Frankenduino or Ueber Arduino ?
Well, both, kinda sorta eehhh….. But let’s take a step back.
A good while ago I designed and made an adapter board that combines a Teensy++2 and a WIZ812MJ Ethernet Module and currently the hardware in the photo below is installed and happily working in a Lighting system that employs five(5) HP LED shields (the older version). To the left is a TP-Link TL WR703n pocket router that connects to the WIZ812MJ Ethernet Module. An additional Ethernet Jack and Cable is used on the board to connect the I2C bus signals to another little adapter board plugged into the LED shield . This way 5 LED shields are daisy-chained together in the said LED lighting system.
I had to modify it from what is shown in the photo though and that was one of the reasons that I wanted to upgrade the concept for future installations. I had a Teensy3 as a Reward from the Kickstarter Project and as shown in the last post it works quite nicely and uncomplicated with the LED shield. It has to be said though that the shown configuration is NOT recommended. The Teensy3 is a 3.3V micro-controller and the outputs are not 5V tolerant. An I2C level converter should be used, e.g the one from DSS circuits or from Adafruit.
Also, the system above had some limitations. The Teensy++2 employs an Atmel processor that can run the I2C bus at max 400KHz, so it is not FM+ compatible, however all the components on the the HP LED shield are FM+ compatible (with the Exception of the temperature sensor!) so can be operated up to 1MHz. Also FM+ compliant components allow for much more drive current (30 mA vs. 3 mA) allowing for much higher allowable bus capacitance (4000pF vs. 400pF). In essence one can operate the I2C bus much more populated with devices and/or longer cable length at higher bus frequencies resulting in higher data transfer rates. The Teensy3 is able to operate the I2C bus at frequencies well in excess of 1MHz. Alltough it is not per-se FM+ compatible.
Another problem that I ran into and which is the reason I had to modify the hardware shown above, is that the power supply for the whole equipment to the left of the LED shield came from the little on-board 5V switching power supply of the HP LED shield. As long as it only has to operate an additional Arduino or Teensy that’s fine but the Ethernet & WiFi router hardware is more demanding and instead of the +5V from the LED shield I had to hardwire the VIN from the HP LED shield to an extra TSR-1xxx switched mini power supply to supply power to the Teensy++2 WIZ812MJ adapter board.
It would be nice as well to be able to just stack a processor board directly onto an HP LED shield or onto a stack of these, without the immediate need for an Ethernet cable.
So I started to lay out a board with all the necessities, but noticed it looked rather bare in terms of traces. The WIZ820io needs the usual SPI connections (+3.3V, GND, MISO, MOSI, SS, SCK) and the I2C bus only requires 3 traces (SCL, SDA, GND). That would have been a total waste of all the pins the Teensy3 has to offer and I decied to see if I could route at last some of these these to the usual Arduino pins on the periphery of the board. And the results of that effort is what I jokingly call an Ueber Arduino or perhaps its more a Frankenduino :