I moved before completing this and don't have any need for an IR Repeater at the moment. Therefore this project is on hold until I can get an oscilloscope or at least find a need for an IR Repeater again.
AT&T wanted to charge me $60 to have a guy come out and run some cable so I could have TV in my bedroom. Being a fresh (poor) college grad I told them I could do it myself, I just needed the cable box, but they continually dodged the question. They said that I could run a cable to the TV in the bedroom and then both TVs would be showing the same thing. Since the cable actually comes in on the phone line I was able to run a coax out of the cable box, into the wall, and then out of the wall to the bedroom TV. Now we can watch cable in the bedroom, but the remote doesn't reach the cable box because there are too many corners between the bedroom and living room. The solution here is obviously an IR repeater. A fairly simple battery powered circuit that will receive the remote signal in the bedroom and output a duplicate signal to the cable box in the living room.
I started out as I usually do with these projects by searching Google. I found several examples of other IR repeaters people have built, but this IR Remote Extender by Michail Papadimitriou was the best by far. It explains in detail how everything works including the IR signal modulation. I designed my circuit based on this example, making a few changes based on the parts that I had.
Now I have to build the circuit and do some testing. Soon I'll be able to control the cable box from the bedroom.
I've built the circuit, but it doesn't seem to be working right. It looks like it may be working with my Walmart surround sound, but not with the cable box or TV. The indicator LED blinks when an IR signal is received and by using a digital camera I can see that the IR LED does the same. There may be a number of things causing the circuit not to function properly, but without the proper tools it's hard to determine the exact problems. Here is a list of possible causes.
- IR wavelength: From Wikipedia I see that most IR systems use a wavelength around 930nm, 950nm, or 870nm. A couple of the IR LEDs that I got didn't have any specifications with them other than a typical current level of 50mA. One that I picked up at Radioshack list a wavelength of 940nm, but it doesn't appear to be working either.
- 555 Modulation: I'm using a 555 Timer to attempt re-modulating the signal at 38KHz. However, without an oscilloscope I have no way to compare the output signal to the input one. I've attempted to get as close to 38KHz as I can by using a potentiometer as part of the timer circuit, but without a way to measure exact capacitance it is impossible for me to calculate the exact resistance needed to achieve this.