatible, meaning I can use my Hat’s on this directly. Lets outline some of the differences.


Rock PI 4 b Rasberry PI 4 b
CPU RK3399 BCM2711
Cores 6 Cores

2 x A72 @ 1.8Ghz

4 x A53 @ 1.4Ghz

4 Cores

4 x A72 @1.5 Ghz


GPU Mali T860;P4 VideoCore VI 3D

500Mhz 32 bit

RAM 2,4Gb 1,2,4 or 4Gb
Micro-SD Yes (128GB) Yes
USB 2 x USB3

2 x USB2

2 x USB3

2 x USB2

USB OTG Switch Yes No
RTC Yes No
eMMC Socket Yes up to 128GB No
PCIE M.2 socket Yes Support up to 2TB SSD No
Ethernet Gigabit Gigabit
Wifi Yes Yes
Bluetooth Yes Yes
Sound ? 4-pole stereo
Camera Port Yes Yes
Display Port Yes Yes
HDMI 1 x Standard HDMI 2 x micro-HDMI

2 x 4Kp60

GPIO 40 pin RPI standard 40 pin RPI standard
PoE Possible Possible
Price 67$  (4Gb) 55$ (4Gb)

The eMMC interest me as it allows me to boot from Flash making this an interesting option for more commercial solutions. Other than that I must admit that 2 x HDMI etc only is of interest if you replace your desktop PC.


Raspberry Pi 4

  • Quad core 64 bit Cortex A72 1.5 Ghz
  • 2 x 4K HDMI ports
  • USB 3
  • Gigabit Ethernet
  • Up to 4GB RAM
  • and more

Priced at 35$ for 1GB and 55$ for 4Gb this starts to look like a serious challenge for more classic desktop computers. I tried to buy one, but getting the “sold-out” from all shops. Read more at  https://www.raspberrypi.org/blog/raspberry-pi-4-on-sale-now-from-35/

Well done Raspberry PI