To control the solenoid motors, we elected to use optoisolators. The control pins of the MCU were attached to the optoisolators which turns on and off the solenoid by controlling a TIP31 transistor. The TIP31 serves as an on/off switch for the solenoid. The optoisolators (4N35) were needed so that the MCU was completely isolated from the circuit. This protected the MCU because there were no physical connection between the MCU and the power supply. The 4N35 works by using a phototransistor that senses LEDS when the device is turned on.
The sensors were measured by a voltage division circuit coupled with an operational amplifier to achieve the desired results. The voltage outputted from the sensors was sent to the ADC of the MCU. The reference voltage of the MCU ADC was set to 5.0 volts which would correspond to the digital value 255 since only the top 8 bits of the ADC were used. We simply used this digital value to determine exactly how much juice we have dispensed.
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