Tesla Coil Security System
|Sponsors||Dr. Herbert Hess|
|Team Name||Shock the Nation|
|Duration||Fall 2019 - Spring 2020|
The goal of the project is to create a doorway security system powered by a Tesla coil that will shock unwanted intruders and prevent their entry.
Provide an alternate safety device for preventing access to a room or house, using a tesla coil design. This design should electrically shock intruders with the same voltage as a standard taser, with the intent to attend intruders but not injure. This shock should occur four times a second and be discreetly positioned so the intruder can not easily spot it. We also need to be able to direct our electrical arch in a specific direction.
What better way to get someone's attention than a sudden 50,000 volt shock? This contraption is designed to keep unwanted intruders from entering through a doorway for whatever reason. Using a Tesla coil, the intruder will be shocked upon reaching for the door handle.
This system could be used for any doorway. With an aim to steer away intruders without serious injury, safety features are implemented to insure not only the intruder(s) but also the owner(s) of the system are at low risk of severe injury.
With both mechanical and electrical design techniques, the Tesla coil security system is designed to optimize effectiveness as well as convenience using an appropriate Tesla coil, touchscreen, material selection and geometry among other design considerations.
- Team Contract
-An outline of the roles for each member of the group
-Maximum budget for our design is $1000
-Outlined schedule of our project including design review dates and deadlines
- Product Requirements
Files shown under "Additional Documentation"
User Interface Design Specifications
- Be able to arm/disarm the security system
- Produce an electrical shock protruding from the door handle to the intruder
- Sense an approaching intruder
- Use of a mechanical arm for demonstrative purposes
- Retrofitted door handle to direct the electrical arch
- Use of a wooden door frame because of non-conductive properties
- Magnets of appropriate strength to keep the door closed rather than a latch assembly
- Operate shock an a frequency of around 4 Hz
- 2 inch arch from the door handle
- Touchscreen security for arming/disarming the system
- Sensors for detecting an incoming intruder
- Appropriately sized Tesla coil
- Scare away the intruder without serious injury or death
- Minimal risk of unwanted shock while the system is armed
- Effective arming/disarming feature
- Keep the cost under $1000
Mechanical Design Considerations
From a mechanical perspective, the geometry and material selection of the door, door handle, and frame is crucial to optimize the electrical arch protrusion.
A wooden door and door frame are used because of the fact that wood is practically non-conductive. This is important so the electricity produced from the Tesla coil does not arch to the door or frame at any point along the electrical pathway. The type of wood is not important and can be selected to the discretion of the system owner.
Rather than using a traditional latch assembly to open and close the door, magnets are implemented on the door edge as well as the corresponding door frame positions to hold the door in place while it is closed. A dead bolt may also be implemented for a more secure lock when it is wanted or needed.
The door handle a more complicated design. Using a 3D printer, the handle is made with ABS plastic. A handle cap made of copper is then secured onto the tip of the plastic handle for conduction of the electric arch. Small conductors made with electroplated silver are implemented. This will help increase the surface area of protruding shock from the door handle.
Electrical Design Considerations
The electrical design is most important for the safety of the system as well as the effectiveness. The Tesla coil must be able to be armed and disarmed as well as provide a shock sufficient enough to scare away the intruder without seriously harming them.
A touchscreen located outside of the secured room will be available for arming and disarming the system. By entering a PIN, the user will be able to choose the state of activity the system is in. This is crucial in the fact that it will allow people to walk in the door without being shocked.
The Tesla coil is perhaps the most important piece of the system. The geometry of the coil itself as well as material selection of wiring and infrastructure play a role in the overall performance and output of the system. The desired output voltage is dependent on the height, number of wire turns, resistivity of air, and other things. An input of 350kV is required for this particular system to achieve an output voltage of around 20kV. This means that the intruder will be shocked with approximately 20,000 volts--around the same as a typical taser.
