Hello Everyone,
I am doing little project, generating audio signal @600Hz or @2400Hz .
Wave form of the signal must be in sine wave ramp up and ramp down when circuit switchd on and off. I have to show these signals end of the day(image attached ). I tried with basic RC phaseshift oscillator to do this , whenever I swithed on it ramping up slowly but not its not working properly(i want sine waves ramp down slowly) when it switched off.
Speaker(4 or 8 ohm @less that 5Watt) is working fine with different circuits(with 555 timer and LM386 Audio power opamp), still I haven't consider those circuits for my project because I need the sine wave signals ramp up and ramp down(nothig but amplitude changes when it on/off.).
Can anyone guide me in this issue. Thank you all in advance.

 

Are you determined to have a "linear" ramp up and ramp down, or would an exponetial "attack" and "decay" work just as well for your purposes?

 

Thank you for quick reply.. I didn't get it.. what you mean...sorry.
But breifly I am trying to combine two different frequrncies (approx~~ 50Hz(square wave) modulating and 600Hz sine wave carries) My sine wave amplitude must vary according to square wave.

Please ignore this message if it confuses you.

 

Now it's my turn. I don't understand how you plan to combine the two signals. What I was talking about was how you want to turn on and turn off the output of a sinewave oscillator. Now it seems you are trying to do something else.

 

you need to be clearer about your specs. ramp up and ramp down are like a triangle wave ( and the way you phrased it I assumed you meant in frequency ) Your drawing makes it look like amplitued modulation instead, with only 2 levels, on and off.

It seems a waste of time to tell you how to do it untill we know what you want to do. What frequency and amplitude is the square wave, how is it generated.

Would be nice to know the

 

Thank you for all those comments. I agree, these above two posts make confusion that's because my lack of presentation and lack of experince in forum communication. I try to learn these as soon as possible, even it makes me nerves to post querris.
Here more clear(I dooubted) for get about all I mentioned in previous posts. This RC phase shift oscillator @ frequency 1 KHz (1ms),generate sine waves and clock attached to this @50Hz it switches on /off every 20ms. (In untitled.JPg attached file)The output in oscilloscope, showing it ramping up slowly with proper sine waves, but when clock is off ramping down but not in the form of sine wave. Can you suggest me how can I achieve this. With lack of knowledge in this subject, I am unable to find the solution. Moreover I haven’t designed this circuit, it's also one of the reason. Please educate me in this.

Finally As I said in previous posts, end of the day I have to show as shown(window.png attached file) below.

All I am trying to ask you , can I generate these amplitude variable sine wave using clock operated(like on/off switch). Right now I am half way through(!!!!!?). Or is there any better way through. I am afraid it is not like a Amplitude modulation because no input signal(only on/off switch). More over it is using only DC voltage. Please let know if you're still in confusion........!!!
Thank you each every person who is viewing this post.
Files attached.

 

you need to be clearer about your specs. ramp up and ramp down are like a triangle wave ( and the way you phrased it I assumed you meant in frequency ) Your drawing makes it look like amplitued modulation instead, with only 2 levels, on and off.

It seems a waste of time to tell you how to do it untill we know what you want to do. What frequency and amplitude is the square wave, how is it generated.

Would be nice to know the

Hi russ_hensel , I mentioned the square wave to easy to understand(as REF) . I mean like a envelope signal (I cosidered around tr&tf= 16ms(rise time and fall time) td=128ms) for clarification. by using this signal as input or( any input signal like or switch) my actual ckt must produce sine waves(~~1KHz) with varying amplitude. Right now I used just phase shift oscillator to produce these signals using clock. I attaced signals and ckt diagram in my previous post.
And about amplitude I have no limitations but as a starte I am using 5V amplitude, suggest me If I missed anything or any wrong side.
I am trying to learn few things in this project developement. If anyone better ideas please let me know.
Thakyou for all your contribution.

 

Now it's my turn. I don't understand how you plan to combine the two signals. What I was talking about was how you want to turn on and turn off the output of a sinewave oscillator. Now it seems you are trying to do something else.

Hi papabravo,
I confused you, sorry about that... those are my ideas, I am asking you all few ideas in this project developement. I have no limitations in this project , regading specifications. I mean input might be clock signal or on/off switch.
I mentioned specs in my previous posts. Let me know If yourn't still clear.

 

Your phase-shift oscillator circuit ramps up the level of its sine-wave because its gain is too low. It has nothing like an attenuator to slowly ramp down its sine-wave.
It is a simple distorted oscillator.

Usually a Jfet is used as a linear attenuator to ramp up and ramp down a tone level.
The Jfet can keep the distortion low by limiting the max output level before the transistor clips.

Many years ago I used a Jfet to ramp up and down background music on a high quality huge intercom system so that the music faded when an intercom call was received and ramped up the music when the call ended.

