It's very easy for one tiny thing (like that missed decimal point) to make the simulation very unreliable.

That's a great point. I programmed extensively in Excel for real world users, and you can NEVER anticipate how users will make entries. I had one that entered a "space" when he had no data to enter, but a "space" IS data to Excel. Took forever to see it, because... you can't see a space.

Anyway, if the course was on Excel I'd recommend using all its built in tools for verifying entries (must be numerical, within a certain range, etc.). But I think you can just make sure the documentation spells out the limitations of the simulation. For instance, don't let your 555 simulation run at 10 GHz.

Understanding the limitations of a model is one of the very key concepts of modeling, so hopefully your instructor will be impressed if you demonstrate your understanding of this key concept.

 

It's like looking for an invisible needle in a needle factory then?

 

Exactly. Every set of test data worked, but the real data would blow up every time. Simple in hindsight, but what programmer would ever test for entering a "space"? Well, an experienced programmer learns such things the hard way. And you don't forget stuff like that.

My dad used to say that if you think something is foolproof, it just means you haven't met a fool yet.

 

The trouble with trying to write foolproof programs is that the fools are too ingenious.

RF Cafe has an Excel calculator workbook that's downloadable from their site. Link to their online calculator page:
http://www.rfcafe.com/references/spreadsheets/calculator-list.htm
Description page for the calculator workbook: http://www.rfcafe.com/business/software/rf-cafe-calculator-workbook/rf-cafe-calculator-workbook.htm
Direct link to the .zip file: http://www.rfcafe.com/business/software/download/RFCafe-Calculator-Workbook-v7p0.zip
Many more links to calculators on this page: http://www.rfcafe.com/references/calculators.htm

 

Thanks for all your help, can I ask what the constants 1.44 and 0.7 are representing?

 

I think they are just numbers that fit, however, I'll check my book at lunchtime. It,s in the boot of the car!

 

In 2 and a half hours.

 

Ok, thanks a lot. Just need them to finish my write up in my report.

 

One more thing, any suggestions on what else I could include about the 555 Timer, like what other parts can I analyze besides frquency?

 

Show the duty cycle = 100 x T1 / ( T1 + T2 )

 

Duh!! I just read that too and I still didn't think to put it in lol

Cheers!!

 

Okay, the numbers 1.44 and 0.7 are just simple constants. If they were any other number, then the equation wouldn't work.

They could be compared to any other constant, like π. What is the number pi? Without going too deep, it isn't a real number (I'll probably get slated for saying that, but it's the best way of describing it off of the top of my head lol!), but pi is incredibly useful when figuring this out (like the area of a circle).

The same applies with the 1.44 and 0.7, except they haven't been named like pi. They are just really useful numbers which are used.

 

I'd go a bit more accurate than that.
I use 0.707107 and it's reciprocal; 1.414213. Not perfect of course, but you'll get far more accurate results than the overly simplified 0.7 and 1.414

 

One more thing, any suggestions on what else I could include about the 555 Timer, like what other parts can I analyze besides frquency?

Show the duty cycle = 100 x T1 / ( T1 + T2 )

You'll really have to show the schematic along with the formulas for on time, off time, and frequency or pulse repetition time. There are quite a few variations on 555 timer circuits.

 

The same applies with the 1.44 and 0.7, except they haven't been named like pi. They are just really useful numbers which are used.

Like π, they have a meaning beyond just a useful number. The sin (or cosine) of 45° is 0.7071, and the reciprocal is 1.4142

 

Thanks for all your help guys, have now got the spreadsheets done and a nice 15 page write up about them, excluding the conclusion!

I have finished well ahead of the time I was expecting so I thought why stop now, could anyone give me something else I could work on to improve my project?

Nothing too complicated, just something as a nice little addition!

Cheers!

 

There's a nice write-up here about characterizing PV panels.

 

How about a BJT simulator? You can put a PictureBox on the spread sheet, add graphics and Labels to it.