## 2 Materials and Methods
### Materials, Design, and Construction Method
#### 2.1.2 System Components  
* The frame was made of a 30 mm \(\times\) 30 mm steel profile, as shown in Figure 2.
* The reservoir kept and stored the hazelnuts. The reservoir outlet was designed and made in such a way that it prevented nuts from accumulating on a rolling distributor and allowed them to move in a single row. In addition, the distance of the reservoir outlet was equal to the highest diameter of the biggest hazelnut. * An acoustic chamber was designed to avoid the effects of external noise (Figure 4). Sound insulating materials (Isoham insulation) were used in the interior chamber structure. The microphone was placed about 5 mm below the disk. An acoustic chamber was placed on a hinge joint so that the desired angle could be adjusted. This prevented the hazelnuts from moving outside due to collision with the disk. Since the distance between the distributor and the acoustic chamber affected the quality of the signal received by hazelnuts, the platform jack was used to change this distance to optimize the received signals. * One of the most important parts of the system is where hazelnuts were transferred and graded individually. Thus, a rolling distributor was used, which is simple and inexpensive, to receive hazelnuts individually from the reservoir and transfers them to the outlet (Figure 5). \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Length** & **Width** & **Thickness** & **Mean** \\ \hline Large(a) & 20.53 mm & 19.35 mm & 17.80 mm & 19.23 mm \\ Small(b) & 16.24 mm & 16.21 mm & 14.78 mm & 15.75 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean dimensions of 100 samples of each group of hazelnuts. Figure 4: Acoustic chamber. Figure 5: Rolling distributor and coating. After determining the hazelnut dimensions, the size of the holes in the rolling distributor was set to 24 mm, which is equal to the diameter of the largest hazelnut. A rolling distributor with a 130 mm diameter and 38 mm thickness was made from Teflon. This setup held only one hazelnut inside the hole. The hazelnuts sitting on the holes are led toward the outlet where it comes out onto the intended surface. Figure 6a shows the complete housing. The nut holder, as shown in Figure 6b, contains a rolling distributor and acts as a pullover edge. If more than one hazelnut passes this point, other hazelnuts are slipped to the side and will move upward. Another critical parameter is the tolerance of distance between the rolling distributor and its housing, so that both large and small hazelnuts can go through the distributor. To achieve this purpose, the dimensions of hazelnuts were measured, and the tolerance was determined to be about 10 mm. In order to rotate the rolling distributor, a 12 V electric motor equipped with a gearbox was used to turn the rolling distributor through a shaft. One of the essential parameters in the selection of the electric motor was its rotational speed (speed: 40-55 rpm; voltage consumed: 12 V; torque lock: 20-30 Nm; engine power: 55-100 w). Motor speed can be controlled using pulse generation using a timer-integrated chip (555, NXP Semiconductor, 565 AE EINDHOVEN, Netherlands). If the rotational speed of the electric motor is high, the hazelnut will stick between pullover edge and rolling distributor holes. Besides, high speed does not give enough time to the rolling distributor to be completely filled. Therefore, a gearbox electric motor with a maximum speed of 40 rpm was used. * The components of the audio circuit are shown in Figure 7a,b. The audio signal circuit provides microphone connectivity to the sound card of the computer. The sampling input rate of audio signal was 44,100 times per second (44.1 kHz), with16-bit accuracy in a maximum range of -1 to +1 volts. Due to the impact of the hazelnut on the metal disk, which is located on the upper surface of the acoustic chamber, the computer program was activated, and time was taken for the verification of the impact by the microcontroller.