Electronics
This project uses a Raspberry Pi as a central computer with added electronics designed to process the generated voltage input and output the PWM signal.
The input generated voltage from the DC Motor is really small (in the mV range). Therefore, an op-amp (Operational Amplifier) is added to amplify the signal. The Raspberry Pi does not read analog input signals, thus a 12-bit ADC (Analogue-to-Digital Converter) with 4 channels (ADS1015) is used to read the input voltage signal using the I2C communication bus. Depending on the input voltage readings obtained from the generator, a Pulse-Width-Modulation (PWM) control signal is sent to the servo motor which controls the blade pitch. This is done to keep the generator within proper operating limits.
The specifications of ADS1015 which has been chosen to convert signal will be provided in the table 1.
Table 1: Specifications of ADS1015 and the recommendded operating conditions
| Feature | Pins | Min/Reccommendded | Max/Reccommendded | Unit |
|---|---|---|---|---|
| Power-supply voltage | VDD to GND | -3 / 2 | 7 / 5.5 | V |
| Analog input voltage | AIN0, AIN1, AIN2, AIN3 | GND-0.3 / ±0.256 | VDD+0.3 / ±6.144 | V |
| Digital input voltage | SDA, SCL, ADDR, ALERT/RDY | GND-0.3 / GND | 5.5 / 5.5 | V |
| Input current, continuous | Any pin ecept power supply pins | -10 | 10 | mA |
(Adapted from TEXAS INSTRUMENTS)
At first ADS1015 was expected to receive analog voltage alone from the wind turbine model which is quite small, however, the result after it has been tested is not as the expectation. Therefore, it requires an amplifier which could increase the signal, LM324 which is provided by the university has been chosen for this circuit.