The goal of this project was to create something fun and interesting which utilizes a variety of different hardware sensors and components. Along with that, I wanted to give readers example code which utilizes current technologies like mesh networks, displays for embedded systems, and accelerometers, with intention that you yourself can go off and do amazing things with the technology. In this project, I put a twist on a classic arcade game utilizing Arm Mbed devices and components. I also included some stripped down sample code for the drivers and libraries, to assist you in getting the hardware working in any other projects you may have.
To see the project in action, check out the accompanying YouTube video. Other cool projects can be found on Arm Mbed's facebook page as well, check them out.
In this project, there are three different microcontrollers, consisting of a master and two slaves. The master is responsible for bringing up the mesh network, assigning IP addresses to its slaves, and updating the game screen. The slave devices are issued out to game players, and are used like ping-pong paddles.
When a player raises and lowers their paddle, the slave device's accelerometer data is transmitted to the master, and the master will update the player's paddle location on the screen based on that data. The players try to get as many points as possible by sending the ping-pong ball into the other player's goal. Once the max score is reached, a winner is determined and the game ends.
The devices in this project communicate with each other using a newer 2.4GHz wireless protocol named Thread, which has recently become an industry standard and is backed by an alliance of big name companies. The cool thing about this mesh network is that it does not require any external router or Internet connection to communicate between the devices, as it is all self contained. For more information on Thread, an introduction can found here.
In order to build this project, you will need the following items:
- FRDM-K64F (x3).
- 6LoWPAN shield (x3).
- ST7735 LCD display.
- Male header pins.
- Female/Female jumper wires.
- Male/Male jumper wires.
- Soldering Iron and solder.
Optional items to make the devices battery powered:
- PowerBoost 500 charger (x3).
- LiPo battery (x3).
- 6in USB cable (x3).
This section explains all the hardware, modifications, and connections needed to build the master device. First, I will explain how to solder the necessary headers to the board. After that, I will show you how to connect the screen to the device with a ribbon cable of wires. Finally, I will instruct you on attaching the 6LoWPAN shield used for mesh networking.
The master device requires use of two different SPI module blocks found on the FRDM-K64F. The first SPI block is consumed by the 6LowPAN shield. The second SPI block is used by the ST7735 LCD screen. The second SPI block is not initially pined out on any header of the FRDM-K64F, therefore, an additional header needs to be soldered to the board. The location of where the header needs to be soldered is shown in the image below.
Now, prepare some male pin headers into a 2x4 configuration. Below is what they should look like.
Below is what the device should look like after soldering the pins to the board.
The pin numbers and pin names for this new header is provided below. The numbers in this image corrispond to the numbers printed on the board's silkscreen next to the header.
Now with these additional SPI pins available, you can connect the ST7735 LCD screen to them with jumper wires!
The pinout table below shows how you should connect the ST7735 LCD to the FRDM-K64F. Note, the 2x4 header that you soldered onto the FRDM-K64F only has one Gnd pin, and no +3.3V pins. The remaining Gnd and +3.3V pins that are required can come from any other acceptable power/gnd pin found on the FRDM-K64F.
| ST7735 LCD pin | FRDM-K64F pin |
|---|---|
| LITE | +3.3V |
| MISO | PTD7 |
| SCK | PTD5 |
| MOSI | PTD6 |
| TFT_CS | PTD4 |
| CARD_CS | Unconnected |
| D/C | PTC18 |
| RESET | +3.3V |
| VCC | +3.3V |
| Gnd | Gnd |
After the screen is fully connected to the board, the last step for the master deive is to connect the 6LoWPAN shield to the FRDM-K64F. The 6LoWPAN shields have Arduino R3 headers, and should connect easily to the FRDM-K64F. The master device will now look something similar to the first image in this document.
The only hardware needed for the slave devices are two FRDM-K64F microcontrollers and two 6LowPAN Shields. Simply attach the 6LoWPAN shields to the headers of the FRDM-K64F. The 6LoWPAN shields have Arduino R3 headers, and should connect easily to the FRDM-K64F.
I recommend powering the devices via batteries so that they are untethered during play. This makes playing the ping-pong game a more authentic experience. Below is an image showing how I connected the PowerBoost 500 charger and LiPo battery to the FRDM-K64F devices. First I zip tied the LiPo battery and PowerBoost 500 together with a single zip tie. I then zip tied that bundle to the bottom of the FRDM-K64F. These PowerBoost 500 chargers are awesome, as they can charge your LiPos and provide a steady +5V for the FRDM-K64F. If you are feeling adventurous, it is possible to solder wires directly to the board, so that you do not need any USB cables. Feel free to get creative here!
Clone the repository onto your computer. Make sure mbed CLI is installed with the requirements as shown in this video.
The directory structure of this repo, along with a description of each of the different directories is below:
- display - Sample code, drivers, and libraries for the ST7735 display.
- images - Images that are used within this README.
- master - Code that gets flashed to the master device.
- motion - Sample code, drivers, and libraries for the accelerometer.
- slave - Code that gets flased to the slave devices.
The directories motion and display are simply starter code I added to assist you in designing similar projects. To replicate the project that I made in this document, you just need to compile the code for the master and slave devices. To compile code for these devices, run the following commands from the root directory of this repo:
cd master
mbed compile -m K64F -t GCC_ARM
cd ../slave
mbed compile -m K64F -t GCC_ARM
Once all the files are compiled, you can then drag and drop their resulting binaries (.bin file) onto the respective master and slave devices.
After the master and slave devices have been flashed, you can power them up and hand a slave device out to each player. All three devices should start off with a blinking red LED to begin with. The red LED represents that the boards are waiting for an IP address. The master device will be the first to acquire an IP address, and will cause the LED to blink green. After the master has acquired an IP address, it will then assign IP addresses out to its slaves, resulting in a green LED on the slave devices as well.
When all the devices LEDs are blinking green, the mesh network is fully configured. Next, it is time to pair the players to their paddles. Have Player1 press the user button found in the red rectangle in the image below. This same user button will be used to serve the ping-pong ball later in the game.
After Player1 presses the user button, the screen on the master device should update saying that Player1 has been paired. Player2 should then press their user button as well. Once both players have their paddles paired, the game is ready to begin. Any player can now press the user button found on the master device to start the game.
When the game starts, Player1's paddle will be on the left side of the screen, and Player2's paddle will be on the right. Players can control the paddles on the screen my moving their slave devices up and down in an arc, as seen in the image below. Internally, the slave devices are capturing thier x,y, and z coordinates using their accelerometers. After capturing enough measurements, the values are averaged and then broadcasting over the mesh network. The master device will receive that broadcast, determines who sent the message, translates the x,y,z data into an angle, and then updates that player's paddle on the screen based off that angle. If the device is at 180 degrees, the game will draw the paddle at the very top of the screen, and if at 0 degress the paddle will be on the bottom.
Player1 starts with the ball, and should press the user button on their paddle to serve. After serving, the ball will bounce back and forth between the paddles until a goal is made. Once a goal is made, the player that just got scored on will now be in possession on the ball, and must serve. The game continues this way until the max score is met, and then a winner is announced.