RC Circuit discharge simulation project on FPGA

Hey, i am struggle with a digital design project and i need suggestion.

First I would like to explain my project a little bit.
This project related to how to implent a numeric methods and prepare a module to this operation.

Description of the project: Initial voltage of capacitor will be adjust with 8 switches on spartan board and Vo value will be set with 1 button.
While discharging capacitor, Voltage value of capacitor will be shown on the 4 digit 7-segment display unit. R=2 and C=15. They are constant.

You know discharge equation is included exponential expression. I figured out this step by numeric methods. I derivated Taylor series to 4th element such as 1+(t/RC)+((t/RC)^2/2!)+((t/RC)^3/3!)+((t/RC)^4/4!). This equation is equal to be exp(t/RC) and It lets me to obtain this function Vc(t)=Vo/exp(t/RC).

I'll use a frequency divider to get 1Hz'ed clock to calculate Vc value for each t value. And will display this value on display unit.

I figured out how to display each digit of any 3 digit value seperately on 7-segment.


I have stucked on the how to perform ( 1 + (t/30) +((t/30)^2/2)+((t/30)^3/6)+((t/30)^4/24) ).

Do you have any guess about this issue ?

The easy, brute-force approach would be to use a look-up table. Depending on the precision required, this may or may not work for your application.

I found ** exponential operand. But i could not achieved using of that operand.

You can't synthesize that exponentiation operator.

If you can't use a lookup table, you're going to have to perform multiplication and division. It can be done (in fact, it's done all the time), but it gets messy in an FPGA.

More detailed description of the project:
RC circuit simulation: Initial capacity voltage will be adjusting by using 8 switch and 1 push button. The serial RC circuit will simulate discharging of capacitor. Vcapacitor will be displayed on 7-segment indicators consistently. R and C values are fixed and R= 2 ohms, C=15 farad.

I have described my problem above. Could you do a favor by posting related topics or projects to me ?

I would suggest a different approach. Time discrete simulation of the first order differential equation: Vc(t+1) = Vc(t)*(1-dt/RC).

i wish i figure out how to use real numbers and don't get ''Illegal operation with real number.'' error. I need to perform a calculation such as x*0.956.

Ty for you replies. I have changed my aspect. Now using this approach and it helped me a lot. b=a*35 then c=b/100 instead of a*0.35.

b=a*35 then c=b/100 instead of a*0.35

Click to expand...

In FPGA we prefer binary fixed point numbers with powers of two as scaling factor. Instead of calculating a divison like c=b/100 we get e.g. c=b/128 which is just a shift operation. In VHDL, the IEEE fixed point package gives you the option to write arithmetic operation with fixd point numbers without thinking about the implementation details.

FvM said:

In FPGA we prefer binary fixed point numbers with powers of two as scaling factor. Instead of calculating a divison like c=b/100 we get e.g. c=b/128 which is just a shift operation. In VHDL, the IEEE fixed point package gives you the option to write arithmetic operation with fixd point numbers without thinking about the implementation details.

Click to expand...

Then i need to perform b=a*45 and c=b/128 calculations to get 0.35, right ?

Then i need to perform b=a*45 and c=b/128 calculations to get 0.35, right ?

Click to expand...

Yes, that's the basic operation for the suggested fixed point or "fractional" arithmetic.

I tried your advicce and divide by 16384 instead of 10000 and LUT usage decreased dramatically. ^^