In a recent blog post, I suggested to replace multiple display computers in a driver cabin by one computer in a silver box with multiple displays. I didn’t specify which connectors and cables to use between computer and displays. I found the answer at Electronica 2018 last week: High-Speed-Data or HSD connectors. You can use HSD connectors for LVDS (including Display Port), APIX, CAN, USB 2.0, USB 3.0, Ethernet and Firewire.
The Present: Low-Frequency Connectors like Deutsch
Connectors in driver cabins of heavy-duty vehicles like harvesters, trucks and construction machines must satisfy two requirements. First, connections must withstand heavy vibrations. Vibrations must not loosen connectors and make them fall out eventually. Second, connectors must have protection levels IP54 or IP55. They must be dust protected and must withstand splashing of water or water jets.
These two requirements make it clear why consumer HDMI or DP (display port) connectors won’t cut it. They also explain why Deutsch connectors are popular in heavy-duty vehicles. They sit very tightly in their sockets and the inevitable coffee or coke spill cannot harm them. However, Deutsch connectors are not suited for high-frequency signals, which are needed for data rates in the Gb/s range.
Today’s high-end displays in harvesters have a resolution of 1280×800 pixels with a color depth of 24 bits per pixel at a refresh rate of 60 Hz. The computer must send 1280 * 800 * 24 * 60 = 1,474,560,000 bits per second or roughly 1.5 Gb/s to the display. Deutsch connectors cannot handle such data rates, let alone the data rates for full HD and 4K displays (see the table Resolution and refresh frequency limits for the required data rates).
This simple calculation may reveal why current driver terminals only have internal displays. Inside an IP54 or IP55 enclosure, the SoC can be connected with the display using a standard LVDS cable. The LVDS cable is protected against the environment by the enclosure.
The Future: High-Frequency Connectors like HSD
At Electronica 2018, halls B2 and C2 were my home for the better part of a day. Connector manufacturers like TE Connectivity, ODU, Rosenberger, Harting and Amphenol showed their goods in these halls. I told them my story as outlined in the previous section and asked them for the best solution.
The sales person at the TE Connectivity booth suggested to have a closer look at HSD connectors. Trucks use HSD connections mainly to move data from cameras to displays. Car manufacturers like Volkswagen and Daimler, which also build trucks, drive the adoption in cars. Autonomous driving needs to move enormous amounts of sensor data to the central computer in the vehicle. Unfortunately, TE Connectivity didn’t have any HSD connectors on display. But at least, I knew what to look for.
I finally found HSD paradise at the Rosenberger booth. Rosenberger’s sales person gave me an instructive introduction into HSD connections and a connector kit (see Figure 1).
HSD connectors and cables have four conductors and wires, which are arranged in a star-quad topology with two differential signal pairs decoupled from each other. You can see the star-quad topology with plugs 5-9 in Figure 1. They work at frequencies of up to 6 GHz, which makes them ideally suited for data rates in the Gb/s range. HSD connections are used to transfer image data from computers to displays or from cameras to computers for processing.
Display port (DP) uses LVDS at the physical layer. HSD supports LVDS. Therefore, you can use an HSD connection to transfer the display contents between a computer and a touch display. One wire pair in the star-quad HSD connection is used to transfer the display contents from the computer to the display. The other wire pair is used as the back channel to transfer touch events from the display back to the computer.
So, you can connect the computer in the silver box with multiple touch displays via HSD connections (see Figure 2). HSD scales from HD displays to 4K displays.
Not Just for Display Data
You can use HSD connections for a lot more than transferring data between computers, displays and cameras. The two CAN connections in Figure 2 can be replaced by one HSD connection. As typical CAN data rates are between 256 Kb/s and 1 Mb/s, you can use unshielded HSDe connections. HSDe connections are cheaper than the normal HSD connections.
The 10 or 100 Mb/s LAN connections between the cameras and Switch 2 in Figure 2 can be replaced by 10 or 100 Mb/s HSD connections with power pins (see plug 5 in Figure 1). The cameras don’t need an injector with a separate power connection any more. You can also replace the LAN connection between Switch 2 and the Silver Box by an HSD connection. A single HSD connection is sufficient for data rates up to 100 Mb/s. For higher data rates of up to 1 Gb/s, you need a double HSD connection (see plug 8 in Figure 1).
Two BroadR-Reach connections with a data rate of 100 Mb/s data each can be packed into one HSD connection. A single HSD connection is enough for USB 2.0 and FireWire connections, whereas a double HSD connection is needed for USB 3.0.
My original post stated wrongly that M12 connectors cannot support data rates higher than 1 Gb/s. My thanks go to Martijn who pointed out in his comment that M12 connectors work happily at data rates of 10 Gb/s. I updated my post to reflect this fact.
M12 is perfectly suitable for higher data rates, up to 10Gb/s:
However M12 has a different problem in the Agricultural market. You need to tighten them with 0.6Nm to ensure proper sealing (IP69K). How to guarantee that in the field?
Thanks, Martijn, for pointing out my mistake about the data rates of M12 connectors. After an obviously too short search, I had only found M12 connectors supporting data rates of up to 1 Gb/s. Your links show that they can easily do 10 Gb/s.
You raise a good point about tightening the M12 connecting. At 0.6 Nm torque, the connectors would be so loose that they would fall out on the field. If the connectors are properly tightened to withstand vibration on the field, they would not be sealed accoring to IP69K. Is that the catch 22 you describe?