RC Helipad April 2013

The project for RC Helipad was done as a part of highschool's final exam at subject Information and communications technologies. It combined my love for RC helicopters and introduced me into the world of electronics.

The projects is divided into multiple parts:

Layout, construction and wiring of helipad
PCB circuit design in CadSoft Eagle and fabrication
Programming 8-bit PIC MCUs in Assembly

Layout, construction and wiring of helipad

It was decided to use 1m X 1m big board with red/green circle LEDs and while/blue LEDs which indicate the distance from a landing helicopter. The distance of helicopter would be detected using an ultrasonic sensor that would be connected to PIC16F505 which would output distance directly to blue/while LEDs. The second PIC16F505 would take care of red/green circling LEDs. A block diagram is shown in Figure 1. A plywood sheet was cut, drilled and prepared to be painted in white with black circle show in Figures 2-5.

Figure 1: A block diagram of RC Helipad

Figures 2-5: Drilling and painting of the helipad

PCB circuit design in CadSoft Eagle and fabrication

The circuit was designed in Eagle. Schematic and Layout of design. Inverted layout was then printed on transparent foil and a circuit was transferred to copper PCB board using phototransfer film on PCB. The film was developed and copper was etched using HCl acid to produce the final circuit. Last step was to solder all the components to the PCB. The steps are shown on Figures 6-9.

Figure 6: Schematic of RC helipad circuit

Figure 7: Layout of RC helipad circuit

Figure 8: Etched PCB of RC helipad circuit

Figure 9: Finalized PCB of RC helipad with soldered components

Programming 8-bit PIC MCUs in Assembly

Since we did not have any electrical engineering subjects on our high school I had taken programming advice from father's friend who introduced me to Assembly language. Also MCU's advanced C compilers were expensive any took a lot of MCU's resources.

That is why I have programmed the PICs using Assembly which is an excellent language to get understanding of how MCU's and higher computer languages work. Also 8-bit PICs are very good since they only have 33 Assembly instruction sets that are easily memorized.

The program was written in using Notepad++ and later compiled into binary using Microchip's MPASM. Programming the binary to PIC's flash was done using programmer K150.

Because of the simplicity of the MCUs there were multiple workarounds that needed to be made. The MCU supported had stack only 2 level stack meaning complex functions would need to be manually jumped. That is why a lot of label jumps without returning were used. Another disadvantage of simplicity is only a 12-bit timer so precise counting seconds, minutes and hours must be manually implemented. Lastly, MCU lacks interrupt handling, necessitating the use of pooling which lowers the capability of scheduling many tasks therefore dual MCUs were used, each executing their own task. Assembly code preview is shown in Figure 10.

Figure 10: A code snippet from project

Conclusion

The project presented me with many challenges, especially because I had to learn all the electronics from scratch. Therefore a few errors were made in the begging such as connecting NMOS's source connection to the positive terminal instead of negative since I did not understand the phenomenon of parasitic diode. Assembly language was also challenging to learn but it brought me a big insight into working principles of MCUs. With hard work I was able to polish all the issues and in the end the project was a success.