 

I am still not quite sure what you are tryinng to accomplish, but I think what you want is an amplitude modulated sine wave. If so one way to do it is to let the ossc. run all the time and then modulate it. You would also need a second signal for the modulation, which could have any shape you want. For modulation you need either a voltage controlled ( in amplitue ) amplifier ( or for just on off, an enable disable pin ) amplifier. More generally a 3 or 4 quadrant amplifier ( there are ic's for this ).

However you frequencies are so low that you could also accomplish all of this with a microcontroller and dac programmed for whatever wave shape you want.

 

I think what you will need is a 2 or 4 quadrant multiplier. I recall that MC1495 by Motorola is just such a device.

hgmjr

 

If you are simply intending to switch the sine wave on and off 'silently' -like the waveform you have in post #6 -then you could achieve that fairly simply, using a quad opamp oscillator. Something like the attached schematic.
Although the control of the Schmitt trigger on and off is fairly crude and potentially noisy, any 'switch clicks' are attenuated by both the rise and fall time of the triangle wave output, and the fact that the potential of the bandpass output always stays at half rail. The actual bandpass oputput switches on and off 'gently'!

Not really suitable if you need a low distotion sine wave (i.e with a THD of less than 5%). For that you'll need a separate oscillator and envelope controlled VCA circuit, as described by the others.

 

Your phase-shift oscillator circuit ramps up the level of its sine-wave because its gain is too low. It has nothing like an attenuator to slowly ramp down its sine-wave.
It is a simple distorted oscillator.

Usually a Jfet is used as a linear attenuator to ramp up and ramp down a tone level.
The Jfet can keep the distortion low by limiting the max output level before the transistor clips.

Many years ago I used a Jfet to ramp up and down background music on a high quality huge intercom system so that the music faded when an intercom call was received and ramped up the music when the call ended.

Thankyou for your comments. I learned few basic things.

 

let the ossc. run all the time and then modulate it. You would also need a second signal for the modulation, which could have any shape you want. For modulation you need either a voltage controlled ( in amplitue ) amplifier ( or for just on off, an enable disable pin ) amplifier. More generally a 3 or 4 quadrant amplifier ( there are ic's for this ).

Hi russ_hensel , I agree what suggested. As you and "hgmjr" siad 3 or 4 quadrant amplifier(MC1495 or I found few as well after your comments MC1496 , AD630). I am looking for this type of chips(but these chips stopping to desing my own circuit eventhough I am not good designer...) I wiil order MC1496.

However you frequencies are so low that you could also accomplish all of this with a microcontroller and dac programmed for whatever wave shape you want.[/QUOTE

I am using here for only single application, I will go for microcontroller if I use more than one applications.
But I am still intersted to know how exactly will it(microcontroller)work at less than 1KHz,outputs with varying amplitude.

 

I think what you will need is a 2 or 4 quadrant multiplier. I recall that MC1495 by Motorola is just such a device.

hgmjr

Hi hgmjr, thankyou for your valuable information. I am looking for these type chips(MC1495).

 

If you are simply intending to switch the sine wave on and off 'silently' -like the waveform you have in post #6 -then you could achieve that fairly simply, using a quad opamp oscillator. Something like the attached schematic.
Although the control of the Schmitt trigger on and off is fairly crude and potentially noisy, any 'switch clicks' are attenuated by both the rise and fall time of the triangle wave output, and the fact that the potential of the bandpass output always stays at half rail. The actual bandpass oputput switches on and off 'gently'!

Not really suitable if you need a low distotion sine wave (i.e with a THD of less than 5%). For that you'll need a separate oscillator and envelope controlled VCA circuit, as described by the others.

Thank you for your CKT, and information . It is really helpfull.

 

Hi will go for quadrant amplifier, as few people suggested . In mean time I like one basic question.........

While this project workout first I tried Low distortion sine wave
wein bridge oscillator. I tried in simulator It given square wave output instead of sine wave why?.
What am I doing wrong? Correct me......

 

Hi will go for quadrant amplifier, as few people suggested . In mean time I like one basic question.........

While this project workout first I tried Low distortion sine wave
wein bridge oscillator. I tried in simulator It given square wave output instead of sine wave why?.
What am I doing wrong? Correct me......

Typically a sign of too much gain around the positive feedback loop. Geting the gain just right can be difficult. In the old days they sometimes used a lamp filament to get it just right. Google should tell you more.

 

Yet another question.. for same project.. ..

I want converts square wave into envelope with almost equal rise and fall time as show in fig..

Tr = 10ms, Td= 180ms, Tf=10ms (file attached)

Any circuit ideas .. help me... how can i achieve this.. Thankyou in advance..

 

Continuation for my previous post I tried with 555 timer(circuit attached). but capacitor discharging slowly. so. it's out of shape.. and
also.. with this circuit I am unable to adjust the Rise, Fall and widht of the signal properly.. so could you help in this(for circuit idea. or implementation ) issue. Thank you for all your support.