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Analogue sensors
Analogue sensors
The diagram shows an HIH3610 Humidity sensor and a Light Dependent Resistor (LDR) both directly connected to ADC inputs of the PICAXE. These are both analogue devices.
Although it would be possible to connect these via the Mux it will probably offer slightly improved accuracy to directly couple them, as the HEF4051 Mux would add a slight resistance between the sensor and the PICAXE input.
The LDR is essentially in a simple potential divider configuration. However when experimenting with an LDR I realised that you can't get sensitivity over the full range of light levels with a fixed series resistor. To overcome this an output of the PICAXE is used to change the series resistance by putting another 4K7 resistor between the LDR and the positive supply when the PICAXE output is turned high. The IN5817 diode is used to activate the resistor only when the PICAXE output is high. This diode has been selected because it's a Schottky diode having a lower forward voltage drop.
The LDR therefore has two operating modes, selectable by the PICAXE. The PICAXE can automatically select the mode that is going to give greatest ADC sensitivity for the current light level.
Unfortunately with this circuit the ADC voltage does not have a linear relationship with light intensity, or Lux. Also, the formulae relating to introducing the 4K7 resistor are quire complex. However they boil down to quite simple expressions for the PICAXE to evaluation. See my article WeatherMonitor Detailed Calculations for more details.
HIH3610 is a Humidity sensor that provides a voltage that is read directly by the PICAXE ADC input.
Although it would be possible to connect these via the Mux it will probably offer slightly improved accuracy to directly couple them, as the HEF4051 Mux would add a slight resistance between the sensor and the PICAXE input.
The LDR is essentially in a simple potential divider configuration. However when experimenting with an LDR I realised that you can't get sensitivity over the full range of light levels with a fixed series resistor. To overcome this an output of the PICAXE is used to change the series resistance by putting another 4K7 resistor between the LDR and the positive supply when the PICAXE output is turned high. The IN5817 diode is used to activate the resistor only when the PICAXE output is high. This diode has been selected because it's a Schottky diode having a lower forward voltage drop.
The LDR therefore has two operating modes, selectable by the PICAXE. The PICAXE can automatically select the mode that is going to give greatest ADC sensitivity for the current light level.
Unfortunately with this circuit the ADC voltage does not have a linear relationship with light intensity, or Lux. Also, the formulae relating to introducing the 4K7 resistor are quire complex. However they boil down to quite simple expressions for the PICAXE to evaluation. See my article WeatherMonitor Detailed Calculations for more details.
HIH3610 is a Humidity sensor that provides a voltage that is read directly by the PICAXE ADC input.
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