diff --git a/cubesatsim/cubesatsim.ino b/cubesatsim/cubesatsim.ino
index d790cfd9..f400a46d 100644
--- a/cubesatsim/cubesatsim.ino
+++ b/cubesatsim/cubesatsim.ino
@@ -55,6 +55,16 @@ void setup() {
 	
   config_gpio();
 	
+  pinMode(PI_3V3_PIN, INPUT); 	
+  Serial.print("Pi 3.3V: ");
+  Serial.println(digitalRead(PI_3V3_PIN));
+  if (digitalRead(PI_3V3_PIN) == LOW)  {
+    Serial.print("Pi Zero present, so running Payload OK code instead of CubeSatSim code.");
+    start_payload();	
+    while(true)	 { 
+	  payload_OK_only();    
+    }
+  }
   read_reset_count();	
 
 //  mode = FSK; // AFSK;		
@@ -2271,6 +2281,194 @@ void read_payload()
 
 //  delay(100);
 }
+
+void payload_OK_only()
+{
+  payload_str[0] = '\0';  // clear the payload string
+	
+  if ((Serial.available() > 0)|| first_time == true)   // commented back in
+  {
+    blink(50);
+    char result = Serial.read();
+    char header[] = "OK BME280 ";
+    char str[100];
+	  
+    strcpy(payload_str, header);
+//    print_string(str);		  
+    if (bmePresent) 
+//    	sprintf(str, "%4.2f %6.2f %6.2f %5.2f ", 
+   	sprintf(str, "%.1f %.2f %.1f %.2f ", 
+	  bme.readTemperature(), bme.readPressure() / 100.0, bme.readAltitude(SEALEVELPRESSURE_HPA), bme.readHumidity());
+    else
+        sprintf(str, "OK BME280 0.0 0.0 0.0 0.0 "); 
+    strcat(payload_str, str);
+
+    if (mpuPresent) 	 { 
+//    print_string(payload_str);	
+    mpu6050.update();
+
+//    sprintf(str, " MPU6050 %5.2f %5.2f %5.2f %5.2f %5.2f %5.2f ",
+    sprintf(str, " MPU6050 %.1f %.1f %.1f %.1f %.1f %.1f ",
+      mpu6050.getGyroX(), mpu6050.getGyroY(), mpu6050.getGyroZ(), mpu6050.getAccX(), mpu6050.getAccY(), mpu6050.getAccZ()); 
+    
+    strcat(payload_str, str);
+//    print_string(payload_str);
+    }
+    if (result == 'R') {
+      Serial.println("OK");
+      delay(100);
+      first_time = true;
+      setup();
+    }
+    else if (result == 'C') {
+      Serial.println("Clearing stored gyro offsets in EEPROM\n");
+      EEPROM.put(0, (float)0.0);
+      first_time = true;
+      setup();
+    }
+    if ((result == '?') || first_time == true)  // commented back in
+    if (true)
+    {
+      first_time = false;
+      if (bmePresent) {
+        Serial.print("OK BME280 ");
+        Serial.print(bme.readTemperature());
+        Serial.print(" ");
+        Serial.print(bme.readPressure() / 100.0F);
+        Serial.print(" ");
+        Serial.print(bme.readAltitude(SEALEVELPRESSURE_HPA));
+        Serial.print(" ");
+        Serial.print(bme.readHumidity());
+      } else
+      {
+        Serial.print("OK BME280 0.0 0.0 0.0 0.0");
+      }
+    if (mpuPresent) 	 { 
+      mpu6050.update();
+
+      Serial.print(" MPU6050 ");
+      Serial.print(mpu6050.getGyroX());
+      Serial.print(" ");
+      Serial.print(mpu6050.getGyroY());
+      Serial.print(" ");
+      Serial.print(mpu6050.getGyroZ());
+
+    Serial.print(" ");
+    Serial.print(mpu6050.getAccX());   
+    Serial.print(" ");
+    Serial.print(mpu6050.getAccY());   
+    Serial.print(" ");
+    Serial.print(mpu6050.getAccZ());  
+    }
+	    
+    sensorValue = analogRead(A3);
