Assembly

Table of contents:

The wooden chessboard

This is a quite simple folding wooden chessboard that, once opened, is about 27cm side and 2cm high. The square is 3cm.

PCBs for magnetic sensors

I've used perforated boards (Single-Sided with Single Hole per Pad), although I admit that it is not the best choice, because they are quite expensive.

As usual, one of the most important things in the design is to choose the right combination of sensor/magnet, as well as the sensor position relative to the center of the square. For this purpose, the actual thickness of the board is simulated, and we move the sensor (reed switch) above the diagonal of the square, to find the optimal position.

For more information on this process: SolusChess USB - Magnetic Sensors

This is the arrangement that works best for me, for the chosen components and this square size:

I discover with surprise that the chessboard is not completely symmetrical, so I decide to use vegetal paper to correctly position the reed switches:

I cut the PCB for a perfect fit, and then I mark the position of the reed switches with a marker pen:

This is the wiring diagram of the 64 reed switches with its 64 diodes. For more information on this subject: SolusChess USB - Sensor Matrix

Components used...

  • Reed switch: MKA-14103

  • Diode: 1N4148

In assembling I find that the glass bulbs of these reed switches (MKA-14103) are broken very easily, and that when installing the PCB inside the chessboard, it's possible that they may break if pressure is performed from the back. I decide not to risk, by placing rubber spacers (3mm thick) that prevent reed switches to touch the wood. It will be a gap of about 0.5mm

Wiring and components

For general aspects on how to connect the Teensy board: SolusChess - Teensy USB Development Board

Here you can see the schematics of this version with Bluetooth support.

External Pair Button

If "Pair Button" of Bluefruit board is not accessible from outside, for example through a small hole in the cover, the addition of an external push button may be required. It will be necessary to press this pushbutton every time you want to change the paired device.

This pushbutton (Normally Open type) must be connected between PB and 3V pin, as shown in the following diagram:

We began installing LEDs, pushbuttons, mini-USB connector, etc.

As seen in the diagram, the USB cable has to be split in two:

  • Data (D+, D-) to Teensy

  • Power (VCC, GND) to Battery Charger

An easy way to do this is by using a mini-USB female-to-male cable, cutting the power wires (usually red and black), connecting them to the battery charge board. I have chosen to use new connectors and wiring by hand.

Since we had to split the sensor matrix into two parts, because it's a folding chessboard, a ribbon cable is used to interconnect the two PCB, as well as to connect one of the two LEDs. We can use a PC cable, those used for connecting IDE hard drives: we need 14 wires.

Once the first part (rows 1-4) is complete, I use a piece of MDF as cover, 2.5mm in thickness:

And I continue with the second part (rows 5-8):

I made a separating tray with a 3D printer, on which all the electronics will be installed.

Main components...

  • Microcontroller: Teensy++ 2.0

  • Bluetooth Module: Bluefruit EZ-Key

  • Intelligent charger: Adafruit USB LiIon/LiPoly charger - v1.2

  • Rechargeable Battery: Lithium Ion Polymer Battery - 3.7v 1200mAh

The components are fixed with double-sided adhesive tape. Also thermic glue is placed on the corners for added safety. The thermic glue is easy to remove, if necessary, by heating it with the tip of a soldering iron.

Start-up

We upload the firmware to the Teensy board, with The Teensy Loader Application

Then we must check that everything is working properly, that the battery is charging, etc.

On this side of the chessboard, the initial idea was to use a MDF cover with only one hole for the on/off switch, but then I thought it was a better idea to install "tiny windows" for the LEDs (Bluetooth, Charge, etc.).

Indicators, using LEDs incorporated in the different boards:

  • EXT. POWER: In red when the intelligent charging system is powered through the USB connector.

  • BATTERY: Orange indicates the battery is charging. Green that the battery is 100% charged.

  • BLUETOOTH: Indicates the "pairing" status (see animated image below).

This animated picture lets you check the status of the pairing, between chessboard and host computer.

This image is an animation. If it remains static, open it in another browser tab.

Checking the chessboard is closing properly, and that the ribbon cable is bent correctly.

Pair button

Access to the Bluetooth Pair Button has been added at the last minute: