Monthly Archives: February 2013

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!

Use RS485 from your Raspberry Pi via /dev/ttyRPC0!

Our RasPiComm device driver is available now! You can now use /dev/ttyRPC0 (RPC for RasPiComm) to access the RS485 port. Find the sourcecode on Github!

Go to our community forum if you have any questions!

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