Audio Range FSK Modulator

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Cason

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Hi all,
I am trying to build a electronic circuit to transmit sine FSK signal from a TTL signal.
After reading some online article, I found several IC also can build the circuit, for example LM555, XR2206. But I found the mark frequency and the space frequency of those circuit are too high or too low. In my design, I am trying to use 14kHz and 17kHz to represent mark and space. Did anyone have any suggestions on which IC can I use?

Thanks a lot
Cason
 
The xr2206 is designed for that purpose.
When you say mark and space, are you referring to the mark/space between fsk modulation or the tones themselves?
I've worked with fsk recently for a rtty data logger.

Oh yes welcome to the forum.
 
4pyros said:
What is going to be controlling the FSK signal?
Click to expand...
I just want to transmit some data through the free space using the audible sound. So i try to send out the FSK signal through the speaker.

dr pepper said:
The xr2206 is designed for that purpose.
When you say mark and space, are you referring to the mark/space between fsk modulation or the tones themselves?
I've worked with fsk recently for a rtty data logger.

Oh yes welcome to the forum.
Click to expand...
Thanks, this is my first time to join the electronic project forum. Nice to meet you~
The mark/space i mentioned just like the logic represent 1 or 0. Since I want to convert the TTL signal to FSK, so i have two freq. to represent 1/0.
Moreover, the most worrier parts is that the IC XR2206 can give out a Sine waveform output ? and those two frequency (14kHz and 17kHz) can using this IC ?

Thanks
 
Yes you can do what you describe with the xr2206 at those frequencies, it has sine triangle and sqaure wave outputs.
The datasheet tells you how to perform fsk, and to calculate the components for the required freq's.
17khz in on the upper end of some peoples hearing range, and it would be expecting too much of some audio equipment to deal with.
 
OK, let try to use it ^^

4pyros said:
Here is one using the 555;
**broken link removed**
Click to expand...
It seem the 555 give out the square wave FSK, is there any way to convert to sine wave output ?
thx
 
What is going to be controlling the FSK signal?
is there any way to convert to sine wave output ?
Click to expand...
Yes like a D to A converter and a cap.
 
Hi All Again,
After the 15 days delivery , I got the IC and try to implement. And another problem appear:
According the datasheet, we have the formula f1=1/R1C , f2=1/R2C to represent two frequency.
I choice the C=1*10^-8f (103 cap), and the decide value of resistance.

But I found that the output is not stable in one frequency, for example: the frequency are 12.5kHz- 14kHz /15.2kHz-16.23kHz
I think the problem is the not stability of RC oscillator, but is there any way try to make the output frequency more stable ? (by changing the capacitor ?)

tHANKS
 
A ceramic capacitor changes its value. A 5% European film capacitor does not change. A 103 is probably an Oriental "greencap" that might not be stable.
 
A 32kHz watch crystal oscillator is very stable. If you divide by 2, you get 16kHz, and if you divide by 3 you get 11kHz. Perhaps, you can use this somehow.
 
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