1) TEMPERATURE SENSOR
The temperature sensor measures the temperature in
the greenhouse. It is connected to a 5V power supply with a current limiting
resistor. This limits the current to the allowable operating current of the
sensor, which is between 6µA and 12µA. We chose the average resistance to
guarantee the efficiency of the circuit. The sensor’s output is connected
directly to the PIC. The current output of the sensor is 100µA with an output
voltage ranging from 0V to 1V. Since this current output is less than the
maximum current input of the PIC (25mA), a direct connection is possible. To
convert the output voltage to the equivalent temperature measurement, the
datasheet provides the necessary equations. The equation is as follows:
TA = V out - V°C
TC
Where: VOUT = Sensor Output Voltage
TC = Temperature Coefficient (10.0mV/°C)
TA
= Ambient Temperature
V0°C
= Voltage at 0°C (500mV)
2) LIGHT DEPENDENT RESISTOR (LDR) SENSOR
The LDR
light sensor detects the light intensity shinning into the greenhouse. The
output of the sensor will be in analogue ranging from 0 to 1V. Since the PIC’s
maximum input current is 25mA, we set the sensor’s output current to be 20mA
for extra precautionary measures. Ohm’s law was used to determine the
resistance needed to limit the current at this voltage output range.
Ohm’s Law: Voltage [V]
= Current [A] x Resistance [Ω]
3) HUMIDITY SENSOR
The
humidity sensor is used to determine the relative humidity level inside the
greenhouse. It requires a 5V power supply and can be directly connected to VCC.
The output of the sensor ranges from 0V to 1V. To determine the equivalent
relative humidity, the voltage output will be analyzed. As stated in the
datasheet, the voltage output varies linearly with the humidity level - every
0.01V is equivalent to 1%RH. This is a very useful feature of the sensor as it
helps determine the humidity level faster and more efficiently.
