This is a simple 555 timer based circuit which can jam IR (Infrared) communications like TV remotes, when I first made the circuit (October 2011) it was a bit iffy at jamming IR and eventually stopped working for some reason, it wasn’t until recently that I brought a mini DSO and found out it needed at least 6.5V to reach 38KHz with the 10nF capacitor (lower capacitor value will allow a lower supply voltage), the 9V battery I was using at the time was running out and couldn’t supply enough power to reach 38KHz! Once hooked up to a clean 9V supply and tuned to 38KHz with the help of the mini DSO the jammer worked flawlessly. 😀
Some things to note, the transistor, 470R and 5R6 resistors and 1N4148 diodes form a constant current source for the IR LED of about 125mA, the transistor can get fairly warm. Using a supply voltage of 9V and LED Vf of 1.6V will result in a voltage drop of 6.8Vce across the transistor, at 125mA that comes to 850mW of heat (0.125A * 6.8Vce = 0.85W), which is actually above the rated 630mW for the 2N4401 which I used, so make sure to choose the right transistor.
[Schematic source (50 – 555 Projects on Talking Electronics)]