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#1
12-05-2007, 10:03 PM
 FredM Senior Member Join Date: Dec 2005 Posts: 124
Electronics Formula Excel Cheat Sheet Project

I needed to calculate the voltage on a capacitor after a given time, and also needed to calculate the time required to charge a capacitor to a given voltage.. maths being rusty (and losing my SC which had all the formulas programmed in ) I resorted to Excel.

The attached .xls (in .zip) may be of use to others.. it contains 2 simple routines..

1.) Given applied voltage, R, C, and time (t), it outputs the instantaneous voltage across the capacitor at t.

2.) Given applied voltage, R, C, and the voltage required across the capacitor, it outputs the time at which this voltage appears across the capacitor.

You will need the LN() function installed in Excel or (other spreadsheet)
Attached Files
 Capacitor Voltage time.zip (11.7 KB, 1686 views)

Last edited by FredM; 12-05-2007 at 10:07 PM.
#2
12-06-2007, 03:26 AM
 agentofdarkness Junior Member Join Date: Oct 2007 Posts: 42

If you have an RC circuit, you can solve the following differential equation:

EMF = Vr + Vc (Kirchoff's Voltage Rule)
Vr = IR = (dq/dt)*R
Vc = Q/C
EMF = (dq/dt)*R + (Q/C)

After solving the 1st order differential equation, you get
q = C(EMF)(1-e^(-t/(RC)))
i = dq/dt = (EMF/R)e^(-t/(RC))
This is for a DC circuit where the capacitor and resistor are in series.
#3
12-06-2007, 09:29 AM
 Dave Senior Member Join Date: Nov 2003 Posts: 6,961 Blog Entries: 17

Quote:
 Originally Posted by FredM I needed to calculate the voltage on a capacitor after a given time, and also needed to calculate the time required to charge a capacitor to a given voltage.. maths being rusty (and losing my SC which had all the formulas programmed in ) I resorted to Excel. The attached .xls (in .zip) may be of use to others.. it contains 2 simple routines.. 1.) Given applied voltage, R, C, and time (t), it outputs the instantaneous voltage across the capacitor at t. 2.) Given applied voltage, R, C, and the voltage required across the capacitor, it outputs the time at which this voltage appears across the capacitor. You will need the LN() function installed in Excel or (other spreadsheet)
This is a pretty good idea. I usually resort to the old pen and paper.

It might be an idea to run a small project that implements and graphs all of the major electronics formula and functions for people new to the subject. Perhaps this could be the spring board from which to build from.

I'd be interested in helping out.

Dave
#4
12-09-2007, 04:40 AM
 FredM Senior Member Join Date: Dec 2005 Posts: 124

Quote:
 Originally Posted by Dave This is a pretty good idea. I usually resort to the old pen and paper. It might be an idea to run a small project that implements and graphs all of the major electronics formula and functions for people new to the subject. Perhaps this could be the spring board from which to build from. I'd be interested in helping out. Dave
Hi Dave -

Non-linear stuff is where I have problems, which is why I resorted to Excel.. However, there is no reason why a single spreadsheet could not be produced which contains the major formulas - from ohms law up..

If a worksheet was done for each 'group', this could be quite an interactive project - and need not be limited to formulas.. Simple circuits (standard op-amp configurations, 555 timers etc) could be 'simulated' quite simply.

I attach an example, based on the computations of the last..
This is a spreadsheet to calculate frequency and M/S ratio of 555 timer acting as oscillator..

I cannot spend any more time on the above 'project' at the moment, but would be happy to participate in the new year.. I dont think much co-ordination is required though.. If peeps leave worksheets unprotected, and are free to use / modify what has been created, or create new sheets.. they could be pasted here and collated later.
Attached Files
 555 Oscillators.zip (32.7 KB, 595 views)
#5
12-09-2007, 04:06 PM
 Distort10n Senior Member Join Date: Dec 2006 Posts: 429

Hello Dave,

This is a really good idea. Many engineers that I work with use Excel for everything. I have several Excel files myself showing how to calculate the input common mode range of single supply in-amp.

Maxim also has an application note called "Exact Circuit Analysis" which uses Excel to calculate the impedance of an RC circuit. It then uses it to calculate the phase shift in the open loop curve of an op-amp.

I think this would be a great project for things like Ohm's law, Power, Reactance, transistor curves, etc.
#6
12-09-2007, 04:15 PM
 Dave Senior Member Join Date: Nov 2003 Posts: 6,961 Blog Entries: 17

Hi FredM and knightofsolamnus,

I'm glad we think this may be a good idea; to honest I'm surprised we haven't embarked on something like this before. I am willing to act as a coordinator, unless someone has the desire to take charge.

FredM's spreadsheet is a good starting point. knightofsolamnus, if you want to upload your spreadsheets, I can merge them with FredM's and a couple of working spreadsheets I have and we can get the ball rolling. I can then post up a first version covering the basics.

If FredM is happy for me to do so, I will change the thread name to something that better reflects the objectives of the project and I will stick it to the top of the Electronics Resources forum.

If anyone else wishes to get involved please post and get involved.

Dave
#7
12-09-2007, 09:04 PM
 FredM Senior Member Join Date: Dec 2005 Posts: 124

Quote:
 Originally Posted by Dave If FredM is happy for me to do so, I will change the thread name to something that better reflects the objectives of the project and I will stick it to the top of the Electronics Resources forum. Dave
I am more than happy with this..
#8
12-10-2007, 07:14 AM
 Dave Senior Member Join Date: Nov 2003 Posts: 6,961 Blog Entries: 17

Quote:
 Originally Posted by FredM I am more than happy with this..
Done. I'll get grafting on some basics. If anyone has any formula that would be good for putting into this, please let me know.

I hope we can have a good working version in the new year.

Dave
#9
12-29-2007, 01:10 AM
 Distort10n Senior Member Join Date: Dec 2006 Posts: 429

Here is an Ohm's Law calculator. I was going to use VB scripts in Excel (bought a book to learn how to do it) but just relied on simple Excel formulas for now.
Attached Files
 Ohms Law.zip (10.6 KB, 667 views)
#10
12-30-2007, 10:05 AM
 Dave Senior Member Join Date: Nov 2003 Posts: 6,961 Blog Entries: 17

Quote:
 Originally Posted by knightofsolamnus Here is an Ohm's Law calculator. I was going to use VB scripts in Excel (bought a book to learn how to do it) but just relied on simple Excel formulas for now.
Hi knightofsolamnus,

Good starting point and it looks quite snazzy with the colours and chart in the middle.

I did consider the options of using VB macros, and even the idea of doing it in C++, however this is intended to be a simple calculator type application for general use. Why spend time implementing features that are readily available in Excel (I'm sure we will hit a stumbling block at some point when a bit of VB code will be needed).

I encourage anyone else who has Excel worksheets for calculating values in just about any electronics applications to submit it - it would be great to have a collective effort covering a wide range of formulas.

Dave

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