Summer Security: Guarding Your Beach Towel and Beyond
Imagine having a nifty device this summer that safeguards your belongings on the beach while you take a refreshing swim. This handy gadget prevents anyone from tampering with your items left on your beach towel. Not limited to beach use, it’s equally valuable for safeguarding your belongings in the office or workshop upon your return to work. Operating within a compact space and powered by basic primary cells or rechargeable batteries, the circuit generates a low-energy, high voltage ranging from approximately 200 to 400 V. While harmless to humans, it delivers a significant yet non-lethal jolt to deter anyone attempting to touch it.
Educational and Practical Fusion: A Valuable Lesson for Young Enthusiasts
Beyond its practical utility, this project holds educational value, especially for budding hobbyists. It provides an opportunity for young learners to explore a circuit that older enthusiasts. Particularly those experienced in radio and well-acquainted with valve technology, are likely to recognize. Apart from its practical application, this endeavor becomes a stepping stone for younger minds, blending hands-on learning with the wisdom of traditional electronic craftsmanship.
Simplicity in Design: The Basic Circuit Operation
Examining the circuit diagram reveals its extreme simplicity, containing only a single active element, a rather standard transistor. Functioning as a low-frequency oscillator, the transistor, denoted as T1, facilitates the conversion of the battery’s DC voltage into an AC voltage, which is then elevated through the transformer. Utilizing a center-tapped transformer, a ‘Hartley’ oscillator is constructed around T1. This oscillator design, named after its inventor Ralph V.L Hartley, was prevalent in the era dominated by vacuum tubes, before silicon electronics emerged.
Hartley Oscillator and Voltage Amplification
The ‘Hartley’ oscillator, a renowned L-C oscillator variant, gained prominence in the electronic world. It’s crucial for such an oscillator to employ the correct tapping point on the winding to ensure the accurate step-down ratio. However, due to the use of an off-the-shelf transformer, precise inductive tapping is compromised. The center position of the winding, although resulting in excessive feedback, guarantees reliable startup. Despite generating non-sinusoidal waves, this distortion is inconsequential for the circuit’s intended purpose. The output voltage, approximately 200 V peak-to-peak, can be directly utilized with the inclusion of current-limiting resistors R2 and R3, ensuring circuit safety.
Voltage Enhancement and Application Scenario
To further intensify the output voltage, a voltage doubler can be incorporated, producing approximately 300 V. This elevated voltage level significantly enhances the circuit’s deterrent effect. Resistors R4 and R5 are integral components of this configuration, ensuring safety. The circuit’s power consumption remains low, operating at a consistent few tens of milliamperes, regardless of its active status. For prolonged use, it’s advisable to power the circuit using AAA size Ni-MH batteries in groups of ten to avoid excessive expenditure on dry batteries.
Additional Notes on Measurement and Practical Application
When measuring the output voltage without the voltage doubler using a multimeter, the displayed value might be lower due to the non-sinusoidal waveform, causing challenges in interpreting the RMS value. An oscilloscope capable of handling high voltages is recommended for accurate readings. To apply this circuit for protection, attaching two small metallic areas, connected to the output terminals, on a surface like a beach bag’s handle is effective. Unwanted contact with both areas triggers the circuit, ensuring the intended protective measure. Care must be taken not to inadvertently trigger the circuit while disarming it during regular use.