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11 December 2010
Author: Giorgos Lazaridis
Long Range (10mt) IR Beam Break Detector

Shortly after i published my IR Short Distance Beam Cut Detector circuit, i began receiving emails and comments, asking how to increase the range. As a matter of fact, that circuit was designed for a very specific application: it had to be precise and sensitive enough, because i wanted to use it for the straw separator of my coffee maker machine. Because people keep asking me for a long-range IR beam break detector, i made this circuit which has a range of nearly 10 meters (33 feet), with only a single high power LED, using no lenses.

The Circuit - The Transmitter

Here is how the transmitter works. As you see, i have use one 556 timer, which contains 2x555 timers. You can use a 556 as well, or you can choose to use 2 individual 555 timers check the 555 timer theory). It will operate without any problems. The first part of the 556 (IC1A), generates pulses of about 1.5 msec duration, with 30 mSec interval (signal frequency is about 32 Hz). The second part, generates the carrier signal which is 38 KHz. The transistor Q1 switches the carrier signal (38 KHz) on and off, according to the previous (32Hz) signal. In simple words, the IR LED receiver a pulse train of 38 KHz, 32 times per second (32 Hz), each time for 1.5mSec. This is the modulated signal. To further understand this circuit, i got some screenshots from the oscilloscope (as always, click to enlarge images):

 This is the 38KHz carrier signal - the correct frequency for my IR receiver These are the modulation pulses (32Hz) - will be inverted after the transistor Each pulse has 1.5 to 1.6 mSec duration.

These two signal are then modulated (and inverted) with the transistor Q1, and here is what arrives at the IR LED:

 These are the inverted and modulated pulses. On every positive duration of the pulse, the carrier wave (38KHz) is transmitted This is only one pulse on the screen of the oscilloscope (zoomed). The 38 KHz signal can now be seen clearly

So, the IR transmits 38KHz signal, with 1.5 to 1.6 mSec duration and 30mSec interval. This is what the receiver must receive.

Bill Of Materials - Transmitter
 Resistors R1 Resistor 47 KOhm 1/4 Watt 5% Carbon Film R2 Resistor 2.2 KOhm 1/4 Watt 5% Carbon Film R3 Resistor 6.8 KOhm 1/4 Watt 5% Carbon Film R4 Resistor 22 KOhm 1/4 Watt 5% Carbon Film R5 Resistor 220 Ohm 1/4 Watt 5% Carbon Film R6 Resistor 1 KOhm 1/4 Watt 5% Carbon Film Capacitors C1 Ceramic Capacitor 680 pF 50 Volts C2-3 Electrolytic Capacitor 1 uF 50 Volts Transistors T1 2N2907 General purpose amplifier and switching transistor Semiconductors LED1 High output IR LED Integrated Circuits IC1 556 Dual 555 Timer

What is this "High output IR LED"

I tried several cheap IR LEDs - No good

I mention this IR LED as high output, but i do not give any part value. Frankly speaking, i do not know one. I tried several LEDs that i got from different suppliers -including ebay-. One word: Do NOT shop this from ebay! No matter what the seller says, just, don't. All the LEDs i tried had a range of 2(ebay) to 4(others) meters. So, i did some more research and i found that there are actually "high output IR LEDs" such as the 510E850C from Hebei I.T. (Shanghai). Although i have not tried this LED, i suppose that this is one good IR LED for remote controls, or maybe it can be TOO MUCH (100 mWatts !!!!!!). In any case, if someone tests or knows another IR LED suitable for remote controls, then please let me know.

What i did for my remote? Well, it just happened to have an old remote control in my museum. I hacked it and removed the IR LED from inside. Luckily, it did work perfectly. With this LED, i managed to get 10 meters range (or maybe more)! What you need to have in mind, is that, unlike normal LEDs, these LEDs have usually a low forward voltage drop. My LED required 1.5 volts (that's why i chose a 220 Ohms resistor). In case you select a different LED, be sure you change the R5 accordingly.

 My old remote control from my museum Hack hack hack - Chop chop chop Easy to remove an LED from a single side PCB Soldered 2 wires and is ready to be used!

Go to the next page to see the receiver circuit.

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