Instructables

in what way we can convert dc voltage from battery into pulsating ac signal?

actually i am a beginner in doing mini projects. my projects is to increase the range of ir rays emitted by ir transmitter and i have  heard that it can  be done if we give ac signal as input than dc signal 

You can't increase the MEAN power, but you CAN increase the peak power, and therefore brightness, by PULSING the LED, but keeping the mean current below the rated current of the LED.

So if, for example, you have an LED that can take 20mA DC, and you want to run it 50 x brighter, you can pulse it for 1A, but only for 20msec in every second.
sandiri (author)  steveastrouk2 years ago
so is it essential to construct an amplifier circuit
Yes. What you want to make is a pulse generator, driving your LED, and it needs to be capable of driving a lot of current through the LED quickly.
bwrussell2 years ago
How much range are you looking for? You could switch to an ultrasonic transducer and receiver. They're cheap and interface with most microcontrollers.
sandiri (author)  bwrussell2 years ago
sir will you help me out by suggesting an alternate for microcontroller and transducer
Looks like their are others here that know how to make pulse drivers, I can only make suggestions based on my experiance.
sandiri (author)  bwrussell2 years ago
since ours is a mini project range is not much (it's about 50 cm)
sir do far i am not exposed to microcontrollers and receivers.so would you please suggest me how to construct an oscillator
Driving the transmitting LED with an AC signal is part of the trick.

The remainder of the trick lies in the receiver, i.e. in building a receiver circuit that can amplify and detect an AC light signal that is very faint. 

Also it helps when the modulated light signal is in frequency range different from other light sources in the room, which are essentially noise.  Probably the worst of this noise from other light sources is going to present at DC (f = 0 Hz), and also there might be some bad noise at 120 Hz too, due to electric lights that flicker at twice the mains frequency. 

For some reason most IR remote control (like for TVs, DVD players, etc) the IR light emitted by these is modulated at around 40 KHz (40 000 Hz).

The reason I mention IR remote controls, is because the actual IR receiver for these is a part that is cheap and relatively easy to find.  It is an IC with 3 pins and a little black (IR transparent) plastic bubble that houses the actual phototransistor. Two of these pins are for input power, +5V and ground, and the third pin, Vout, is a logic type output. It's high (+5V) most of the time, but goes low (0V) when it detects incoming light modulated at 40 KHz.

Some pictures IR receiver modules:
http://www.google.com/search?hl=en&tbm=isch&q=ir+receiver+module

So that is one way to solve the IR receiver problem: to just get one of those little modules.  Of course doing that means you will need a IR transmitter that flickers (turns on and off) at a frequency close to 40 KHz.

You could build that 40 KHz IR transmitter using a 555 timer chip, or whatever kind of oscillator you like.  However, if you are new to electronics,the 555 would probably be a good choice, since the 555 is pretty easy to use, and there exist many, many,  tutorials out there on how to use it.

If you want to build the transmitter and the receiver both, running at a frequency of your choice, I've think I've got some ideas for that too. However, I think just building the transmitter side, and using the premade 40 KHz module as a receiver, would be a good place to start.

Actually you can probably find an already made transmitter too, if you'd be willing to use an old TV remote with one button held down, which would be  cludgy, but it would probably work.

rickharris2 years ago
Put more IR LEDs in the package and invest in a lens for them remember your only going to get line of sight + reflections.
If you want a longer range on the IR transmitter then figure out how much power the IR LED can handle then take it to its max if the circuit isn't already pushing it to that point. Otherwise you'll just have to buy a more powerful IR LED.

An AC signal is only going to flash the LED it won't make it brighter and allow the light waves to travel further.
sandiri (author)  mpilchfamily2 years ago
sir actually my project is obstacle detection using ir transmitter and receiver so what would be the another alternate solution will it be attained using oscillator circuit...i know very little about it. i am very much grateful to you sir in advance