[SOLVED] 38Khz transsmitter circuit need help here

[ericyeoh]

555 38khz

any one can help me for this circuit below?
is that any problem with this circuit in the link?
can anyone tell me?
**broken link removed**

the circuit never mention what type of IR LED be use, so i just simply buy and use it, anyway is it possible the problem of transmit?

I saw some forum dicuss by putting 2 IR LED at the output (pin3) of 555
what for ??

 

[wp100]

38 khz oscillator

Hi,

Invalid link ...?

 

[vsmGuy]

38khz emitter design

Oh please.. search the forums for an ready-to-go answer!

 

[ericyeoh]

ir transmitter 38khz and receiver 38 khz circuit

**broken link removed**

 

[pranam77]

38k hz infra red

any one can help me for this circuit below?
is that any problem with this circuit in the link? **broken link removed**
can anyone tell me? the circuit never mention what type of IR LED be use, so i just simply buy and use it, anyway is it possible the problem of transmit?
I saw some forum dicuss by putting 2 IR LED at the output (pin3) of 555
what for ??

I see no problem with the circuit. It should work fine. You may use any 5mm IR led available in open market. If you are still not satisfied, use any one from a old remote control handset. Two IR led's are mormally used for wide coverage and more range. Good luck.

 

[banjo]

38khz filter circuit

While the circuit will work for its intended purposes, please be aware of some undesirable side-effects. If you modify the circuit to detect people walking through the doorway of your home, you will probably be confused as to why your TV remote stops working.

This simple circuit runs on the same modulation frequency as common IR remote controls. This allowed the designer to use an easy to get IR detector. However, since it puts out a constant 38KHZ signal, it will swamp out the IR receiver in your remote control equipment and cause problems.

Used outside, this constant 38KHZ is not a problem. Used indoors, be careful that is does not interfere with remote controls. IR light bounces off walls and ceilings, so direct line of sight is not required.

 

[ericyeoh]

remote control 38khz

oh ic , i just use this circuit in my project, so there are ntg relate to the house equidment, anyway tq for sharing this info, this might be new thing to all the people who watch this acticles.

i think it might be my IR emitter problem, i'm going to change the other type and compare the result , thx ya!

 

[Audioguru]

38khz tv remote circuit

It is an extremely poorly designed circuit (like most circuits from that site).

The IR receiver IC has automatic-gain-control that reduces its gain when it receives continuous 38kHz IR from compact fluorescent light bulbs or from the circuit's 555 oscillator.
The datasheet for the IR receiver shows how the 38kHz should be chopped into bursts so that the gain remains high. When it is used in a remote control circuit then the data creates bursts of 38kHz.

The current from the 555 to the IR LED is rather low.

 

[ericyeoh]

stable 38 khz 555

The current from the 555 to the IR LED is rather low

actually what u mean by this?

if the output currect form 555 IR LED is low...is it got effect on the transmittion?

pls briefly explain about this tq

 

[FvM]

38-khz ir led circuit 555

If you consider a dependency of IR LED's optical output power on input current, what kind of relation do you expect?

You may want to consult an IR LED datasheet for clarity.

 

[Audioguru]

38-khz ir led circuit 555 oscillator

Remote controls for home electronics blast 1A current pulses into their IR LEDs for very good range.
This circuit has a 555 operating from 6V so its output high voltage is +3.5V. The IR LED has a forward voltage drop of about 1.3V which leaves only 2.2V across the current-limiting resistor. Ohm's Law calculates the current at only 100mA.

Of course the IR LED must be built to survive 1A (or an array of lower current LEDs) if you want good range. Also a better circuit that the old 555 is needed for 1A current pulses.

As mentioned before, the IR must consist of bursts of 38kHz with pauses in between as shown on the datasheet for the IR receiver IC.

 

[ericyeoh]

filter 38khz ic

Wow! if 0.1A and 1A have different result so much
Better to build an 38khz oscillator circuit have the current where the IR LED can radiate at 1A.
can it goes better?

 

[ericyeoh]

38 khz oscillator circuit with transistors

but by looking the circuit it say it is 38khz,
from the formula f =1.4/(R1 + 2R2) × C1
substitude all the value inside the frequency is about 34khz only what?

if i change the R2 = 18k , the frequency will close to 38khz!

anyone can give opinion?

