Infrared TV Jammer

Engineer

Alexander H

Area of Interest

Mechanical Engineering

School

Galileo High School

Grade

Rising Junior

At BlueStamp this year I learned some skills that will be useful in the coming years. I learned about electrical engineering, power, and ICs. I improved my soldering skills and I learned how to use an oscilloscope.

Final Milestone – Breadboarded Oscillator

The TV Remote Receiver Jammer works by sending a steady infrared pulse at 38kHz, the same frequency as the TV’s receiver.  The “noise” coming from the jammer has no data for the receiver to decode, and the signal from the remote cannot get through. Before this circuit, I attempted to build from 2 schematics from the internet, and neither circuit worked properly. The final circuit that I made relies on a 555 timer to oscillate in astable mode between high and low power. which switches the IR LED on and off at 38kHz. The 555 timer has the trigger pin (pin 2) and the threshold pin (pin 6) shorted so the circuit has no stable states and oscillates between one and the other. These 2 pins are connected to ground through a capacitor, and connected to power through a 100 ohm resistor. The Vcc(pin 8) and reset (pin 4) pins are connected to the power. The ground pin (pin 1) is grounded, and the control voltage pin (pin 5) is connected to the ground through a 10nf ceramic capacitor. Pin 7, the discharge pin, is left floating. Pins 2 and 6 are connected to a potentiometer, which allows fine control of the frequency. I put a 150 ohm resistor and another potentiometer in parallel with the 1st potentiometer, which lowers the total resistance and allows finer control of the frequency. The output pin, pin 3 is connected by a 470 ohm resistor to the base of an NPN transistor acting as a ground switch. The emitter of the transistor is connected to the ground, and the collector is connected to an infrared LED, which is connected to the power by a 470 ohm resistor. The second potentiometer is not adjusted, as it is set so the first potentiometer can have optimal control over the frequency. The oscillation of the 555 timer is sent to the transistor, so when the wave is at a high point, the transistor switch is open, and when the wave is at a low point the transistor switch is closed. This allows for the LED to oscillate at higher power, as it is not drained by the rest of the circuit. I first had the circuit configured so the output pin connected directly to the LED, and that failed because the LED was not operating at high enough power, but was drawing enough current from the IC to heat it to unsafe temperatures. After adding the transistor switch, the IC no longer heated up, and the LED was noticeably brighter. I added the second potentiometer because one potentiometer did not give me enough control over the oscillation frequency. The second potentiometer changed my frequency range from between 0.5kHz and 90kHz to between 30kHz and 45kHz.

Starter Project

Mintyboost

This Mintyboost Phone charger is a USB charger for my phone. It provides 5 volts at 500 miliamps, and runs on AA batteries and has a USB port.  The  device converts 3 volts from the battery  to 5 volts for the USB charger through a  boost converter chip, which passes the energy through an inductor and increases voltage while decreasing current.  The schottky  diode causes the current to flow only one direction, into the phones battery. The  1/8 watt 3.3k resistor  resistor help improve  high current capability by resisting and limiting current. The 4 other resistors trick the iPhone into recognizing the charger as a supported device.  The inductor helps the boost converter chip by storing power in an magnetic field. The capacitors store and release electricity, and smooth out current flow. The battery pack holds the batteries, and the mint tin holds the entire assembly.

Over the course of this project, I learned about concepts such as induction, step up converters, electric resistance and its role in circuits, and the uses of capacitors. I also learned the useful skill of desoldering, which allowed me to rectify an error. I was not paying close attention to my work, and I had soldered a diode in the wrong direction. This served as a useful reminder to be more careful.

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