Around the Adafruit Playground I: a "Motherboard" With Expansion Port

The Adafruit Circuit Playground cards (Classic, Express, Bluefruit) are nice boards for learning with. They directly provide NeoPixel leds, push buttons, and several sensors like temperature, luminosity, even an accelerometor, etc.. Furthermore, one can connect supplemental hardware via alligator clip pads. This solution if however not very robust (risk of shortcuts, loose connections...).

Dave Astels has proposed a nice prototyping shield solution:

https://learn.adafruit.com/circuit-playground-shields

Here is an alternate approach, which has the advantage of also provinding a protection for the board, in form of a case enclosure, inspired from Ruiz Brothers ones:

https://learn.adafruit.com/case-for-circuit-playground

Adafruit Plaground Classic, Express, or Bluefruit

Equipment to make printed circuits

3D Printer

Female DB15 connector

3 mm diameter, 6 mm long screws, nuts

We want to be able to expand the Adafruit Playground capabilities, by connecting sensors, actuators, displays etc... to the board.

So, we want to replicate the 4 general purpose I/O pads #6, #9, #10 and #12, the serial communication port #0 RX and #1 TX, and the I2C port #2 SCA and #3 SCL => 8 pins needed (see images above. Images are from Adafruit Circuit Playground website: https://learn.adafruit.com/introducing-circuit-playground/guided-tour)

Also, we will need Ground and 3.3 V to power external components, but VBatt can also be very usefull => 3 pins needed

8 + 3 = 11 connection pins needed. The very classical DB15 connector will do the job.

Then, one has to make a choice, connecting Playground pads to DB15 pins. The upper row of the connector has 8 pins, so it seems logical to attach the 8 I/O ports. From the lower row (7 pins), we need only 3 pins, so one could take pin 9 for 3.3V, pin 15 for ground and pin 12 for Vbatt.

See pdf file below for the complete pinout.

Having decided the DB15 - APC connection, the design of the "motherboard" was done in KiCad. An hexagonal case was chosen, but the design could be adapted to a square one for example.

Unfortunately, Instructables does not allow KiCad project uploading. The pdf file of the mask if provided below. I will later provide a link to download the whole KiCad project.

When the circuit has been etched or engraved, cut and drilled, or manufactured by a third party, one can install it in its case, to check it fits well.

A case has been designed, adapted from Ruiz Brothers's hexagonal case.

Here are the step files for 3D printing the case and the cover. There is no peculiar specification, PLA printing works well for such cases.

Because the board will be use for sofware development, use of battery is supressed, so the location for a switch in the original case. In case of bad contact for VBatt (see Step 4), just cut the 4th support originally located in the red circle

You can downaload the case and cover stl file here:

First you have to solder the DB15 connector (1st and 2nd image). Beware when inserting the connector in the printed board, tolerances are very tight, and it's easy to bend/break a pin. Be precise when soldering, as pin layout is quite dense.

Then, just bolt the APC onto the board (Images 3,4), this will ensure electrical contact between the APC and the board. For fixing the board, 6 mm long, 3mm screws just work nicely (sorry, I am not familiar with drunken lobster's units :-). Apparently 1/8" screws are the closest in dimensions, but I could not test).

The case of VBatt is a bit peculiar, as direcly screwing onto the case does not always ensure good electrical contact. So the choice is to cut the 4th support of the case (see Step 3), and put a screw + nut (Red arrow on Image 4).

Note: to avoid potential shortcuts, you may also protect the circuits at some places were screws are very close to circuit lanes. You can just use scotch tape (see Images 2 and 4).

Test and re-test to check that all connections with DB15 are OK, and that no shortcut did appear.

Finally, screw the board into the case, using the 3 remaining holes and 3 supports (Image 5) and put the cover (Image 6).

When ready, you can use the board as a stand alone, or connect it to a prototyping board, or develop extension boards that fit your needs.

As an example, the image shows a "test board" developed to check that everything is fine with the "motherboard" :

1. Red and green leds are lit if VBatt and 3.3 V are OK.
2. A Microbot MR002-001.2 USART <-> RS32 converter permits to test the serial port #0 and #1
3. A 3.3V SR04 ultrasonic transducer is connected to #10 and #9
4. Two 5 kOhms potentiometers are connected to #6 and #12 to test anolog inputs
5. an Adafruit Quad Alphanumeric 14-segment Display is connected to I2C, 5V for powering leds, and 3.3V to set the logic level for communication to the Playground (https://learn.adafruit.com/adafruit-led-backpack/0-54-alphanumeric-9b21a470-83ad-459c-af02-209d8d82c462)

One just has to make the connection from the DB15 to the breadboard. One can use Dupont cables, here an old hard-disk cable had been modified. In a next part, we will see how to design extension boards.

Many thanks to my colleagues Joël Lambert for the case modifications, and Jordan Veron for printed circuit design !!!