RasPiComm Plus – an early insight into the ultimate Raspberry Pi extension board

ImageOur primary goal is to make the ultimate connectivity extension boards for the Rasberry Pi to connect it to the outside world. We think with the RasPiComm Plus we took the possibilities one step further.

Since I already wrote about our intention to develop a “RasPiComm Plus” I want to share details about this project in quite an early stage so you have the chance to comment on the design. We have a perfectly working prototype, so not as early as you might think now, but the RasPiComm Plus is a bit more complex than the RasPiComm, so we have quite a bit of software development work ahead of us. But first things first.

With the RasPiComm Plus we wanted to tackle some issues that are inherent to extension boards of that kind, flexibility and size being two of them. So what we did is to build an expansion board for expansion boards. Sounds complicated but it’s quite straight forward as you’ll see.

The RasPiComm Plus (our internal project name is Tiny Chameleon, you’ll see why) is a board with its own microcontroller (an ARM Cortex M3) and 4 edge-card connectors on the top side and the ICs and Raspberry Pi connector on the bottom. Now here is the cool part: You can plug up to 4 extension boards into those connectors depending on your needs. You can mount them with two screws so that the RasPiComm Plus is a wiggle-free, rock-solid customized extension board.

Here are the extension boards we want to start with:

  • 8 Inputs (5-35V), switching on 1/2 of the reference voltage with hysteresis
  • 8 Outputs (5-35V, 350mA/500mA peak with thermal shutdown and output transient protection/clamp diodes)
  • dual RS-485
  • CAN bus
  • GSM module
  • development board

Extension boards we are planning to make:

  • Isolated inputs and outputs
  • isolated RS-485
  • isolated/non-isolated RS-232
  • isolated CAN bus

To make these 4 connectors totally flexible we have a CPLD (complex programmable logic device) between the connectors and the microcontroller. So you are totally flexible which connector goes to which pins on the microcontroller and therefore you are able to plug any extension board in any slot!

As always, we want to provide a plug-and-play solution, so no playing around with the CPLD is needed, neither with the microprocessor, if you don’t want to. We will provide a serial driver module that will map the serial ports to /dev/tty devices as we do it with our RasPiComm board, and an API for the I/Os and the GSM module all hosted on github and on our repository for easy apt-get installation (which is also true for our RasPiComm drivers if you didn’t know yet!)

If you want to make your own microcontroller applications you can program the ARM processor directly from the Raspberry Pi via the serial port /dev/ttyAMA0 and the build-in bootloader. And if you want full control (ARM debugging and CPLD programming) you can use the JTAG headers (one for the ARM and the other one for the CPLD) to do your own custom solution. You want your outputs to react to inputs in 7 nanoseconds? No problem, program your logic into the CPLD and there is your ultra-fast “direct-wiring”.

You want a real-time system for your automation solution? Just program the ARM-processor any way you like using the extension boards mentioned above.

You need a stepper motor controller? Thats definitely on our list for further extension boards!

Here is a bottom view of the RasPiComm Plus where you can see the Raspberry Pi GPIO connector:


As you can see it uses the same piggyback approach as the RasPiComm even though it is longer extending over the borders of the Raspberry Pi. But that also has an advantage: you have 2 mounting holes and in fact you are not losing much space since the SD card of the Raspberry Pi is sticking out in this direction anyway.

Here are some features of the RasPiComm Plus:

  • 74x56mm
  • Real Time Clock with backup battery
  • ARM Cortex-M3
  • CPLD connected to the ARM, the Raspberry Pi and the 4 extension connectors
  • 5V supply connector
  • 24V supply connector
  • 24V-5V isolated DC-DC coverter (optional)
  • Raspberry Pi GPIO connector

Be aware that this is an early stage as I said, so there is no release date yet. But we would love to hear your ideas and comments on this design!

More infos about the RasPiComm Plus will follow soon so stay tuned!

Also have a look at our already availabe RasPiComm, the tiny Raspberry Pi piggyback board with RS-232, RS-485, real-time clock, joystick and more!

17 responses to “RasPiComm Plus – an early insight into the ultimate Raspberry Pi extension board

  1. Pingback: RasPiComm Plus – an early insight into the ultimate Raspberry Pi extension board | Frustrated IT Engineer

  2. Chris February 28, 2013 at 3:26 am

    What about using 3G instead of GSM?

    • Daniel Amesberger February 28, 2013 at 8:19 am

      Yes, good point. The thing is that 3G is more expensive and still a bigger footprint module. Since the extension modules are very tiny, small footprint modules are important.
      The GSM module is already extending 6mm over the edge of the Raspberry Pi. But I will have a look into that.

  3. Chris March 1, 2013 at 3:05 am

    Sounds good, our experience with GSM was not that good and to offer better reliability we always use 3G. I understand that the costs will go up

  4. Dion Marriott March 4, 2013 at 4:02 am

    I’m really very interested in this board.

    I have it in mind as an all-in-one solution for a distributed control and feedback network based on CAN bus, with the Pi providing human machine interface functionality.

    Have you decided yet on the physical CAN bus configuration; i.e. single or dual connector, D-sub or RJ45 or something else?

    Also, any plans for a 1-wire expansion board?


    • Daniel Amesberger March 4, 2013 at 10:16 am

      Glad you like the board!
      We already have the PCB design of the CAN-Bus. Currently we plan to have a D-Sub9 connector with two CAN-bus interfaces. Usually we would only populate one CAN-bus since the ARM processor only offers one CAN. But we chose an ARM which is footprint-compatible with a better version which would offer 2 CAN-bus interfaces.
      I already thought about 1-wire, I think it might be possible to do a 1-wire to I2C in CPLD logic, thats why we didn’t yet make a board for it. But I still have to check.

      • Dion Marriott March 4, 2013 at 12:39 pm

        In truth I was thinking just two physical connections so that the board can be inserted into a network (ie between two other nodes), rather than as an end node. That would require the not-so-better ARM and a single CAN driver circuit.

        Maybe with two D-subs mounted, it is possible to common the connections?

        Anyway, I shall await developments as they happen, including any I2C to 1-wire ideas.

  5. daviewales March 11, 2013 at 4:47 am

    So… Does that mean it’s a Chameleon Circuit?

  6. Ron Arts March 12, 2013 at 3:19 pm

    I would very much like to see an XBee board. Though EVE Alpha offers something similar, I like this idea for having 4 module slots available.

  7. Pingback: RasPiComm Plus กำลังจะมา | Raspberry Pi Thailand

  8. qtfp May 28, 2013 at 8:44 am

    Great idea! wait for it !

  9. Rolf November 6, 2013 at 1:20 pm

    Hallo Daniel,
    wie weit ist das Projekt fortgeschritten? Kann man schon etwas über den geplanten Preis sagen?

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