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Topic: how 2 set the frequency?? (Read 1 time) previous topic - next topic

gobind

i m tryin 2 make a remote that vl work an air conditioner. i dont have the true remote. kindly suggest an idea 2 desgin a remote.So my qustn is what should b the frequency of the ir led???
(AC-VOLTS)

AWOL

#1
Feb 25, 2011, 07:45 pm Last Edit: Feb 25, 2011, 07:47 pm by AWOL Reason: 1
Quote
i m tryin 2 make a remote that vl work an air conditioner

It's OK, this isn't SMS - there's a 9500 character "limit" - you don't need to abbreviate.

What does "vl" mean? "very likely"?

What is the modulation frequency of the existing remote?
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johnwasser


So my qustn is what should b the frequency of the ir led???


It's usually not just a matter of frequency.  The IR carrier signal is usually 35 to 40 KHz but that frequency isn't very critical.  The critical part is the sequence of pulses.  Typically the remote will send a device address and a command.  That is how a remote can turn on a TV without also turning on the VCR, DVD, or cable box in the same room.

If you don't find the control signal documented somewhere and you don't have the original remote you will have to find a universal remote that can be programmed to control the A/C.  Then you can sample the signal and emulate it in the Arduino.
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Grumpy_Mike

I would agree with all that last post except:-
Quote
The IR carrier signal is usually 35 to 40 KHz but that frequency isn't very critical.

In fact the normal modulation frequencies are between 30 to 40KHz in steps of 2KHz, and it matters tremendously that you get the right one. The receivers are designed to block out IR that is not of the right frequency.
If you haven't got the original remote then maybe you can look at the chips in the receive circuitry.

gobind

Hi friends,
For a duplicate remote i just wanna know is it necessary to demodulate and then modulate the ir waves from the orginal remote, to reproduce the same ir waves? What can i do for it? To produce the same signal (eg .ON/OFF signal of a tv remote) what am i supposed to take care of?
Gobind Gopal

tempmj

You will need to know the frequency and the pulses of the remote.

For example, for a Scientific Atlanta Set Top Box, if you want to hit power, it's the following (where off is no IR output, and on is IR modulated at 56khz)

on - 3.36ms
off - 3.36ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms
on - .84ms
off - .84ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms
on - .84ms
off - .84ms
on - .84ms
off - .84ms
on - .84ms
off - .84ms
on - .84ms
off - .84ms
on - .84ms
off - .84ms
on - .84ms
off - 2.52ms
on - .84ms
off - .84ms
on - .84ms
off - .84ms
on - .84ms
off - .84ms
on - .84ms
off - .84ms
on - .84ms
off - .84ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms
on - .84ms
off - 2.52ms


without that exact timing, the scientific atlanta set top box won't turn on/off by IR.
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gobind

thank you for your reply.
Will i get that frequency and pulse of a remote with a simple ir detector (photodiode) and connecting to my micro-controller? Will the Serial Monitor help me in getting the pulses? If so what should be the program to get it?
Regards
Gobind

Simpson_Jr

I'm no expert, but i guess you could use the http://arduino.cc/en/Reference/PulseIn-function to detect the length of pulses of the original transmitter using an photodiode.

gobind

Will the circuit shown below do the receiving and show its output in the serial monitor to get the exact timings?

Can anybody give some tips on programming to get the timings of the receiving signals?

Grumpy_Mike

Quote
Will the circuit shown below do the receiving and show its output in the serial monitor to get the exact timings?

No, the filter on the output will ensure that you don't get any changes more rapid than 320mS.
You need two things:-
1) the modulation frequency
2) the period of the modulated pulses
Remove that capacitor to get signal 1
Replace that capacitor with a smaller one for signal 2

However you are much better off simply looking at the signal on the output of the detector with an oscilloscope. If you haven't got one then use your arduino as one, there are plenty of examples of doing this on the net.

gobind

I tried connecting to the oscilloscope with this circuit but its not working. I am a beginner so i wasn't able to understand the problem of this circuit.
Your explanation will be appreciated.
Thank you.

Grumpy_Mike

Quote
I tried connecting to the oscilloscope with this circuit but its not working

The oscilloscope or the circuit?

If you get nothing on the output of the detector when you are firing a remote control into it then you have one or more things wrong:-
1) The remote is not working. Try looking at the output using a digital camera, you should be able to see the light.
2) Your detector is broken.
3) You have wired it up wrong.

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