How to build ColorFade?

[shinchan]

Hi, I'm a 2nd yr IT student, an extreme novice at electronics. We have a project in Basic Electronics class and we are to present and explain a device using two or more transistors by Wednesday. After my long search in google, I found a simple(I think) device called ColorFade from this page.

Right now I have Multisim 10 Student Version but I can't manage to simulate it (first time to use a SPICE). I have no idea how to put the LM324 as shown in the schematic because multisim gives me this triangle LM324N with only 5 connections. And after that, how do I simulate and see actuall LED's light fade(if it is possible)? Please help! Thanks!

ColorFade Schematic

[lacy]

I am not going to give you a complete solution here because I think it would be better for you to try an firgure out as much as possible own your own (this is the best learning tool I have found that works). What I will do is give you some hints. The LM324 is a multisiection component. When you place this component Multisim should prompt you to place section A then it will continue to do so untill the last section of this IC is placed.  I will include a screen shot showing this prompting dialog box. After all sections are placed look very carefull at each triangle with its 5 pins and you will notice little number beside them (you may have to zoom in a little to clearly see them). These represent the IC package pin numbers. You wire these pins up to the corresponding pins in the picture..

As far as the second part. I will have to get back to you on this once I have entered it into Multsim and tried a few tests.

I hope this helps get you started in the right direction. I could have always posted a completed Multsim file, but I do not believe that would help you to learn. If someone else does the work for you then you haven't really learned anything. I am not trying to be a terrible person, but this is my philosophy when it comes to learning. Learning by doing is what I have always stood by.

If you would get to a point where you just can't acommplish this on your own no matter how hard you have tried, then I will be more than happy to post something for you.

Here's the screenshot I was referring to.

[lacy]

I have enter the circuit into Multisim and got it simulating. I think I have enough information to answer the second part of your question as I understand it.

You are not going to be able to see the LED's in the simulator getting dimmer and fading out. You can see it in the voltage waveform, but the LED's will remain "lit" until a certain threshold is reached and then just cut off or on.

[shinchan]

Ok I've attached what I've made so far, but simulation gives me an error.

I'm starting to think that this device is too hard for a novice like myself. I've been googleling for hours to understand this circuit and all I find is "electronics language" too technical terms. I really need to learn all the basics and fundamentals(I didn't absorb much from our professor in electronics, he's really bad at teaching).

I also agree with that learning tool but for me, I think "Interest" is the best learning tool.

[shinchan]

Here's the error log

[lacy]

O.K. You seem to have done a good job on this so I will post both working ciruits and give you an explaination of what I did to get them to work. Some of this has to do with the way the simulator has to be set up for oscillator type circuits that you may not familiar with.

First, I labeled some corrections on the schematic for you to look at. When dealing with oscillators the simulator has to be set-up to the setting "set to zero". This is accomplished by going to SIMULATE>INTERACTIVE SIMULATION SETTINGS>INITIAL CONDITIONS. Then in the drop down box selecting Set To Zero.

The Second thing is that the op amp model that was selected did not simulate correctly. This was not your fault and is a problem with the model in the master database. There are some op amp models that I have witnessed that do not seem to function correctly. The only thing I can suggest in this situation is that if you know it should work and doesn't try a different model. These are listed in the parts selection dialog box on the right that says Model manuf./ID.

The first circuit is your corrected circuit and the second one is the one from your first post that I wired up yesterday.

I hope this helps and I really wish that you do not get discouraged in electronics. It can be fustrating at times, but it is an exciting and rewarding field of study. I have been in the business in one way or another for about 20 years as an electronics technician and I find that there are still things that I am learning about it. I only design circuits for my own personal use and do that mainly as a hobby. Most of the time I use Multisim to anaylze and troubleshoot existing circuits. Once you get a grip on the basics of electronics and Multisim then it will seem so easy after that.

Hear are your 2 circuits.

[shinchan]

Thank you very much! Sorry if I'm asking too much but can you tell me what's the storyboard behind the circuit? What makes it do dynamic changing of voltage that makes the LEDs light fade(if I'm correct)? What does the straight line output from the Osilloscope Viewer mean? From what I know, DC is a staight line at the positive y-axis, does this mean that the circuit did not change the DC wave(straight line)?

[lacy]

From just my analysis, the two op-amp sections form an oscillator/comparator between two threshold voltages controlled by the  two 47K resistors tied to Pins 3 and 6 of the op amps.  When the threshold voltage is below a certain value Q2 will conduct causing the led to light. This voltage wil slowly rise. This is caused by the charging and discharging of the capacitor.As it slowly rises the base drive to Q2 decreases the same amount. This provides less and less current to the LED and it will eventually not have enough current to remain on. As the voltage continues to rise eventually Q2 will stop conducting A point is reached where the base of Q1 is now becoming more and more positive. This allows it to start conducting and provide more current to it's LED and  it will start to come on.. The only thing is that the fading is not seen in the simulator because the models for the LEDs operate at a certain cut off and cut on current and there is not an in-between with them.

I hope I explained it well enough for you to understand as I am not the best at explaining circuits. I can see it in my head, but putting it down in words in hard for me to do.

I will enclose the circuit again. This time with the scope adjusted properly so you can see the triangular wave that the op-amps produce to achieve this. I also sped up the simulator a bit so this can be seen more quickly Notice that there is a DC Voltage but it has a sine wave in conjuction with it. This is what I refer to as a DC Voltage with AC riding on it. It would be more conventionally called a DC Voltage with an AC Ripple.

I hope this helps.

[shinchan]

Your explanation really helped our project. Thank you very much!
Next semester we will have Logic Circuits if I'm correct, I hope I'll enjoy that subject to me as a programming hobbyist( I do C / Java ).
Thanks again!