+    //Serial.println(sensorValue);  
+    Temp = T1 + (sensorValue - R1) *((T2 - T1)/(R2 - R1));
+
+    
+    Serial.print(" XS ");
+    Serial.print(Temp);   
+    Serial.print(" ");
+    Serial.println(Sensor1);               
+  
+  if (mpuPresent) 	 { 	    
+    float rotation = sqrt(mpu6050.getGyroX()*mpu6050.getGyroX() + mpu6050.getGyroY()*mpu6050.getGyroY() + mpu6050.getGyroZ()*mpu6050.getGyroZ()); 
+    float acceleration = sqrt(mpu6050.getAccX()*mpu6050.getAccX() + mpu6050.getAccY()*mpu6050.getAccY() + mpu6050.getAccZ()*mpu6050.getAccZ()); 
+//    Serial.print(rotation);
+//    Serial.print(" ");
+//    Serial.println(acceleration);
+ 
+    if (acceleration > 1.2)
+        led_set(greenLED, HIGH);
+    else
+        led_set(greenLED, LOW);
+        
+    if (rotation > 5)
+        led_set(blueLED, HIGH);
+    else
+        led_set(blueLED, LOW);  
+    } 
+   }    
+  }
+
+  if (Serial1.available() > 0) {
+ 
+    blink(50);
+    char result = Serial1.read();
+    //    Serial1.println(result);
+
+    if (result == 'R') {
+      Serial1.println("OK");
+      delay(100);
+      first_read = true;
+      setup();
+    }
+
+    if (result == '?')
+    {
+      if (bmePresent) {
+        Serial1.print("OK BME280 ");
+        Serial1.print(bme.readTemperature());
+        Serial1.print(" ");
+        Serial1.print(bme.readPressure() / 100.0F);
+        Serial1.print(" ");
+        Serial1.print(bme.readAltitude(SEALEVELPRESSURE_HPA));
+        Serial1.print(" ");
+        Serial1.print(bme.readHumidity());
+      } else
+      {
+        Serial1.print("OK BME280 0.0 0.0 0.0 0.0");
+      }
+      mpu6050.update();
+
+      Serial1.print(" MPU6050 ");
+      Serial1.print(mpu6050.getGyroX());
+      Serial1.print(" ");
+      Serial1.print(mpu6050.getGyroY());
+      Serial1.print(" ");
+      Serial1.print(mpu6050.getGyroZ());
+
+    Serial1.print(" ");
+    Serial1.print(mpu6050.getAccX());   
+    Serial1.print(" ");
+    Serial1.print(mpu6050.getAccY());   
+    Serial1.print(" ");
+    Serial1.print(mpu6050.getAccZ());   
+
+    sensorValue = analogRead(A3);
+    //Serial.println(sensorValue);  
+    Temp = T1 + (sensorValue - R1) *((T2 - T1)/(R2 - R1));
+
+    Serial1.print(" XS ");
+    Serial1.print(Temp);   
+    Serial1.print(" ");
+    Serial1.println(Sensor2);              
+     
+    float rotation = sqrt(mpu6050.getGyroX()*mpu6050.getGyroX() + mpu6050.getGyroY()*mpu6050.getGyroY() + mpu6050.getGyroZ()*mpu6050.getGyroZ()); 
+    float acceleration = sqrt(mpu6050.getAccX()*mpu6050.getAccX() + mpu6050.getAccY()*mpu6050.getAccY() + mpu6050.getAccZ()*mpu6050.getAccZ()); 
+//    Serial.print(rotation);
+//    Serial.print(" ");
+//    Serial.println(acceleration);
+
+    if (first_read == true) {
+      first_read = false;
+      rest = acceleration;
+    }
+
+    if (acceleration > 1.2 * rest)
+        led_set(greenLED, HIGH);
+    else
+        led_set(greenLED, LOW);
+        
+    if (rotation > 5)
+        led_set(blueLED, HIGH);
+    else
+        led_set(blueLED, LOW);
+    }
+  }
+
+  delay(100);
+}
 	
 /*
 void eeprom_word_write(int addr, int val)