I connected my ADXL1002 to Teensy4.1 using Arduino IDE, but struggling with g

Projects General Guidance
1

ADXL1002 is a 50g single axis accelerometer and I connected it to the analog pin of teensy4.1 which has 12-bits ADC.

When the accelerometer is placed flat , I got maximum of 2119 raw value, when tilt to the left ,I got 2049, tilt to the right ,I got 2049 and when upside down I got 2119.

With the code below , how can I get acceleration in g, and in m/s^2.

When using it for vibration analysis, which unit will be easy to play with when FFT and PSD etc are needed.

#include <ADC.h>

#define ADXL1002_PIN A17
#define ZERO_G_VOLTAGE 1.65 // in volts 0g offset
#define SENSITIVITY 40 // in millivolts/g
#define ADXL1002_SAMPLING_RATE	1   //us --> 1 Msps ??

ADC *adc = new ADC();
int adxl1002_value = 0;
elapsedMicros sinceLastSample; // timer for sampling
const uint32_t samplingIntervalUs = 1; // sampling interval in microseconds



void setup() {
  Serial.begin(2000000);



  adc->adc0->setAveraging(16); // set number of averages
  adc->adc0->setResolution(12); // set bits of resolution
  adc->adc0->setConversionSpeed(ADC_CONVERSION_SPEED::VERY_HIGH_SPEED); // change the conversion speed
  adc->adc0->setSamplingSpeed(ADC_SAMPLING_SPEED::VERY_HIGH_SPEED); // change the sampling speed
  sinceLastSample = 0;
}

void loop() {
  //if (sinceLastSample >= samplingIntervalUs) {
    //sinceLastSample = 0; // reset the timer
    int rawValue = adc->analogRead(ADXL1002_PIN);
    
     Serial.println(rawValue);

    delayMicroseconds(100);
 // }
}
2

Patiently waiting for response

3

Convert your ADC reading to a voltage and use pages 10 and 11 of the sensor datasheet to create an equation that gives the acceleration.

4

Thanks for your response.

I have looked at the recommended pages . The output voltage is ratiometeric , since I am using 3.3V the sensitivity is 26mV/g

Take one of the raw values , say 2117, for analysis

Calculate acceleration in g-force:
g = (Raw Value - Zero g Value) / Sensitivity
g = (2117 - 1.65) / (0.026)
g = 80.115 g

Convert acceleration from g to m/s²:
Acceleration in m/s² = g × 9.81
Acceleration in m/s² = 80.115 × 9.81
Acceleration in m/s² ≈ 785.935 m/s²

Calculate voltage:
Voltage Step Size = Reference Voltage / (2^Resolution)
Voltage Step Size = 3.3 V / (2^12)
Voltage Step Size ≈ 0.000805664 V
Voltage = (Raw Value / (2^Resolution)) * Reference Voltage
Voltage = (2117 / (2^12)) * 3.3
Voltage ≈ 1.0142 V

I don’t know if I am right?

5

A reading of 2117 is 69 steps above the theoretical zero G 2048 mid point.
69 steps = 55.5mV or approx 2G which seems reasonable as you have a combination of earth's gravity plus noise, vibration and measurement error.

6

Thanks again for your response.

Is there something I am not doing right?

The setup is for vibration analysis and high precision is needed.

7

Do you have calibrated test equipment that can be used to calibrate your sensor and Teensy combination?

Is the Teensy rated for a 50G environment? If there is a measurable ambient magnetic field then all conductors including the sensor wires will act as a dynamos generating voltages that will interfere with your millivolt readings. If this is a student project perhaps your supervisor wants you to discover and quantify these measurement errors.

8

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