# simple equation solver software

Discussion in 'Electronics Resources' started by laserr69, Jul 25, 2015.

1. ### laserr69 Thread Starter New Member

Jul 25, 2015
3
0
I am looking for PC software calculator (free or pay) that would allow me enter simple equations with few variables and save them for specific use.

For example to find out what resistors are needed to obtain a given voltage output for a precision voltage regulator using a TL431 or equivalent:

Vo=(1+ R1/R2)*Vref

Say I want 3.3V for Vo, R1=10k, Vref=2.50. I enter these variables and click solve and the answer comes out: R2=31250. I then can choose the nearest standard value (33K) and solve again for Vo.

I want to save this equation as "TL431 regulator".

The same would apply to V/I calculations for resistor networks, simple RC circuits, etc

I don't want to have to enter the equation every single time, I just want load it by the text name.

Any suggestions?

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,980
1,138
Thinking laterally, if you have LTspice it would be easy to use a respective Behavioral Voltage Source as the solver for each equation.

3. ### laserr69 Thread Starter New Member

Jul 25, 2015
3
0
I don't have LTspice. I just need a simple calculator program where I can save multiple formulas under application name and be able to solve for any variable.

Apr 5, 2008
15,806
2,389
5. ### laserr69 Thread Starter New Member

Jul 25, 2015
3
0
Alec_t,

I thought about your suggestion and perhaps LTspice is the correct answer because I would need to the see the schematic so that I solve for the different resistor/cap values. So it is about time I become familiar with LTspice. Thanks for your suggestion.

6. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
The equation solver add-in in Microsoft Excel works well. You have to enter the equations, and set up the criteria for a solution, e.g. roots of an equation, simultaneous equations, least squares fit through data, etc...

7. ### LDC3 Active Member

Apr 27, 2013
920
160
The free version will allow you to solve for variables, the paid version will do a lot more, maybe even solve equations.

8. ### crutschow Expert

Mar 14, 2008
13,515
3,386
I used to use an HP42S calculator which had a very neat solve function.
You would store an equation in the solver memory with an arbitrary number of up to 6 variables (a simple 3-variable example would be V = I x R).
Then when you run the equation solver for that equation it would show the variables across the bottom of the display (e.g. V I R) with corresponding keys right right below the display becoming soft keys for those variables.
Now you put the numbers in for any two of the three variables (for the simple example) by entering the number and pressing the corresponding soft key (e.g. 3⇒R and 6⇒V). Then pressing the softkey would give the answer 2 (for the current I).
This could be done for any of the three variables in this example by just entering any two of the variable values without having to rearrange the equation. It would then iteratively solve for the unknown.

I did find an HP-42s simulator here which may reproduce that function (which sounds like what you want) but haven't tried it to see if it works.

Last edited: Jul 26, 2015
absf likes this.