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msp430g2231 and HC-SR04 problem


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Hi

I have the old board with 2231 and tried connecting the ultrasonic sensor without success.

First, here's the code I'm using:

void setup() {
  Serial.begin ();
  pinMode(P1_5, OUTPUT);
  pinMode(P1_4, INPUT);
}

void loop() {
  int duration;
  int distance;
  digitalWrite(P1_5, HIGH);
  delayMicroseconds(1000);
  digitalWrite(P1_5, LOW);
  duration = pulseIn(P1_4, HIGH);
  distance = (duration/2) / 22; //za cm
  Serial.print(distance);
  delay(100);
}

 

The sensor vcc and gnd is connected on external 5v supply from the usb on the board.

The trigger pin is directly connected to P1_5.

The echo pin is connected trough 2 resistors like this

 

                                   GND

                                   | 

                                  |  |

                                  |  | 27Kohm   

                                   |

                                   |--------------------------- P1_4

                                   |

                                 |  |

                                 |  | 18Kohm

                                  |

SENSOR  Echo PIn --|

 

 

So i should probably get around 2.8v output on P1_4 .

On the serial console i just get 0. 

Can someone please suggest whats seems to be wrong with this setup.(the crystal on the board is soldered if it has some importance)                       

 

 

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If you're using the launchpad power, you should probably change the bottom resistor with a 15k version. The launchpad provides 3.6v and accepts vcc-0.7 as its input high. Which would be 2.9; just above your input voltage.

 

Just tried with 15k, no change

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Your voltage divider is good. If you have 5 Volt on the HC-SR04 you should end up with 3.2 volt on P1_4 (27/15 divider).
 
Do you have access to a scope or a logic analyzer to look at the signal on P1_4?

No scope. I found fluke graphic multimeter but probably signal is fast to be measured. There's a ttl test with beep on it and when i make the delay between measurements 1 second i get the beep in that interval both on the echo and trig. pin. So i guess it works .

I though there's a problem in the software. Also found an arduino example with the same sensor where the 1000 microseconds is replaced with 10. Tried that an still no sucess. 

When i try to print the duration variable on the console it's also 0 so seems there's no echo signal. Hope it's not a broken module since i would have to wait a whole month for another one :(

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