Can I use UbiSwitch without transformers?

BotBlox Hardware
1

– Copied from customer email –

I am planning to use BotBlox BB-UBS-B-1 without switchboard base BB-UD1-B-1.

Can I connect the equipment’s directly to BB-UBS-B-1 ports (10/100/1000 BASE T)?

Does it have transformers?

2

The 10/100/1000BASE-T ports on UbiSwitch are voltage mode, which means that, in general, you can connect them to other devices without transformers. Instead you would need to put series capacitors (0.1uF, X7R, 0402, 50V) on each line. This is called capacitive (sometimes also called transformerless ethernet) coupling, and it prevents differences in ground potentials between UbiSwitch and the connected devices.

Bear in mind that transformerless ethernet does not work in all cases. If you are connecting to devices that are far away (more than 10 meters), or the devices you are connecting to are running from a different ground, you need the transformers. For example

  1. Inside a drone, where all devices are close by, there is a single ground, and the connected devices will not change, transformerless ethernet will work.

  2. On industrial equipment, where some devices may be far away, on a different ground, and there is potential for customers to connect different things during operation, transformerless ethernet will probably not work.

Can you let me know what the ports will be connected to, and a bit more about your system, and I can suggest whether transformerless ethernet will work for you.

We also offer a free design review service for customers integrating our products, along with a free consultation call to discuss the technical details.

3

– Copied from customer email –

Thanks for your prompt response.

The Ethernet switch will be present inside our device along with the few small motor drives and camera. All cameras and motor drives are powered through the control box power supply. We are not going to use PoE.

We are going to use Port 1 to 8 (10M,100M,1Gb ports only).

So far, we don’t have isolated grounds.

Our device has cameras and drives inside, but a large sword probe. The sword probe is 40ft long and has a camera to the tip of the sword. This camera is connected to the ethernet switch.

The problem with UbiSwitch Baseboard SS-UD1-B_1 is we don’t have enough space to install inside the cart as the cart is so small. We only have 5” hole to get into the steam generator.

4

From the sounds of things, everything in your system will be on the same ground, and the lengths are not so long. It also sounds like you will not change the devices connected to the ethernet switch during operation. This is all good news and indicates transformerless ethernet will work fine.

The final thing to check is whether the connected devices contain transformers or not. Ideally, all connected devices do contain transformers. If not, then we have to consider if there is interaction between the ethernet chip and the connected devices ethernet transceiver. You could open up all the devices, check the part number of the chip, and look at the datasheet, but there is an easier way.

We already sell a transformerless ethernet system, GigaBlox Nano + PicoConn. You could purchase a pair (~$100) and connect your devices to this. If it works, then it’s highly likely it will work with UbiSwitch in a transformerless configuration.

Finally, you mentioned motor drivers inside your cart. As I’m sure you’re aware, motor drivers tend to emit a lot of EMI, which can interfere with the ethernet signals, so you’ll need to ensure the boards are decently spaced apart, with minimal crossover of wiring. Most of our boards are heavily used in drones, so use with motor drivers is not uncommon, but it’s just something to bear in mind.

5

– Copied from customer email –

Thanks for the explanation, I have another question.

The STM32F4 has RMII mode.

Can I connect STM32F4 ethernet pins to Port 10 of Ubiswitch?

Please confirm the following:

  • I will need MDC_CPU, pin 33 to connect to MCU’s MDC pin
  • MDIO_CPU pin 35 to MCU’s MDIO pin
  • SE_SCLK, pin 4 to MCU’s
6

UbiSwitch has three ports that you can connect to an external CPU, port 0, 9 and 10. Only the SerDes pins of these three ports are only broken out on the stacking headers. This means they can only connect via 1000BASE-X, SGMII, 2500BASE-X, 5GBASE-R, 10GBASE-R or USXGMII. That means you can’t connect to port 0 using an MII port on UbiSwitch. In other words, an MCU that only has RMII cannot exist on the “data plane” of UbiSwitch (aka, it can’t receive ethernet packets).

However, in your pinout, you mention MDC and MDIO. These are configuration pins for the switch, and you can connect these to your MCU. This gives you access to the “management plane” of UbiSwitch, which you can use for configuring network features.

UbiSwitch already has an MCU connected to these pins which is already used for management features however.

I guess my question is “what are you trying to achieve?” If you just need basic switch management then you can do that over the MDIO/MDC lines with your MCU (but then, why not just use the microcontroller onboard UbiSwitch). If you need more capable network features where the MCU is in the “data plane” then you need a MCU that has more than just an RMII port.