Nt1310 Unit 8 Lab Report

The design relied on two Schmitt triggers to generate the two different tones while using the transistors to act as a switch. This causes it to trigger continuously between two unstable states, allowing automatic switching between two frequencies producing two different tones. The RC values between the two Schmitt triggers will differ. Capacitors charge and discharge faster when it’s resistance is smaller. Hence differing capacitor values allows oscillation between the two states. The transistors will act as a switch to toggle between the two inputs. It is a short circuit when turned on and an open circuit when it is switched off. Since only one transistor works at a time, only 1 frequency output will be heard on the speaker at one time.

The design used four of the Schmitt triggers.

3.3.2 Resistors

R1, R2 and R3 – 10kΩ
10kΩ value was used for all three resistors to maintain consistency.
R3 – 1kΩ
The R3 resistor was used as part of the amplifier component. Initially, a 10kΩ resistor was used instead of 1kΩ. However the sound produced from the speaker was too soft. With guidance from the lecturer and student tutors, it was decided that 1kΩ would be used instead of a higher resistance value. The reason for this is simply because of Ohm’s Law. With the voltage set at 3V, a higher resistance will result in a lower current. As explained earlier in the Literature Review, a lower current results in a smaller amplification of sound.

3.3.3 Capacitors

Since the resistor values remained fixed, the capacitor values were manipulated in order to attain the desired frequencies.
C1 – 100uF
The above capacitor is responsible for generating the square wave and the duty cycle.
C2 – 220nF
This value was chosen in order to produce the desired frequency of 570Hz.
C3 – 68nF
The above capacitance produces a desired frequency of 1.838kHz.
These frequencies were chosen in order to emulate the distinct sound of an