- Our first consideration for this project was to use a Jacob's Ladder. This has two conductive rails that would be attached on either side of the door frame. The bottom of each rail would be bent towards each other at the bottom of the door to decrease the distance between the two rails. These rails would be attached to isolated hinges that would allow them to be moved to the side during daily use of the door but could be locked in place when the door was ready to be armed. A high voltage transformer would be used so an electrical arc could be formed across the two rails at the closest point and the arc would travel up the two rails. This device would use motion detection using a microprocessor with a touchscreen interface and ultrasonic sensors. There would also be a switch in the hinges so the system could only be armed when the lower portion of the rails were in the correct position to be armed.
- The second design considered was the implementation of a controlled electrical arcing door handle. This would be accomplished through the use of a Tesla coil circuit. These circuits use a high voltage transformer to step up the voltage. This high voltage then charges up a capacitor bank. When the capacitor bank reaches its peak voltage, a voltage that is high enough to arc through a small distance in the air, a spark gap will fire. A spark gap is a high voltage switch that uses a high voltage arc as a switch. When the spark gap is firing it allows the primary coil of the Tesla coil to gain some energy. This energy is oscillated between the capacitor bank and the primary coil. While this oscillation is occurring some of the energy from the primary coil is passed to the secondary coil of the Tesla coil. The secondary coil then oscillates its energy to the specially designed door handle. With each cycle more charge is collected in the door handle until it has enough charge to arc out.
- As the second design was expanded upon the internal mechanical components of the door handle were identified to be an issue. As such, designs for the internal components were considered but found that using these designs may cause interference with the operation of the Tesla coil. Therefore, a second design was considered that used magnets at the top and bottom of the door to hold it in place and the handle itself would be a ‘stand-alone” piece of equipment.
- We decided to go with the design with the arcing door handle. The two rail system had some design challenges and safety concerns. In order for our rail system to work it would have needed a higher voltage to be able to cross the gap of a doorway. We were concerned about the risk of fire with the two rail system. To hold the door in place magnets were selected for their ease of use and lack of potential interference with the handle.
- For the handle the second design of two dissimilar metals was selected because the equipment to cast the handle was not available to us and to export this to an external company would have not been within the constraints of the budget.
- To manufacture the contact points and dome shape the part would be CNC lathed. The former would copper that would be electroplated onto aluminum. The latter would be silver that would be electroplated onto aluminum. To hold the three pieces of the handle together and epoxy would be used. The handle would then be mounted to the door using 3D printed rose covers with nylon screws.
- The Tesla coil will be controlled via a raspberry pi 3b microprocessor. This control circuit consists of a touch screen with different modes of operation available to the user. Modes such as arm, disarm, test, and exit. When armed is selected two ultrasonic sensors will be activated. They are measuring distances and comparing each new distance to the latest distance measured. If the newest measurement is smaller than the older measurement it will close a relay which then provides power to the Tesla circuit described above. If the ultrasonic sensors detect no movement then the relay will close and remove power from the Tesla coil. The command test will close the relay to provide power to the Tesla coil. The command disarm and exit will open the relay. Exit will go one step further and close the program.
- The door knob will be made up of three parts which will have a dome shape on the front part that will be made of a highly conductive material. We will have embedded contact points around the dome also made of a conductive material. The idea was that we will get an arc from the dome to the contact points. Allowing us to control where the arc will go.
- Our design consists of a transformer for stepping up the voltage with the use of two frequency matched LC circuits. Energy is passed from the first LC circuit to the second LC circuit through a spark gap. A spark gap is a switch which consists of two electrodes separated by air. This energy transfer is most efficient when the two LC circuits have matching frequencies. The first consists of our capacitor bank and the primary of the Tesla coil. The second LC circuit is made up by the secondary of the Tesla coil and the capacitance of the top load. The top load in our case is the specially designed door handle. This design allows for our door handle to produce high voltage electrical arcs.
| Danny Pierce
Major: Mechanical Engineering
Major: Electrical Engineering
Major: Electrical Engineering
Major: Biological Engineering