need of long range IR transmiter

[panadol]

thanks for the speedy reply,
the tsop im using is 38khz.
will it blow the LED at 1A-38khz pulse?or shud i make the hightime short and longer low(0) time so that the LED will not blow?(to maintain at lower duty ratio?)

i am using reflection technique to detect the IR on the receiver, should i go for narrow beam or wide beam IR?whish has better range?and what are the pro and cons?
thanks

 

[audioguru]

The datasheet for your IR LED should spec a max pulsed current rating and a minimum duty-cycle for it.

The TSOP receivers have an automatic gain control that reduces the gain during a continuous signal, because it thinks it is interference. Therefore the data must be received in bursts of from 10 to 140 data pulses then a gap time of at least 14 pulses between bursts for its gain to continue at max.

An LED makes a narrow beam by focussing it. Then its intensity is increased and its range will be far. But it might be difficult to point or reflect a very narrow beam that is invisible at the receiver, a beam with a wide angle would be easy but have less range.

 

[Nigel Goodwin]

thanks for the speedy reply,
the tsop im using is 38khz.
will it blow the LED at 1A-38khz pulse?or shud i make the hightime short and longer low(0) time so that the LED will not blow?(to maintain at lower duty ratio?)

Like Audioguru says, you don't run it at 38KHz continually, it's usually coded in some way, and the coding is designed to give plenty of rest time inbetween the 38KHz pulses. Check my IR PIC tutorial for details of the Sony SIRC's system.

 

[panadol]

From what compass1982 has posted
https://www.electro-tech-online.com/attachments/transmitter-png.10011/
The frequency of the 555 timer is actually 32.9khz (T=30.36us). and it is not anywhere near 38khz.(i used T=0.69(Ra+2Rb)C to calculate).
I did a simulation using multisim with the calculated values from the formula and happens that the simulation result is 20khz and not 38khz.
I am just wondering how to determine the values of Ra, Rb and C when the actual and the calculated is so far apart.
anyone can show me the values that u used to generate a 38khz frequency for TSOP1738?
thanks

 

[audioguru]

Are the values of the timing parts too high and too low for a 555, as shown in the circuit posted by compass1982? The resistors are nearly short circuits and the value of the capacitor is far too high. Look at the graph of recommended parts values in the datasheet.

Are the values of your parts 5%? Then the 38kHz could be anywhere from 34.2kHz to 41.8kHz if your numbers were as accurate as the calculation formula in the datasheet.

Is your power supply properly bypassed? A 555 draws current spikes of up to 400mA (!) when its powerful output switches that must come from somewhere.

Multisim doesn't seem to know if it is coming or going and makes many mistakes.

 

[philba]

I don't think those resistor values are good.

FWIW, LTSpice simulates it high - 44Khz. I suspect the model breaks down due to the low resistors. taking the resistors to 1K and 1.7K and the C to 10n (10000pf), it simulates a spot on frequency.

 

[panadol]

got it...i will try it out with the recommended values in the datasheet first..
thx...i used a 7805 to regulate the voltage for the 555

 

[v0xyzzz]

The datasheet for your IR LED should spec a max pulsed current rating and a minimum duty-cycle for it.

The TSOP receivers have an automatic gain control that reduces the gain during a continuous signal, because it thinks it is interference. Therefore the data must be received in bursts of from 10 to 140 data pulses then a gap time of at least 14 pulses between bursts for its gain to continue at max.

An LED makes a narrow beam by focussing it. Then its intensity is increased and its range will be far. But it might be difficult to point or reflect a very narrow beam that is invisible at the receiver, a beam with a wide angle would be easy but have less range.

can you explain the meaning of "Therefore the data must be received in bursts of from 10 to 140 data pulses then a gap time of at least 14 pulses between bursts for its gain to continue at max."? I'm getting confused of it... thanks for any help....

 

[audioguru]

can you explain the meaning of "Therefore the data must be received in bursts of from 10 to 140 data pulses then a gap time of at least 14 pulses between bursts for its gain to continue at max."?

The TSOP seres of IR receiver ICs are designed for remote control of TVs and other entertainment products. Data is sent in bursts of IR pulses and the automatic gain control in the receiver IC uses the breaks between bursts to know it is data and is not continuous interference. If it receives continuous pulses then it reduces its gain, thinking that the continuous pulses are interference from a compact fluorescent bulb or other item that continuously pulses IR at 38kHz.

The data burst consists of a start bit, the command code bits (volume up or down, channel number etc) then a device code (TV, DVD player, CD player etc). Then a pause between that burst of pulses before the burst of pulses is repeated again if the button is still held down.

