Category: research

research projects

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rotabench ECO Rev 01

… a lightweight Ethernet to RS485 and CAN Converter

With the end of support for Windows 10 there came a difficult decision for me: upgrade all test bench + device control PCs to Windows 11, or leave them on Windows 10? I decided against the upgrade. It would have meant to spend money and lots of work/time to re-establish the status-quo ante, just to get the prior functionality back. Instead I followed the advice “never change a running system”, created a 2nd network without internet access for lab-use only and migrated most of the rarely used control machines into virtual machines.

rotabench ECO Rev 01
rotabench ECO Rev 01

While Hyper-V on Windows 11 is a convenient approach, it has a major drawback: no USB pass-through. The official statement from MS, why there is no USB pass-through, is due to security reasons. Well, yea, sure …

This means I can not use my USB-devices, like my NI USB-RS485 or NI USB-CAN adapters on a Hyper-V virtual machine, when my software needs eg. RS485 communication or a CAN Bus. As my software was written for Windows, I had to stick to it, and I needed a simple approach to give my software its hardware capabilities back. Porting all this software to Linux would cost me years, so that’s not an option. So I built this:

rotabench ECO R01a KiCAD screenshot
rotabench ECO R01a

An Ethernet & USB to RS485 Half Duplex and RS485 Full Duplex Converter, with 2 CAN Ports, based on an STM32H7 MCU. And as I could, I made the device driver-less. The TCP-IP Protocol is the “driver”. And because there were still pins free on the MCU after all the mandatory elements were placed, I gave it 8 MB QSPI-SRAM – just in case.

Full Feature List:

– RS485 Half Duplex Port
– RS485 Full Duplex Port
– 2 CAN Ports – CAN-FD (5 Mbit/s) capable but not yet implemented in the Firmware
– 10/100 Mbit Ethernet
– USB for configuration
– 8 MB QSPI SRAM, 16 MB Flash Memory, 8 kb EEPROM
– STM32H723 MCU @ 550 MHz

On the software side, I simply have to add the communication library to my software and re-route the communication over Ethernet, instead of using the drivers like NI-Serial. This also means the device is implicitly cross-platform, as the protocol is the same on every platform.

no AI was used in the engineering process. Only human brain cells were tortured.
no AI was used in the engineering process.

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Signal Conditioning PCB for LEM CT-200 Current Transducers

Hot on the bench: Signal Conditioning PCB for LEM CT-200 current sensors.

LEM CT-200 Signal Conditioning PCB
LEM CT-200 Signal Conditioning PCB

I just finished soldering the first samples of my signal conditioning PCB for LEM CT-200 current transducers. These devices converts the current output of up to 4 current CT-200 transducers into a voltage. For high precision I use Vishay Z-Foil burden resistors with an accuracy of 0.02% and a very low temperature coefficient. With some reduction in accuracy also CT-100 or CT-60 sensors could be used.

Format: 160 x 100 mm, 4 channels with Vishay Z-Foil 5 Ohm 0,02% burden resistors. Passive cooling. Power Supply: 2 x 18 Volt DC. The 5 Volt Rail for the Sensor Status output is generated by a DC-DC converter on the PCB.

Each Channel has a +-10 Volt (DC) Output and a 1 Volt RMS output on SMA connectors. The 1 Volt RMS outputs are intended to be used with my new-old Norma D6100, the 10 Volt Outputs go to a compact RIO.