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Waspmote Oxygen Sensor

Quick Data

  • Model: Figaro Oxygen Sensor SK-25F
  • Measurement range: 0 ~ 30%
  • Output Range: 0-10mV
  • Gain Applied to Output: 100
  • Standard Conditions: 5.5 - 8.8mV at 21% O2 concentration
  • Some approximate oxygen levels for reference
    • Atmosphere: 20.95%
    • Cretaceous-period air 25-35%
    • Basement: 19.2%
    • Pressurised Aircraft: 17%

Conversion Methods

Method 1: See if oxygen lies within an expected range (no calibration required)

The output of the sensors have a gain of 100 applied to them (Allowing better resolution from the ADC). This gain is also present in the database readings, and stored in Volts. So simply take database results, divide by 100 to remove gain, multiply by 1000 to convert to millivolts, and if the reading falls between 5.5 and 8.5 mV we can assume normal concentration.

Oxygen concentration is normal if 5.5mv < ( reading in mV / 100) < 8.8mv

See the red dotted lines below indicate the upper (8.8mv) and lower (5.5mV) expected readings for a 21% oxygen level. The readings show a well ventilated room. Readings in the basement would tend towards the lower limit, if not exceed them.

Method 2: Converting to Concentration of Oxygen in Air (%) (calibration required)

  1. Convert voltage reading from database to millivolts
  2. Adjust to compensate for gain (divide reading by gain magnitude)
  3. Compare against sensor response graph (or use provided linear equation)

Sensor Response Characteristics

Output Voltage (mV) to Oxygen Concentration (%)
O2 (%) = (Vout - 0.45) / 0.318


Measurement of 0.72v is observed (from our databases)

  • 0.72v = 720mv
  • Adjust for gain: mVout = 720 / 100 = 7.2mV
  • Compare 7.2mV against sensor response graph of linear equation to approximate concentration
  • Concentration = (7.2 - 0.4) / 0.318 = 21.23% which is very close to expected atmospheric concentration (well ventilated room)


  • Keep in mind these readings only approximations. Results will vary from one sensor to another and between differing atmospheric pressure, temperature and humidity. Sensors can be calibrated against others and the offsets applied for more accurate readings.


wasp_o2.txt · Last modified: 2021/01/10 23:16 (external edit)