Group Task

Input Devices

The assignment for the output device was measuring the analog levels and digital signals in an input device. For analog we chose to measure the levels of a photoresistor. For the digital one we chose to use a button.

Photoresistor

A photoresistor is a small sensor with variable resistance depending on intensity of light falling on the sensor. Svetlana will use this in her final project. However, an AVR is not directly capable of measuring resistance. In order to use the sensor it has to be used as part of a voltage divider that will be monitored using the analog-digital-converter of the AVR.

As a first test for this we hooked up the photoresistor in series with a 1k ohm resistor and applied 5V to it. Then we measured the voltage on the photoresistor for different light exposures.
We found that the resistance lowers with increasing intensity and we observed the voltage on the photoresistor lowering down to ~300mV. Covering the sensor increases the resistance and the measured voltage climbed to ~800mV.

Schematic of our test setup.

Voltage of a photoresistor that does not capture light.

Voltage of a photoresistor that captures light.


Button

Resistance of pushed button.

Resistance of unpushed button.



Output Devices

The assignment for the output device was measuring the power consumption of an output device. We decided to measure two different devices.

LED

Speaker