 

[betwixt]

38khz ir remote ic

You might find these two links about IR interesting:

http://www.atv-projects.com/IR_Remote_Control.html

which explains about the carrier and why it is needed and gives some insight into the coding methods used by IR devices.

and

http://www.atv-projects.com/SAP.html
(follow the link to part 1 of the SAP schematic)

which shows a microprocessor driving an IR LED via a 555 to operate a VCR over a 50 mile (80Km) range. There are notes elsewhere in the web pages about different types of 555 and why some will work and others not.

Brian.

 

[FvM]

38khz ir modulation 555

a microprocessor driving an IR LED via a 555 to operate a VCR over a 50 mile (80Km) range

Can you kindly point me to the exact place, where to find this result (I'm just interested to understand the involved optical effort). Unfortunately, I missed it in the said ATV IR remote control link.

There are notes elsewhere in the web pages about different types of 555 and why some will work and others not.

A single BJT transistor allows to adjust the current drive level according to your needs, without worrying about 555 specifications.

 

[betwixt]

38 khz circuit

Sorry, I misled you, the IR LED is to control a VCR (now replaced by a DVD recorder)
which is co-located with the box described. The control that works over long distance is by radio at 1.249GHz which is decoded and then used to pulse the 555 carrier stream. Someone transmitting audio and video 80Km away can request that they are recorded then played back so they can 'see' themselves from a distance when normally their transmitter would swamp their receiver. They transmit the record command, send pictures, send the rewind and playback commands then switch their transmitter off to watch the signal from the other end.

You can see it in action at www.batc.tv, click on 'ATV repeaters' then 'GB3ZZ' then 'view stream'.

Agreed that transistor drivers are the normal solution but a good bipolar 555 can sink/source 200mA which is more than adequate for medium distance IR LEDs.

Brian.

 

[ericyeoh]

38khz transsmitter circuit need help

i still not understand!

the question now is if i change the 20k resistor to 18k any effect on the transmmiter section?

and the supply voltage into the transmitter section is 6V if i increase to 9V can the output voltage(pin3) also increase?

 

[FvM]

38khz oscilloscope

You may want to consult a 555 datasheet to view the details yourself. You get a nominal frequency of 35.1 kHz with 20k and of 38.9 kHz with 18k resistor.

The output voltage is basically increasing with higher supply. But unfortunately, no minimum high output voltage is specified above 100 mA load current, only a typical output at 200 mA. As 555 has no specified current limiting or short circuit protection, you're also able to damage the chip.

 

[betwixt]

increase infared range circuit

Perhaps the query is about "why that frequency" rather than "why more current".

The IR stream is not just like Morse code by LED, the light isn't just turned on and off to send the 1s and 0s of data. If you did that there would be horrible problems from other sources of infra-red light causing interference.

To make it easier to pick the data out of the background noise, the LED current is pulsed at about 38KHz. The data is now either 'off' or 'pulsed' rather than 'off' and 'on'.

The reason: it is easy to filter one particular frequency out of the background signal. Instead of the receiver seeing a whole mess of signals, the filter can eliminate anything that doesn't look like it comes from the remote control. Filtering at 38KHz is easy to do and several ICs are made specially for the job. The reason 38KHz (or somewhere near) is chosen is a compromise, if the frequency is made higher, it becomes more difficult to generate the high current LED pulses, if it is made lower, you don't get as many pulses per '1' in the data stream so it becomes more ambiguous to decode.

You need your pulse stream from the 555 to be close in frequency to the filter in the receiver to maximize the detection range. As you frequency falls further away from the center of the filter mask, less of it reaches the circuit that detects its presence.

The 555 frequency is set by the RC network on its trigger and discharge pins so if you change those values you make the IR pulses change in frequency. The values should be set to match the receiver filter frequency. Sadly, the 555 is not very frequency stable as you change its supply voltage so this will also influence the frequency you get from it.

Brian

 

[Audioguru]

555 +38khz

Instead of using that old circuit that works poorly, why not use a modern circuit that works well?