Arduino to generate a rising waveform (sine or triangle) - arduino

Question

I would like to apply an increasing voltage and hold to my output from my arduino UNO. I realize that the arduino does not allow me to output analog values, and thus I decided to use an R2R ladder (with R- 22kohms and 2R- 47kohms). This would allow me to convert to an analog voltage. I made use of the eight digital pins on the arduino, to set up an 8 bit R2R ladder. I am able to output a sine wave, with my current setup, but a little bit unsure on how to output a wave which goes up to the maximum value and stops. (i.e. a wave like given in the picture below).
This wave is basically a triangle wave or even a sine wave which goes up to a max value and stays there (with 200 micro second pulse duration).
I have created a visual of my circuit to better demonstrate my problem:
I also attempted my problem, by outputting a sine wave. My code is as follows:
void setup() {
//set pins 0-7 as outputs
for (int i=0; i<8; i++){
pinMode(i, OUTPUT);
}
}
void loop() {
double value =0;
int check=0; int t=0;
while(check==0){
if (value<254){
value = 127+127*sin(2*3.14*t/100);
//this sends a sine wave centered around (127/255 * 5)=2.5V
//max will reach when t=25
PORTD=value;
delayMicroseconds(4); //wait 4 micro seconds
//this means that the max value will reach at ~25*6 =150 microseconds
}
else{
value =255;
PORTD=value; //just output the max of the sine wave (i.e. 255)
delayMicroseconds(50); //delay to ensure total duration is 150+50=200 microseconds
PORTD=0; //output back a 0
check=1; //condition to exit the loop
}
t=t+1;
}
}
For some reason, the pulse generated is not exactly what I am looking for. Is there something I am doing wrong? Or is there a better implementation for something like this? Additionally, if there is something I am missing in my question, please let me know.

Answer 1

I realize that the arduino does not allow me to output analog values
In order to output analog values use one of the analog outputs of the Arduino.
They are marked with a ~
Here' an example from the Arduino reference:
int ledPin = 9; // LED connected to digital pin 9
int analogPin = 3; // potentiometer connected to analog pin 3
int val = 0; // variable to store the read value
void setup() {
pinMode(ledPin, OUTPUT); // sets the pin as output
}
void loop() {
val = analogRead(analogPin); // read the input pin
analogWrite(ledPin, val / 4); // analogRead values go from 0 to 1023, analogWrite values from 0 to 255
}