Assessment Title: Lab Report - 555 timer with filter

Assessment Task -

You are required to submit a single technical report of a professional standard to satisfy the following requirements.

A company has given you the task to design, simulate and breadboard a 555-timer based pulse-width modulation circuit with subsequent filter stage to the following specification:

Frequency: The 555-timer circuit needs to produce a signal of frequency f = xy kHz where xy are the last two digits of your student ID (if it is '00', the frequency shall be 80 kHz). 

Duty Cycle:  The duty cycle is to be designed such that it is D = (90-xy)/2 % (e.g. for xy = '48' the duty cycle would be (90-48)/2 = 42/2 = 21%). The duty cycle must be a minimum of 5% though, i.e. if D = (90-xy)/2 is smaller than 5%, use D = 5%.

Filter stage: The output of this PWM signal generator then requires filtering. For this purpose, use the second-order cascaded band pass filter shown in figure 1. It is made of a combination of a low-pass filter stage followed by a high-pass filter stage. You are required to calculate suitable component values for R and C such that the above PWM frequency (of 'xy') is selected as the centre frequency of the band pass, thus being the cut-off frequency of each of the filter stages, i.e. use equal values for R_L = R_H as well as C_L = C_H. The gain of the second stage is required to be 10 (i.e. R'_H =10 x R_H).

Design, then simulate, then implement (breadboard) the full circuit. Marks are given for a detailed description of the design and calculation procedure, using circuit diagrams, showing component values and the signals (oscilloscope plots and spectrum analyser plots) for the voltage across the PWM capacitor, V_C, the PWM output signal, V_PWM, and the final filtered signal, V_out. Simulation plots, oscilloscope screenshots and photos of the working breadboard are required for full marks.

Figure 1: The filter stage required to filter the output signal. Component values will have to be determined based on the filter frequency

Report Structure:

-Introduction: Description of the problem

-Design: PWM design

• Give reasons for the specific design presented and used
• Calculation details of frequency, duty cycle, and component values

Filter design

• Calculation of component values

Overall design

• Overall circuit diagram

-Simulation:

• Simulation results including plots of signals (VC, VPWM, Vout) and their frequency spectrums
• Comparison of measured values with theoretical design values (f, D)

-Bread boarding

• Explain selection of component values
• Compare measurement results with simulation
• Briefly analyse graphs and results

-Summary 

• Reflectively summarise your findings (what was unexpected, difficult, etc)

Ensure that any external sources used are cited and referenced in Harvard style.