FSK demodulator does not move my servo

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ayashifx55

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Hello guys,

I'm having a school project. I am making something remote controlled. I have a PWM (555 timer) going to FSK (to convert my square wave into sinewave) and transmtiting through VCO. Then i have PLL VCO as receiver which goes into my FSK Demodulator, it converts the sinewave (0-1) back to squarewave.

I tried controlling my servo with my PWM , works perfectly, precise reaction and movement. Tried directly PWM to FSK , FSK to FSK-DEMO .. servo goes crazy and does not react right. Moves back and forth repeatly where my original PWM , it only moves according to my PWM width is changed (by moving my pot)

Q: Is it because the FSK-demod is not producing the right current?

**broken link removed**
This picture shows my PWM (top) and my FSK Demodulated signal (bottom, does not react to servo, servo goes crazy....)

FSK i use XR 2206 and FSK DEMO i use XR 2211 , thank you very much for your help.
 
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because we can only use analog to transmit and receive , we are not allowed to use any receiver or transmitter IC. This is one of the ways i understand
to be able to control a servo from distance , PWM but you cannot transmit square wave.
 
Just key the carrier ON and OFF, it's how radio control always used to be, and what servos were designed for.
 
You cannot transmit a squarewave wirelessly, only sinewave or triangular wave can be transmitted.
THerefore, to transmit my PWM(Pulse width modulation) 0 & 1's ,i have to convert them into sinewaves which is what FSK does
FSK Demodulator converts my sinewave back into squarewave.

Each 0 and 1 is represented by a different frequency therefore possible archieving this conversion and transmission !
 

Your initial premise is incorrect, you certainly can transmit a 'square-wave' - simply key the carrier ON and OFF - you're adding extra layers of complexity for little reason.

A lot depends though what radio system you're using, ON/OFF carrier wave transmission is essentially an AM system, so you need an AM (or CW) receiver.

This is how radio control systems worked for decades, a simple AM ON/OFF system, and is what the servos were originally designed to be fed from.
 
ayashifx55 said:
You cannot transmit a squarewave wirelessly, only sinewave or triangular wave can be transmitted.
Click to expand...
Don't know why you say that. You can modulate a carrier with any shape of waveform, not just a sinewave or triangular wave. In this case you can think of it as 100% AM modulation of the carrier with a square-wave.

Of course the rise and fall times of the squarewave are limited by the bandwidth of the transmitter and receiver, but that's not a problem in this application.
 
Sorry for what i mentionned.

I also forgot to mention the only receiver i have learned is PLL (phase lock loop) i tried it and it does nto modulate square wave, unless you guys has better idea , by suggesting a circuit ?

It does not really help when im wrong and you guys only correct me in terms of knowledge only without any circuits name has to be practical if possible.
 
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I don't really understand what you mean by 'PLL receiver', there's not really any such thing - a PLL can be used as part of a receiver, in a number of ways, but they don't prevent CW modulation.

Perhaps you should post the circuits you're using?.
 
It is possible to capture a VCO signal with a PLL, maybe i mis-explained myself. I know PLL isnt a complete receiver but it does receive and then demodulates the frequency carrier so i can use that carried frequency.
 
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ayashifx55 said:
It is possible to capture a VCO signal with a PLL, maybe i mis-explained myself. I know PLL isnt a complete receiver but it does receive and then demodulates the frequency carrier so i can use that carried frequency.
Click to expand...

Nope, that's not what a PLL (phase-locked loop) does at all.

Why don't you try this: how about if you tell us what you're trying to do? I don't mean tell us what you've been telling us up to now: say what task you want to perform (control device X remotely from device Y or whatever). Also include any requirements for how you want/need to do this. Then maybe folks here can advise you on the best way to actually accomplish your task.

Just a thought ...
 
I was scared if i explained too much you guys would hate me sorry for not having so much details

I am trying to control from a short distance, two servos. My oscillators (PWM) controls precisely and perfectly my servo's (the width is perfect) but once i convert them into FSK and demodulate them back into squarewave, my servos just jumps all around.
 
If the PLL detector can't demodulate square-wave modulation then why not use a demodulator that can, such as a simple diode envelope detector?

As everyone has stated, using FSK to try to do square-wave modulation is overkill.
 
it's for a school project, i have about three weeks left. My progress reports were written based on the FSK's and FSK DEMOD's i have made (results and progress) so i guess it's too late to change lol.

If my servo jerks back and forth by itself, for example, it turns right 90 degrees then jerks back slowly to where it was, does this mean i need more current?

This is the FSK demodulator i am using :

**broken link removed**

This is the FSK modulator i am using :

**broken link removed**


Do you think its because the FSK demodulator does not provide enough current at the output therefore my servo is going crazy and not responding well to the PWM ? Thank you very much for your time =)
 
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ayashifx55 said:
I was scared if i explained too much you guys would hate me sorry for not having so much details
Click to expand...

OK, calm down, take a deep breath, etc. ...


OK, so we know 1) you want to control 2 servo motors remotely, and 2) you're using PWM to control them.

So what you want to do is transmit the PWM signal(s) to the servos, correct? Forget about FSK, PLL or anything else just for the moment.

If that's what you want to do, it can easily be done by a variety of methods. Let's make sure we're on the "same page" first, OK?
 
OK, so all you need is to use the PWM pulse train itself--forget FSK!--as a modulating signal. Simple AM would work fine. Lots of commercial solutions available, or you can build your own circuit, your choice.

Think of the PWM signal as the "music" you want to broadcast, and the receiver as the "radio" that will play that "music" to your servos ...
 
i am not allowed to use commercial solutions , everything must be analog , it is for a final collegial year project.
They are testing what i know .... therefore, thats why i used FSK / FSK DEMOD because i had access to those
circuits ....

PLL and VCO carrier are the only transmit & receive method we were taught about.
 
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