The transmitter module is responsible for transmitting the actions of the push buttons and the LCD TFT screen. It also stores the control software for different driving modes. The transmitter module "Slotpiral R-evolution" slot controller includes the following functional blocks:
Figure 70. Block diagram of the hardware architecture of the transmitter module.
PROCESSING UNIT
The transmitter module is composed of a front panel which acts as a control interface for handling the push buttons arranged on its surface, directing the information received after the activation of each push button to the next functional block architecture. It also has a LCD TFT color screen showing the different driving modes available in slot con- troller.
The processing unit in transmission is responsible for receiving information on the front panel and through the ATmega328 microcontroller Arduino platform different signals are processed. The microcontroller is equipped with a software that manages the opera- tion of the slot controller, with different driving modes available.
Furthermore, the transmitter module is responsible for transmitting information in the front panel push buttons through the Tx antenna, for later analysis in the receiver mod- ule.
7.2.1 Front panel design
In the process of designing the front panel, different prototypes were made until the final implemented design.
Firstly, a controller with inverted U-shaped, inspired by video game consoles, with a LEDs bar in the center indicating the speed of the slot vehicle was designed.
Secondly, the design was refined by reorganizing the push buttons of throttle, brake and turbo to be operated with the fingers of the right hand, and pass and mode push buttons, to be operated with left hand. LEDs of the main actions were also included.
Finally, the design was modified and inspired by a steering wheel, giving to the slot controller more ergonomic. The layout of the buttons was changed and a TFT LCD col- or display was implemented to improve the graphical interface.
The following figure shows the evolution of the design of the front panel with the im- provements discussed:
After performing the virtual design of the front panel, the printed circuit boards were designed. The printed circuit boards of the front panel were divided into 4 modules or shields to allow a modular manufacturing and facilitate the detection and repair of breakdowns.
Button L shield: it contains push buttons for pass and driving mode selection, to press it with left hand fingers.
Button R shield: it contains acceleration, brake and turbo buttons, to press it with right hand fingers.
Central shield: it contains the necessary connections for the TFT LCD display, power and processing unit.
XBee shield: it contains the connections required by the radio frequency Tx an- tenna and voltage regulation.
Using the software tool OrCAD, the schematics attached in the Appendix C (p. 143) and the routing tracks of the printed circuit boards were designed (Figure 72).
Once finished the manufacturing process of the printed circuit board by chemical etch- ing, the holes were made on the board and then the electronic components of the front panel were inserted using through-hole technology.
After cutting the remaining edges of the printed circuit board and cleaning impurities resulting from drilling and cutting process, it is necessary to continue with the next phase of the implementation of the front panel, the welding process.
As a precaution, continuity checks are carried out on the tracks of the printed circuit boards and copper remains are removed to prevent short circuits. For welding process are used flux paste, soldering wire composed of 60% tin and 40% lead, and a solder with fine tip.
Figure 73. Button L, central and button R printed circuit board with components. The minimum electronic components used to implement all shields on the front panel are the following:
Push buttons: 5 push buttons are required, one for each action: throttle, braking, turbo, pass and mode selection.
Resistors: 5 resistor of 10kΩ are necessary for the push buttons circuits.
Pin headers: 28 pin headers spaced 2.54 mm are required to connect the differ- ent shields, 4 for the XBee shield, 4 for the button L shield, 5 for the button R shield and 15 for the central shield.
Pin sockets: 40 pin sockets spaced 2.54 mm are necessary, 10 are required to connect the TFT LCD screen to the central shield and 30 are used to connect the Arduino Nano to the central shield.
Once all the welds of the PCB on the front panel are made, the conductivity is checked by a multimeter. Then, the shields are connected by cables and perfect operation is checked. Finally, after checking that it works properly, all circuits are introduced into the case previously designed.
7.2.2 Processing unit design
The processing unit is used at the open source platform Arduino, specifically the Nano model, explained in detail in chapter 5.
This platform is equipped with Atmel ATmega328 microcontroller and has the electron- ics necessary to connect different inputs and outputs on the pin headers arranged for this purpose on the side of the printed circuit board. One of the advantages already high- lighted in the previous chapter, is that Arduino only requires a USB cable to connect to a computer and program the microcontroller so quickly.
In this section, the processing unit is designed to hardware level, indicating inputs and outputs used by the other functional blocks of the transmitter module. The main connec- tions of the Arduino Nano platform are shown in the figure on the next page.
Figure 74. Connections diagram of the transmitter processing unit.
7.2.3 Power source design
After studying the energy needs of the transmitter module conducted in chapter 5 and the laboratory tests carried out, it is demonstrated that the power source that best suited to the project is a 9V battery. To implement power source, a switch connected in series with the 9V battery was installed, to turn on and off the slot controller easily. A battery case made of plastic was used to secure the battery in the project.
7.2.4 Communications design
To communicate the transmitter module of the slot controller, XBee shield is used. The shield is equipped with an XBee Series 1 with integrated radiofrequency antenna. This communication system uses secure point to point connection with a range up to 30 me- ters inside buildings, enough distance for a slot controller purpose. The actions of the front panel are processed by the Arduino Nano platform and serial data is sent by the XBee transmitter module in real time.
XBee receiver and transmitter modules were properly configured with software XCTU, linking their serial numbers to establish a secure communication [52]. The transmitter communication system is implemented by an XBee Series 1 module connected to the pin sockets of the XBee shield spaced 2 mm. Finally, the XBee shield is connected to the central shield with 4 connectors, as is shown is the Figure 75 on the next page.
Figure 75. Connections diagram of the XBee shield.
7.2.5 Final implementation
In the final design stage of the transmitter module of the slot controller, the different functional blocks described in previous sections are assembled. The connections be- tween the modules are performed using female to female wires, because all shields have headers pins.
The following picture illustrates actual result of the connections made to implement the transmitter module of the “Slotpiral R-evolution” controller:
Figure 76. Connections of Slotpiral R-evolution transmitter module.