I'm trying to get the fourier series function(s) to work for a square wave with duty cycles other than 50% ie rectangular wave.

```
squareWave[t_, period_, duty_] := UnitBox[Mod[t/period, 1.]/(2. duty)]    
xx[t_] := squareWave[t, 10, 0.8]    
Plot[xx[t], {t, -10, 10}, Background -> Gray]
curvexx = FourierTrigSeries[xx[t], t, 10];  
Plot[curvexx, {t, -10, 10}, Background -> Gray]

```

that's my code, set up squarewave, check by plotting (alright so far), take fourier series, check by plotting and it's wrong but why where did I go wrong?