Lighting sensors

Purpose

We decided to measure the lighting received by the basket so by the balloon in order to know when they are in front of a cloud. We will be able to study the direct consequence on the temperature inside the balloon. 

The lighting sensor pointed at the horizon because the balloon could have disturbed the measures if it had located on the top of the basket. The sensor is not always in front of the sun because the basket turn. 

Photodiode utilisée : BPW21

Answer's length : 1µs

temperature range: -55°C à 125°C

This diode cost arroud 10 €. It is more sensitive arround 560 nm which corresponds to the maximum of sensitivity of the sun. It works properly and mainly in the visible scope, that is to say between 400 nm and 750 nm. 

Functionning

We used a L.E.D. which is a diode which provides a proportionate current to the received lighting.

We connected it in series with a resistor. As the resistor's volatge is proportionnal to the current (Ohms law), we measured a voltage proportional to the lighting. 

Calibration

To calibrate our sensor, we linked a particular laighting to a specific voltage as following in the below chart.

We acted on the lighting by placing the sensors more ou less far from a white light source. 

(Click on this curve to zoom)