Serial control and waiting for a rsponse - c

Question

I am using an esp 8266 to control an Epson projector over its serial line. I am using a computer and OSC to call functions on the esp that run Epson serial commands. The command I'm having trouble implementing is zoom. The Epson Serial command to zoom the lens in 1 "click" is
ZOOM INC\r
Once the projector executes the code it returns either a : or :ERR. In my function it is suppose to execute the command several times depending on what the user inputs. In my function I want to wait until the projector responds before executing the command again, and this is what I have been trying.
void zoom_inc(OSCMessage &msg){
OSCMessage qLab_msg("/cue/p0/name");
Serial.print("Zoom ");
lock = 1;
char cmd[10] = "ZOOM INC\r";
if(msg.getInt(0) < 0){
cmd[5] = 'D';
cmd[6] = 'E';
}
int high = (abs(msg.getInt(0)) > 50)? 50 : abs(msg.getInt(0));
Serial.print(cmd);
Serial.print(" ");
Serial.print(high);
Serial.println(" times");
unsigned long startTime;
unsigned long currentTime;
unsigned long diff;
boolean response = false;
String readString; //create response string
for(int i = 0; i < high; i++){
projSerial.write(cmd);
startTime = millis();
while(!response){
while (projSerial.available() > 0) { //look for projector response
Serial.write(projSerial.read());
delay(3);
char c = projSerial.read();
readString += c;
}
readString.trim(); //clean projector response
if(readString.length() == 1){
Serial.println("Read Data");
Serial.println(readString.length());
Serial.println(readString);
Serial.println("------------------------------------");
response = true;
}
currentTime = millis();
diff = currentTime - startTime;
if(diff >= 5000 || diff < 0){
Serial.println("Timeout");
response = true;
}
}
delay(200);
}
qLab_msg.add("Zoom Incremental");
Udp.beginPacket(qLabIP, qLabPort);
qLab_msg.send(Udp);
Udp.endPacket();
qLab_msg.empty();
}
This doesn't work because it only does about half of what its suppose to. For example if the user sends 30 it only does 14

Answer 1

This looks suspicious:
Serial.write(projSerial.read());
delay(3);
char c = projSerial.read();
readString += c;
You've just read two characters from projSerial. One got echoed to your main serial port, and the other will be added to the string. Losing approximately every other character from the projector's response seems consistent with getting only about half the steps you expected.
Try:
char c = projSerial.read(); // read it just once
Serial.write(c);
readString += c;
I assume the delay(3) was from an earlier guess.