BOM and costs

Since the electronics section of my final project is comprised of several boards and components (the digits, the keypad, the bluetooth module, the rf module and the main controller), I will summarize here the full Bill of Material for all the different parts, then I will explain and document every and each electronic board in detail.

Work files links

Full circuits design

Eagle schematic and layout, and SketchUp render for all the electronic boards
Circuits.zip

7 Segments Digits

Since the main purpose of a scoreboard is obviously to show the actual score during a match, I had to design and build some kind of digit display. Volleyball matches don't exceed scores of 35 points, so the scoreboard need just 4 digits, 2 for team A and 2 for team B.

The simplest way of creating numeric displays, according to me, is 7 segments digits. But because my display will use WS2812B, that are daisy-chained, I need to rearrange the segments order, so to create a single digit as a single non intersecting line.

Once that problem is solved, it's just a matter of drawing the schematic and preparing the pcb layout to reflect that order:

3D Render

Work files links

Digit circuit design

Eagle schematic and layout, and SketchUp render for 7 segment digit display
Digit.zip

Bluetooth Module

The scoreboard will be remotely controllable with a specific Android APP. To establish the communication, it will use the Bluetooth SPP (Serial Port Profile). So I need a bluetooth module connected to the UART serial port of the microcontroller.

After a bit research I choose the Rayson BTM-222 module (check the BOM for more info), because it's cheap but powerful and has a wide coverage range. I created the custom library part for Eagle and the 3D model for EagleUp plugin.

The module schematic is really simple, because essentially it's just a breakout board for the needed signals, and a tactile switch to factory reset the module.

The signal BT_CONN will serve to inform the microcontroller when a Bluetooth connection is established. The 4-pin connector on the back is used to reprogram the original BTM-222 firmware, in case of need, so I didn't fit it on the final board.

3D Render

Work files links

Bluetooth module circuit design

Eagle schematic and layout, and SketchUp render for bluetooth module
Bluetooth.zip

RF Module

The scoreboard will also be remotely controllable with a small 2.4GHz remote. To establish the communication, it will use the Texas Instruments CC2500 radio module (check the BOM for more info). That radio module is really similar to the one I used for the Week 15 - Networking and Communication assignment.

I created the custom library part for Eagle and the 3D model for EagleUp plugin.

The module schematic is really simple, because essentially it's just a breakout board for the needed signals.

3D Render

Work files links

RF module circuit design

Eagle schematic and layout, and SketchUp render for RF module
Rf.zip

Keypad

The scoreboard will have a small keypad on the edge of the frame, to control its functionalities in case no remote connection is possible. To explore further the usage of less gpio as possible, I wanted to implement the keypad as a keymatrix.

THIS page explains very well the inner workings of the keymatrix technique. Moreover THIS document from Atmel, explains in detail the combination of keymatrices with interrupt driven GPIO.

3D Render

Work files links

Keypad circuit design

Eagle schematic and layout, and SketchUp render for keypad
Keypad.zip

Controller board

The brains of the scoreboard is a custom circuit board, designed to perform all the operations and functions.

It is composed as a modular board, so that every single module can be repaired, customized, improved etc. In the actual version, there are 5 modules:

• Power line distribution
  used to bring 5V across the frame in a more tidy way, and avoid wires running all along
• Power regulation
  used to regulate the input to 3.3V since the microcontroller, the bluetooth module and the rf modules all operates at that voltage
• Microcontroller and JTAG
  used as the main controlling unit of the board, with onboard crystal, reset switch and JTAG interface for programming and debugging
• Logic level shifting & keymatrix passives
  used to adapt the microcontroller output logic level toward the WS2812B leds at 5V
  used to avoid ghosting and masking problems on the keymatrix signals
• Logic signals distribution
  used to route logic signals (for RF module, Bluetooth module, keypad and digits) across the frame in a more tidy way

3D Render

Work files links

Controller circuit design

Eagle schematic and layout, and SketchUp render for controller
Controller.zip

Wiring and Assembly

The last step concerning the electronics of the scoreboard is to wire everything together and place the different boards inside the frame.

Having the power and the digital signal distribution modules, is quite simple to wire the several digit displays, and the other components without having a wire nightmare.

Finally everything can be secured in place inside the frame. I had little problems of clearance due to the JST connectors size (I forgot that one of them has 7 pins and not 6 as the others!) but I overcome those using a Dremel and some sandpaper.