Need help with analogue question

[dc22]

Hi,

I need help with an analogue question. Here is the relevant analogue I built in multisim

The question asks to "modify the existing analogue build to achieve an approximate frequency of 1 cycle per second (1Hz) ,include all calculations"?

Thanks

 

[KrisBlueNZ]

That circuit is SO hard to read. You have two nodes connected separately to two separate ground symbols!

This is just a recipe for confusion. It's also an insult to people who try to read the schematic - you're asking people (many people) to spend their time trying to find their way around the circuit because you haven't spent a few minutes to tidy it up. The circuit is probably very simple under all that clutter, and tidying it up will help you follow it a lot better too.

Try these ideas to improve readability.

1. Put a single 0V rail (with the ground symbol) running horizontally (west to east) from one side to the other. Everything that connects to it must be connected using a north-south wire that come from somewhere north of the 0V rail. Apart from the main 0V rail, ALL wires connected to 0V must be north-south, except for SHORT west-east wires with nothing crossing them.

2. Put both batteries with their positive terminals are at the north end, and put them one above the other, at either the west or east side. Run the positive and negative rails along the top and bottom of the diagram with only north-south wires to connect them together.

3. Put the input signal source at the west (left) of the diagram.

4. Change the part number of U1 to something meaningful e.g. LM741.

5. Move text so it doesn't overlap components and is clearly readable.

6. Avoid unnecessary zigs and zags such as the one just to the right of R1. Move components around so they line up, instead of joining them up with staggered lines.

Obviously you don't have to do any of this, but if you want your schematics to be easy to read (by yourself and others) these are good starting points.

Then it should be clear to everyone here what that circuit does. Then we can answer the question!

 

[dc22]

I have changed the circuit around a bit to tidy it up

https://www.mediafire.com/?155y1cgsidfyd6j I'm not sure if you have multisim or not but here is the link to the multisim file if you would be kind enough to tidy up the parts I don't really understand.

Thanks

 

[Arouse1973]

I don't think we will be doing that. But here it is a bit neater.
Adam

 

[KrisBlueNZ]

OK, here's what I mean by a tidy schematic:



I won't bother describing the changes individually because I already did that in post #2.

This schematic and the scope traces are done with LTSpice, a free circuit simulation tool you can get from http://www.linear.com.

LTSpice doesn't have multimeters, so I've used a "load" symbol for them. It also doesn't have an oscilloscope - monitoring waveforms is done by clicking on the schematic, with the waveform appearing in a separate window above the schematic, as you can see.

As for the question, it seems the answer is pretty simple. The circuit itself isn't an oscillator; it's just an inverting amplifier. It just amplifies (and inverts) whatever signal you put into it; this signal comes from signal generator V3.

At present the signal from V3 is a square wave that's 0V for 0.5 seconds, then 1V for 1 second, repeating. I got those figures from the diagram in post #3. The diagram in post #1 has different timing figures.

As you can see from the green trace on the oscillograph, the total period of this signal is 1.5 seconds. Therefore its frequency is 0.667 Hz. The question asks you to "achieve an approximate frequency of 1 cycle per second (1Hz)". Since the frequency is completely controlled by the settings of signal generator V3, you need to change those settings to give a frequency of 1 Hz, which corresponds to a total period of 1 second, instead of the current settings which give a total period of 1.5 seconds.

 

[(*steve*)]

OK, here's what I mean by a tidy schematic:

Oh, so *that's* what it is

 

[dc22]

OK, here's what I mean by a tidy schematic:

View attachment 13777

I won't bother describing the changes individually because I already did that in post #2.

This schematic and the scope traces are done with LTSpice, a free circuit simulation tool you can get from http://www.linear.com.

LTSpice doesn't have multimeters, so I've used a "load" symbol for them. It also doesn't have an oscilloscope - monitoring waveforms is done by clicking on the schematic, with the waveform appearing in a separate window above the schematic, as you can see.

As for the question, it seems the answer is pretty simple. The circuit itself isn't an oscillator; it's just an inverting amplifier. It just amplifies (and inverts) whatever signal you put into it; this signal comes from signal generator V3.

At present the signal from V3 is a square wave that's 0V for 0.5 seconds, then 1V for 1 second, repeating. I got those figures from the diagram in post #3. The diagram in post #1 has different timing figures.

As you can see from the green trace on the oscillograph, the total period of this signal is 1.5 seconds. Therefore its frequency is 0.667 Hz. The question asks you to "achieve an approximate frequency of 1 cycle per second (1Hz)". Since the frequency is completely controlled by the settings of signal generator V3, you need to change those settings to give a frequency of 1 Hz, which corresponds to a total period of 1 second, instead of the current settings which give a total period of 1.5 seconds.

Ah many thanks to your contribution.

I put a similar thing to what you are saying. I put basically that since it is just an amplifier, only amplitude changes so to achieve a 1Hz output, a 1Hz input is needed. For that I changed the period on the source to 1 second with a duty cycle of 50%.

Thanks

 

[KrisBlueNZ]

I put a similar thing to what you are saying. I put basically that since it is just an amplifier, only amplitude changes so to achieve a 1Hz output, a 1Hz input is needed. For that I changed the period on the source to 1 second with a duty cycle of 50%.

That's a good explanation. And you showed your calculations for the high and low periods of the square wave based on a 1 Hz frequency?

 

[dc22]

That's a good explanation. And you showed your calculations for the high and low periods of the square wave based on a 1 Hz frequency?

What would those be? sorry for the late reply

 

[KrisBlueNZ]

Well, you worked out that you needed to change the source signal to have a period of 1 second to get a 1 Hz frequency. The calculation is very simple but the question asks you to show it, so you should.