The latest issue of Circuit Cellar has an article about a Dew Point Monitor that would make a good add-on for all those PICAXE based weather stations out there.
Briefly, the dew point is the temperature at which air must be cooled, at constant pressure, so that it will be saturated with respect to water. It would seem that this is an important parameter for meteorology, farming and many chemical processes.
The instrument described by Peter Gibbs & Ramon Sargeant uses a Peltier device to cool a DS1620 temperature sensor that has reflexive tape stuck on its surface. An IR beam is bounced off this ‘mirror’ and the light level monitored by a microcontroller's ADC.
A simple measurement sequence is as follows; the microcontroller drives the Peltier device (via PWM) to cool the sensor until the reflected light level drops sharply as a result of dew forming on the mirror. The temperature of the sensor is then read by the micro, to give the Dew Point, and the cooler switched off.
The hardware looks pretty straightforward and there are no critical timing issues for the software. Should therefore make an interesting hobby/educational PICAXE project.
Briefly, the dew point is the temperature at which air must be cooled, at constant pressure, so that it will be saturated with respect to water. It would seem that this is an important parameter for meteorology, farming and many chemical processes.
The instrument described by Peter Gibbs & Ramon Sargeant uses a Peltier device to cool a DS1620 temperature sensor that has reflexive tape stuck on its surface. An IR beam is bounced off this ‘mirror’ and the light level monitored by a microcontroller's ADC.
A simple measurement sequence is as follows; the microcontroller drives the Peltier device (via PWM) to cool the sensor until the reflected light level drops sharply as a result of dew forming on the mirror. The temperature of the sensor is then read by the micro, to give the Dew Point, and the cooler switched off.
The hardware looks pretty straightforward and there are no critical timing issues for the software. Should therefore make an interesting hobby/educational PICAXE project.