I liked the tvbgone kit from Ladyada the first time i saw it but i never had the time to build it, until a week ago. But than i decided to build a more powerful one that could turn off TV’s from even greater distance. I came up with a design that consists of 48 IR LED’s and a ATmega8 that will send the signals to the LED’s.
the led board
Unfortunately i wasn’t paying attention on a small paragraph from Ladyada that was saying “Use 940nm IR LEDs.” so without knowing i bought 860nm IR LED’s (L53SF6C from Kingbright). I did not knew at that time that this is going to affect the distance at which the device works. Why L53SF6C ? they seemed nice because at 50 mA they have typical 100 mW/sr so allot more power than the F3(940 nm) series which had 30 mW/sr at 50 mA.
I arranged the LED’s in 4 rows of 12 pieces and the resistors fit quite nicely between the LED’s. I used four BD139 NPN transistors to drive the rows. It took me hours to drill and then solder this board(48 LED’s and 48 resistors mean 192 holes plus the other parts)
the controller board
The controller board contains an ATmega8 chosen because of it’s 8k memory needed to store all the codes, an 8 MHz crystal, an LED, a tact switch and some resistors and capacitors. I designed the board so that it can also be used for other projects.
It took me some time to adjust the code from tiny85 to ATmega8, getting the timers right was tricky but i managed to get it done. Also i had to delete a couple of codes to fit it in the 8k’s of the ATmega8.
The whole project is powered from a Nokia BL-5B battery which was ugly fitted onto a peace of PCB 🙂 . I can’t seem to find a decent socket to hold such a battery. I’ve run the circuit for over a week every day and the battery is keeping up, and when it gets discharged I’ll simply charge it inside of an old nokia phone.
Well as you can imagine the first thing i did was to test it on the TV’s in my place, it worked perfectly. Next i wanted to test it on a larger scale so i took the device onto a nearby supermarket were they have a bunch of Tv’s onto a wall. I had to conceal the device somehow so they don’t kick me out of the store 🙂 so i placed the device inside a CD case. I don’t know how much the case is obstructing the signal, but it was turning off TV’s from a distance of 20 meters.
Probably choosing the right wavelength LED’s would double the distance, and by using a clear case the distance would double again, but that’s just a guess.
The boards were designed in Eagle and fabricated by me using the photo etching technique.
I’m planing to build a newer version, in fact i already sent the files for PCB fabricating. This new version will use only 4 LED’s just like the original design, and will be smaller thus easier to conceal and it will also use ATmega8 for the controller. I’ll post pictures as soon as i get it done.
some more pictures..