Team:Cornell/project/drylab/components/electronics

Due to the nature of our project, the most important feedback control loop to be implemented was the heating circuit, and so it was given priority. The heating circuit consists of a transistor to switch the heating element (power resistors) on and off, along with a 12 volt power supply to provide enough voltage to heat the resistors to the required temperature (about 30°C). Also, the feedback from the circuit is provided by a an analog LM34 Fahrenheit temperature sensor which connects directly to the arduino.

The second feedback loop which is currently being worked on is a humidity control circuit. The HH10D relative humidity sensor module is being used to collect data in order to adjust the environment.

Temperature Sensor and Heating Element Circuit:

The Heating Circuit is illustrated below:
The components used are listed below:

• LM34 temperature sensor
• F12N10L transistor
• 10W(8Ω2J) power resistors-XICON
• 12V max variable power supply
• F12N10L transistor
• 10kΩ resistor

The temperature sensor is hooked onto the A1 port of the micro-controller to allow the micro-controller to read data from the sensor. The micro-controller was programmed in C through the Arduino IDE to read the temperature every second. The program is designed as a feedback loop which decides whether to raise or lower the temperature based on the temperature input. Temperature is controlled by switching on or off the power loop. The micro-controller outputs a certain voltage based on the program, and that voltage (0 or 3.3V) will signal the transistor to switch on or off, either opening or closing the 6 V loop, which heats up the whole tank.

The LM34 temperature sensor was chosen because it can read a wide range of temperatures to a 1.0°F accuracy, which is perfect for tuning the temperature of the incubator. Once the entire circuit was hooked up with the right components according to the schematic, measurements were taken to compare the temperature sensor with an actual thermometer’s readings. The temperature sensor was accurate to within 1°C, which was one of the requirements for the mushroom incubator. During the calibration, the temperature sensor reacted a lot quicker to temperature change than the actual thermometer. While the sensor and the thermometer were not placed in the same location by the resistor, they were close enough for this difference to be negligible. While doing this calibration, the change in voltage was recorded on the oscilloscope. Refer to the two diagrams in the Heating Circuit section to see the different options for heating by adjusting the duty cycle of the high to low voltage ratio.

Humidity Sensor:

A HH10D humidity sensor module was used to measure the relative humidity of the environment. This sensor was connected according to manufacturer instructions such as connecting power, ground, frequency output, SCL, and SDA to the corresponding pins on the sensor board.

To collect data about the humidity, a mistmaker was used to increase the relative humidity of the surrounding area, and the humidity sensor was placed in the vicinity of this mistmaker from the start. This experiment was done by putting the mistmaker in a box, making sure to not allow the mist to escape, and as the mistmaker distributed the water more evenly throughout the box, the relative humidity increased. As the amount of humidity began to increase, the sensor could measure the increase in relative humidity.

The components used are listed below:

• HH10D Humidity Sensor
• Ocean Mist Mist Maker, DK-24
• 5.1kΩ Resistors (x2)