 

[panadol]

i managed to get my timer to operate at 38khz already........thanks...will try out the TSOP receiver once i get it.
any comments about long range and wide range transmitter?any of it to recommend?My desired is about 20ft of transmission

 

[panadol]

ive tried my TSOP1738 receiver.
TSOP1738 gives me an increase of about 10cm...which is a total of 45 cm only.
I am using a high power transmitter operating at 100mA(its max rating) at 38khz.
i am wondering how can I boost the distance up to 20feet?Anyone can help me in this?i even tried boosting the transmitter to 200mA and the distance remains the same...
I wonder how does TV remote control boost its IR signals that it will be able to detect it even those its not aligned to line-of-sight, and with a long range?

i removed one of my TV remote and used its IR emitter,however it gives me the same detection range..

can anyone suggest me a long range circuit?thanks

 

[audioguru]

Panadol,
You forgot to attach the schematics of your IR transmitter and your IR receiver so we can see what you are talking about and if they are designed correctly.
Are you transmitting bursts of data?

You mentioned "reflection technique". Please explain.
I can point my TV's remote at the shiny white wall about 2m behind me at night and it controls my TV about 5m in front of me.

 

[panadol]

my circuit is fairly simple
i used a normal 555 timer circuit with R1=6900,R2=5100 and C=2nF to get it working at 37.88khz. I tried different currents for the emitter, 90~100mA, and also up to 200mA but the distance remain the same.
I am not sending a burst of data and i dun that.

all i need is just to sense an obstable 10 feet away. that is why i said i need a reflection technique which the total is 20 feet.(isit called duppler effect?).
My TV remote and sense more than 5m too,but i dun noe how to make my circuit to be a able to sense around 20 feet which is around 7-10m..... i wonder how those remote control works too...

 

[Nigel Goodwin]

Well you don't have a series resistor on the LED, so it's rather nasty to both the 555 and the LED!. To increase range you need to use a driver transistor to increase the power to the LED - it's usual to pulse than at about 1A or so, but ONLY with a very low duty cycle - this easily gives about 30-40 feet range.

 

[panadol]

ooh...means that i have to amplify the current from the pin3 of the 555 upto almost 1A?im not very good in transistor and current amplifying cicuit,thats why i avoid,using it...can suggest or show me any circuit?
if its like that, i will have to re-adjust my R1 and R2 values, is 10% duty ratio ok?at 38khz?but the max ratings of the transmitter is 100mA......just afraid it will blew up the LED....btw, what is the current supplied to tv remote controls(powered by only 3V, can it reach 1A?)?
thank you very much

 

[audioguru]

Your 555 circuit doesn't have a supply bypass capacitor to supply high current to the 555 and to the IR LED. Maybe that is why they didn't burn out without a current-limiting resistor.

If you don't send bursts of data like the datasheet says to do then the AGC in the TSOP reduces its gain. Then its range will be short.

Are you trying to sense a reflection from an object that is shiny and white or from a mirror that reflects perfectly? Then it will work.
If you are trying to sense anything else then you need a camera or something different.

 

[Nigel Goodwin]

ooh...means that i have to amplify the current from the pin3 of the 555 upto almost 1A?im not very good in transistor and current amplifying cicuit,thats why i avoid,using it...can suggest or show me any circuit?
if its like that, i will have to re-adjust my R1 and R2 values, is 10% duty ratio ok?at 38khz?but the max ratings of the transmitter is 100mA......just afraid it will blew up the LED....btw, what is the current supplied to tv remote controls(powered by only 3V, can it reach 1A?)?
thank you very much

Check my PIC tutorials, the IR hardware shows how to connect the IR receiver and the IR LED - you could use the same LED driver with your 555.

TV remotes commonly pulse at 1A or higher, they rely on a good sized electrolytic to provide the high current pulses, and short bursts of IR - with plenty of time for the capacitor to recharge in between them (my IR tutorial does the same).

Basically a TV remote sends coded pulses, then a completely blank period, then repeats again - this means the IR LED has time to cool down between data streams.

 

[panadol]

audioguru,
yes, i am trying to sense from a shiny surface whihc is 10 feet away.and my transmitter and receiver is placed at the same place.what is a bypass capacitor?and where to place it to supply high current?quite blur with that method to boost current
thank you very much

nigel goodwin,
i will try to pump it up to 1A and see whats the result, but i have to use a very short duty ratio right?what is the high voltage of RB1 in your tutorial?what is the alternative besides BC337?
sorry to give u guys so much trouble just becuase i suck at it...
i'll try doing it and let u guys know the result.thanks.
thnk you vry much too

 

[audioguru]

A bypass capacitor of about 100uF should be connected across the power supply to provide the high current for the 555 and for the IR LED.

Are you sending bursts of IR pulses?

 

[panadol]

hhmm..ok..but how high will the current be?i will test it out.later...
i am just sending a square wave which is tuned to 38khz, its that consider burst of pulses?and my current duty ratio is aobut 50%.
my whole motive is just to sense something infront 10feet away, hence i dont need any modulation technique for my microcontroller to dingtinguish between different signals. all i want is transmitter send detect an obstacle 10 feet away, and then reflect back to the recevier which is at the same plane of the transmitter..hope i made it clear

i am curious how remote control are tuned.the IR emitter in remote control are just ordinary ones,but how they made it that it can be sense at all directions even not pointing directly to the tv?(if im not wrong, IR in remote contorl is narrowbeam...)
THANK YOU SO MUCH!!ALL OF YOU!