High Sensitivity Vibration Sensor Using Arduino

In my last post I described how to build a High Sensitivity Arduino Sound Level Detector. Another useful type of sensor to determine if something interesting is going on in the environment is a vibration sensor. In this post I use a piezo element as a raw sensor to detect vibration.

I found the raw piezo generated a very small signal. To greatly improve its sensitivity I used epoxy to glue a fishing weight to the piezo sensor. The piezo drives a load resistor of 1M in parallel with a 5.1v Zener diode just to protect the IC's against any large voltage spikes in the event of a large physical bump. I found the raw output of the piezo unsuitable for direct input to the Arduino as it is typically a very small voltage signal and needs amplification, so I amplify the signal from the piezo with a 221 gain non-inverting op-amp using one side of an LM358. I use the other side of the LM358 for a comparator. The sensitivity of the vibration sensor is controlled using a potentiometer for the threshold (negative) input into the comparator. The other (positive) input to the comparator comes from the amplifier of the piezo signal. The output of the comparator provides a direct input to Arduino Uno digital pin 8. To hear when it senses vibration I use a simple piezo buzzer driven directly from Arduino Uno pin 13. Below is the circuit diagram:

... and the breadboard circuit:

Here is the actual prototype:

... and a close up of the piezo element with the fishing weight glued on with epoxy for added sensitivity:

Here is the sketch I used on the Arduino Uno:

If you want to use this as a starting point you can copy / paste from below:

#define VIBRATION_DIGITAL_IN_PIN 8
#define BUZZER_DIGITAL_OUT_PIN 13

int buzzerDurationMillis = 1000;

void setup(){
  pinMode(VIBRATION_DIGITAL_IN_PIN, INPUT);
  pinMode(BUZZER_DIGITAL_OUT_PIN, OUTPUT);
}

void loop(){
    if(digitalRead(VIBRATION_DIGITAL_IN_PIN) == HIGH){
      digitalWrite(BUZZER_DIGITAL_OUT_PIN, HIGH);
      delay(buzzerDurationMillis);
      digitalWrite(BUZZER_DIGITAL_OUT_PIN, LOW);
    }
}

Enjoy. Let me know if you make any cool improvements on this.

Note: if you notice your output locking in on state try lowering the feedback resistor of the op-amp from 220k to something lower, for example 160k.

Update: I later added a 0.1uF capacitor to connect the output from the piezo element to the input of the op-amp, also grounded on the op-amp side using a 100k resistor. This acted as a DC decoupler and effectively lowered the comparator threshold required to detect vibration.

Below is the updated circuit diagram showing the refinements for reducing the gain to avoid op-amp output lockup, and DC decoupler on the input.

If you are wanting to differentiate single bumps from vibrations you may also be interested in this blog I did on an Arduino sketch that can be used to avoid false positives. You may also want to look at my subsequent blog on how to use these in an open door or tailgate down sensor which also uses a Reed switch.

If you are interested in how this type of sensor can be integrated into a broader solution that includes notification of detected vibration on a users Android phone see Detect Intrusion with Passive Infrared, Sound, or Vibration

Follow @davidhoulding

High Sensitivity Arduino Sound Level Detector

Generally we want to sense the environment when something interesting is occurring. Sometimes the presence of sound is indicative of an interesting activity. If we can detect sound level we can trigger a sensing activity to capture information about the activity of interest. I have posted a short video of this simple high sensitivity Arduino sound level detector working.

In this project we use an Arduino Uno, an electret microphone and an LM358 dual operational amplifier to create a simple sound level detector. The signal from the mic is amplified by the one side of the LM358 with a gain of approximately 221 (see op-amp wiki) as defined by the 220k feedback resistor and the 1k pull down resistor connected to the negative input of the LM258 amplifier. The output of the first stage amplifier provides input to the other side of the LM358 used as a comparator. The triggering threshold of the comparator is controlled using the potentiometer. When the audio signal from the first amp exceeds the triggering threshold the comparator sends a digital '1' to the Arduino Uno on pin 8. When the Uno detects the sound level high input it turns an LED on. You can see a schematic diagram of the sound detection part of the circuit below.

Prototyping this on a breadboard looks something like this:

The actual breadboard prototype appears below:

... and the simple sketch I used to drive the Arduino Uno appears below:

I include the sketch code below if you'd like to try it out yourself:

#define SOUND_DETECTED_DIGITAL_IN_PIN 8
#define LED_DIGITAL_OUT_PIN 7

void setup(){
  pinMode(SOUND_DETECTED_DIGITAL_IN_PIN, INPUT);
  pinMode(LED_DIGITAL_OUT_PIN, OUTPUT);
}

void loop(){
  if(digitalRead(SOUND_DETECTED_DIGITAL_IN_PIN) == HIGH){
    digitalWrite(LED_DIGITAL_OUT_PIN, HIGH);
    delay(50); // delay long enough for you to see the LED on
  }
  else {
    digitalWrite(LED_DIGITAL_OUT_PIN, LOW);
  }
}

Stay tuned for projects that receive the sound detection as input and use it to drive other interesting activities. Have fun. Feel free to share below if you built something cool with this, or have some ideas for enhancements.

You may also be interested in a high sensitivity vibration sensor using the Arduino Uno.

Note: if you notice your output locking in on state try lowering the feedback resistor of the op-amp from 220k to something lower, for example 160k.

If you are interested in how this type of sensor can be integrated into a broader solution that includes notification of detected sound level on a users Android phone see Detect Intrusion with Passive Infrared, Sound, or Vibration

Follow @davidhoulding