TRIANGLE WAVE
GENERATOR
SIGNAL GENERATOR
I find it fun and
challenging to
create waveforms using programming and the triangle wave was no exception. You
can download the file here
Triangle_Wave.xls.
The triangle wave can be defined by a few parameters.
V1 
Voltage level 1 (initial voltage)
V2 
Voltage level 2
T1  Period that waveform
ramps from V1 to V2
T2  Period that waveform
ramps from V2 to V1
One way to accomplish this waveform is by
using voltage slopes and IF, THEN statements.

Function Tri_Wave(t, V1, V2, T1,
T2)
' *************************************************************
' Generate Triangle Wave
'
' t  time
' V1  voltage level 1 (initial voltage)
' V2  voltage level 2
' T1  period ramping from V1 to V2
' T2  period ramping from V2 to V1
'***************************************************************
Dim t_tri, dV_dt1, dV_dt2 As Double
Dim N As Single
' Calculate voltage rates of change (slopes) during T1
and T2
dV_dt1 = (V2  V1) / T1
dV_dt2 = (V1  V2) / T2
' given t, how many full cycles have occurred
N = Application.WorksheetFunction.Floor(t / (T1 + T2), 1)
' calc the time point in the current triangle
wave
t_tri = t  (T1 + T2) * N
' if during T1, calculate triangle value using
V1 and dV_dt1
If t_tri <= T1 Then
Tri_Wave = V1 + dV_dt1 * t_tri
' if during T2, calculate triangle value using
V2 and dV_dt2
Else
Tri_Wave = V2 + dV_dt2 * (t_tri  T1)
End If
End Function

To see the VBA code hit ALTF11 and double
click on the Modules > Module1 in the VBA Project window.
WAVEFORM PARAMETERS AND FUNCTION CALL
The description of the triangle wave is
entered in these cells.
V1 
1 
V2 
1 
T1 
0.005 
T2 
0.005 




dT 
0.0002 
The time column is generated by entering the
time increment dT at location C14. Each time point is simply the previous
time point plus the delta, A17+$C$14. Note, that C14 is a fixed reference
point.
The cells in the Vtri column holds the
function call. The entries in this column looks
like
=Tri_Wave(A17,$C$9,$C$11,$C$12,$C$10)
where A17 is the current time point and C9
through C10 hold the triangle. I still get a kick out of changing the
parameters and then watching the plot change.
CREATING THE WAVEFORM
How do you create a triangle wave? The
waveform simply ramps linearly from V1 to V2 during T1, and then from V2 to
V1 during T2. Therefore, you need to calculate the slope for both cases.
dV_dt1 = (V2  V1) / T1
dV_dt2 = (V1  V2) / T2
Next, the function could create many triangle
cycles. So the big question is this, where in the current cycle are you. To
find out, you need to adjust the current time by subtracting off how many
whole cycles (N) have already occurred.
' given t,
how many full cycles have occured
N = Application.WorksheetFunction.Floor( t/(T1 + T2), 1)
' calc the time point in the current triangle wave
t_tri = t  (T1 + T2) * N
The first calculation above calculates the
ratio of current time to the triangle's period, t/(T1+T2), and then rounds
down using the Floor function. (NOTE: Because VBA does not directly support
the Floor function, you need to call it from Excel with the following:
Application.WorksheetFunction.Floor.)
The next calculation finds the time point (t_tri) in the current cycle by
subtracting off N whole cycles worth of time. Now we can use t_tri to
calculate the waveform.
The function uses an IF,THEN, ELSE
statements to determine if t_tri occurs is period T1 or T2. If in period T1, the
waveform is simply the initial voltage V1 plus t_tri multiplied by the slope dV_dt1.
If t_tri <= T1 Then
Tri_Wave = V1 + dV_dt1 * t_tri
If in period T2, the waveform is a function
of V2 and the slope dV_dt2.
Else Tri_Wave = V2 + dV_dt2 * (t_tri  T1)
Note that the time is adjusted using (t_tri 
T1) to determine how much time has elapsed in T2.
Vary the parameters and see the plot change.
Decrease or Increase dT to get more or less points per waveform. We'll use
this ramp in later topics as inputs to circuits like amplifiers and ADCs.
YOUR TURN
 Write a Pulse function to
create a repeating series of pulses. Like the triangle wave, define T1
and T2 along with their discrete voltage levels. Use the triangle wave
file above as a starting point..
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