# Wasn't sure where to put this - Lowpass Filter in Excel

1. Dec 15, 2013

### BiGyElLoWhAt

Wasn't sure where to put this -- Lowpass Filter in Excel

Ok I need some excel help, I need to model a sawtooth wave mathematically (done) and then I need to put it through a lowpass filter, but I need to do it in excel. My prof expects an excel spreadsheet, and I have no clue how to put it in there. On wolfram I use plot Ʃ[sin(2*n*pi)/(n*pi)] and that works when I take it out 100 or so terms, but excel doesn't like those kinds of functions.

How can I put it in there?

2. Dec 15, 2013

### ModusPwnd

You are summing over n right? In excel I would just make one column "n" and number it from 1 to 100 or so. Then the column next too it would be sin(2*n*pi)/(n*p)+"previous cell". Here "n" would be a reference to the cell in the adjacent column and "previous cell" would be the cell above which has the rest of the terms of the sum. Does that seem right?

3. Dec 15, 2013

### BiGyElLoWhAt

That seems somewhat right, but I need an x in there. It's actually sum sin(2npix)/npi

4. Dec 16, 2013

### cpscdave

When I was learning Fourier Series, what I would occasionally do to verify my answers was to plot the first N series and see if it looked like what I started with.

To accomplish this what I did is along the first Collum I had 1->N
Then along the first row I put -k->k (the period of the function)
Then just filled in the function information

for you it'd look something like =sin(2*$A1*pi()*A$1)/(2*$A1*pi())) The$A1 being your N term and the A\$1 being your x term, set so as you pull the formula they stay in the right column/row.

Then in row N+1 you sum the collum and plot that

Hope that makes sense :D

5. Dec 16, 2013

### rude man

You haven't specified your lowpass transfer function.

So let's assume it's a 1st order lowpass: 1/(Ts+1) where 1/T = corner radian frequency.

I would write an equivalent finite-difference equation for this function, then pass your triangular wave thru it and get the output. The output can then be plotted by excel's plotting facility.

You need to specify T and you also need to specify the frequency of your triangular input.

Last edited: Dec 17, 2013