# Obtaining different signals from a single square wave

#### Surtur

Joined Nov 22, 2015
7
In our term project, we are asked to design a car which can move in 5 directions, forward-left-right-clockwise-c.clockwise, and for those movements we are restricted to use only 3 different sinusoidal signals which must be obtained in our design. so I considered that instead of creating 3 different sinusodial oscillator circuits, I will construct a single square wave generator and then, using 3 different band-pass filters with high quality factors I will obtain the desired signals to control the motors in car. What do you think about this idea? Is this efficient or anyone tried it, would it work? If youre interested, I can post our term project specifications' document. Thanks already

#### crutschow

Joined Mar 14, 2008
34,700
A square-wave contains only harmonics of the fundamental so those are the only signals you can extract from the square wave.
If you want three independent frequencies (not related by harmonics) then you need three oscillators.
Three separate oscillator circuits would likely take no more circuitry then your high Q filters.

#### Surtur

Joined Nov 22, 2015
7
A square-wave contains only harmonics of the fundamental so those are the only signals you can extract from the square wave.
If you want three independent frequencies (not related by harmonics) then you need three oscillators.
Three separate oscillator circuits would likely take no more circuitry then your high Q filters.
Oh yes! I totally forgot about harmonics. Then I ll construct 3 different oscillators.

#### MrAl

Joined Jun 17, 2014
11,583
Hi,

With a 1kHz square wave you could extract 1kHz, 3kHz, and 5kHz. Not that bad, and any drift will appear in all three frequencies.
With three oscillators you can set the frequency to whatever you want it to be, but each one will drift as it will.
Probably the wider the frequency spacing the easier it will be to detect each one.

#### Surtur

Joined Nov 22, 2015
7
Hi,

With a 1kHz square wave you could extract 1kHz, 3kHz, and 5kHz. Not that bad, and any drift will appear in all three frequencies.
With three oscillators you can set the frequency to whatever you want it to be, but each one will drift as it will.
Probably the wider the frequency spacing the easier it will be to detect each one.
well you are right but the restriction of frequencies is dependent on our student numbers so they are varying with a range of 40kHz range. (10k+.. - 30k+... - 50k+....) I think they can be easily detected.

#### MrAl

Joined Jun 17, 2014
11,583
well you are right but the restriction of frequencies is dependent on our student numbers so they are varying with a range of 40kHz range. (10k+.. - 30k+... - 50k+....) I think they can be easily detected.
Hi,

Oh ok i did not know you already had a restriction on the frequencies you were allowed to use. That changes things a little then.
Still sounds like it can be done though.

#### recklessrog

Joined May 23, 2013
985
Early multi-channel Radio controlled models used different modulation frequencies to vibrate resonant reeds to operate actuators. But why not use PWM with as many channels as you like. simple encoder decoder. Google Digi trio radio control from the late 60's for an in depth insight into early digital radio control. You can still download the full construction series. (I built one at the time for my R/c boats)

#### Surtur

Joined Nov 22, 2015
7
Early multi-channel Radio controlled models used different modulation frequencies to vibrate resonant reeds to operate actuators. But why not use PWM with as many channels as you like. simple encoder decoder. Google Digi trio radio control from the late 60's for an in depth insight into early digital radio control. You can still download the full construction series. (I built one at the time for my R/c boats)
To be honest I didn't really understand your method but as far as I got, we are allowed to use sinusoidal waves to transmit input. I shall use PWM to control speed by the way

#### recklessrog

Joined May 23, 2013
985
Whether you are using radio or infra red or similar to transmit with, why not modulate the carrier frequency with 3 different frequencies spaced far enough apart for 3 bandpass filters to separate in the receiver.

#### SLK001

Joined Nov 29, 2011
1,549
In our term project, we are asked to design a car which can move in 5 directions, forward-left-right-clockwise-c.clockwise, and for those movements we are restricted to use only 3 different sinusoidal signals which must be obtained in our design. so I considered that instead of creating 3 different sinusodial oscillator circuits, I will construct a single square wave generator and then, using 3 different band-pass filters with high quality factors I will obtain the desired signals to control the motors in car. What do you think about this idea? Is this efficient or anyone tried it, would it work? If youre interested, I can post our term project specifications' document. Thanks already
With a single square wave, you have one degree of freedom. That means you can only control one thing. With two frequencies, you have 4 degrees of freedom - with three, you have 9 degrees of freedom.

#### bertus

Joined Apr 5, 2008
22,290
Hello,

@SLK001 , When counting binary, 1 signal will give 1 choice, 2 signals 4 choices and 3 signals 8 (and not 9) choices.

Likely the when no signal is present, that will be the rest position, so leaving 3 and 7 action positions.

Bertus

#### SLK001

Joined Nov 29, 2011
1,549
Hello,

@SLK001 , When counting binary, 1 signal will give 1 choice, 2 signals 4 choices and 3 signals 8 (and not 9) choices.
Oops, you're right... it is 2^3. Brain fart.