Week 1

First week summary:

The first week objective focused on the sensor functions achieving, that is, searching for the theorem background to accomplish the conveyor belt functions. Then we simulated the behaviour of each circuit. And decided to use Arduino UNO chip as our functional devices to achieve each functions. In this case, we will not bother calculating the specific relationship between temperature and the consequential speed.

In order to change the speed of the motor depending on the temperature, we decided to use Pulse Width Modulation (PWM) voltage control method in this case.

Pulse width modulation (PWM) is a voltage regulating method that can generate a series of voltage pulses of different duty time so that a varying average voltage will be generated and the speed of the motor will be controlled. For a large duty circle (see right side of figure 1), a higher average voltage will be generated.

Figure 1: PWM control output with different duty time

Theoretically, a 555 timer can be used to generate a voltage pulses with different duty circles. The working time and free time of the outcome pulses can be easily controlled by a pair of parallel variable resistors and capacitor. The simulation result of 555 timer by using Multisim is shown in figure 2. Besides, the diodes shown below works as current rectifier to prevent inverse flowing. 

Figure 2: Multisim schematic and PWM simulation result of 555 timer

It can be shown that a Pulse with a specific duty time can be generated. The active and free time can be calculated as:

$$T_H=0.693(R_1+R_{x1})C$$ $$T_L=0.693(R_2+R_{x2})C$$ $$T=T_H+T_L=0.693(R_A+R_B)C$$
And the consequential voltage becomes:
$$V_{RMS}=V\sqrt{\frac{R_1+R_2}{R_A+R_B}}$$

For a protection circuit, when the temperature goes higher than some critical value, the buzzer should start ringing. In figure 3, the critical voltage for the buzzer is set to be $1.5V$. $R_1$ represents for the thermistor. When the surrounding temperature becomes appr. $50C^{\circ}$, the corresponding resistance becomes 350$\Omega$. In order to trigger the buzzer at this resistance value, the resistance of the constant resistor $R_3$ can be set to be $585\Omega$ and the consequential output voltage around the buzzer becomes $1.508V$.  

Figure 3: Multisim schematic circuit and simulation result for the buzzer alert part

Notes:

A few components were order in this lab session in order to accomplish more functions to the circuit such as alarm and temperature control.

Second weeks objectives:

• Start using Arduino UNO board to achieve the simulation results above. This involves coding and connecting.
• Approval of the component list from Dr.Raja.