Computing stuff tied to the physical world


Bridge Board – caveats

In Hardware on Dec 2, 2010 at 00:01

There is some complexity lurking in the design of the Bridge Board, which in turn may lead to some head scratching, I’m afraid…

That complexity comes from the fact that not all I/O pins are always available.

Let’s start with an overview of the different pin groups:

Annotated bb

The basic idea is that when you connect all four port headers, then you’ll get access on the breadboard to all the pins marked above in RED. This is the most common usage, and main intended use of the Bridge Board. Note that DIO2, DIO3, AIO2, and AIO3 are available on multiple pins.

So if you follow yesterday’s post, you can use all the pins shown in red as is. The main benefit being that you can easily access the main 8 I/O pins, and that port 2 is in fact replicated in the same layout on the breadboard if you want to hook it up to JeePlugs.

If all you need are the leftmost 16 pins – you can skip the rest of this post.

The remaining pins takes a bit more explanation and preparation, and requires adding some more header on the Bridge Board as well as on the JeeNode! – here’s the summary:

  • to use the 6 SPI/ISP pins marked in BLUE, add the 2×4 pin header on the right
  • to use 4 more I/O pins marked in GREEN, add a 8-pin header on the left (the middle 6 are actually enough)
  • to use FTDI, add the 8-pin header on the left (only JeeNode v4: also the 2×4-pins on the right)

That last option also requires soldering in a 0.1µF capacitor if you want to include the reset-on-open capability for easy uploading. It’s mostly intended for use with a JeeSMD, which does not have an upload capability of its own.

There is a reasoning behind all this madness:

  • The leftmost 16 pins on the breadboard were the main design goal for this board.
  • The middle 13 pins (IRQ to B0) match the layout need for the Ether Card.
  • The rightmost 20 pins are compatible with both Ether Card and Carrier Board.
  • The Bridge Board is compatible with JeeNode v5 and v4, JeeNode USB, and JeeSMD.

The two LEDs are brought out on separate pins and always available – on the LED1 and LED2 pins, respectively. They are very efficient and require only a few mA to shine brightly. You can hook them up to any I/O pin or other 3.3/5V signal on your breadboard. They make a great debugging tool when the going gets tough.

The push-button at the top of the board is also always available on the BTN pin. It is connected to ground, so pressing the button shorts the BTN pin to ground – you can use the internal ATmega pull-up and some software debouncing to read out this button.

The button can be used as reset button if you have the RST pin, which is right next to it, hooked up to the JeeNode. This requires either the 8-pin PSIX header or the 2×4-pin SPI/ISP header to be hooked up, as described earlier.