Kah Wai@spherebox

Electronic Circuit Design 2

One of my favourite subjects. The lecturer is fun, and the projects are tough but they are exactly what I like to do. Lucky for me, I did not take this subject in my third year (this subject is a third year subject) but I opted to do it this semester as an elective instead. Last year it was taught by another lecturer, one who wasn’t as fun as my current one. Even so, he’s gonna be teaching us for the second half of the semester. You can’t have everything can you? Hehe.

This year, Graeme (my lecturer) had this great idea of giving us a project that we have full control of. Of course, datelines are controlled by him, just that we have free reign on our project design. We were asked to design an audio amplifier with the following specs:

• operate from a single 15V external power supply
• have input impedance > 10k ohms
• have a 3dB frequency response (nominally) 400Hz – 18kHz
• have mid pass-band voltage gain with magnitude of (nominally) 18
• be capable of driving an (external) 68 ohm load with at least 10Vpk-pk
• AC coupled input and output

Following components are available:

• LM741 op-amp + socket
• 2N3904 (NPN BJT)
• 2N3906 (PNP BJT)
• 1N14148 (small signal diode)
• 47 uF 25V elec. Capacitors
• 68 ohm 0.5 W resistor
• PCB pins

After preliminary design on PSpice, a simulation tool for circuits, I managed to build up a circuit that fit the required categories. Actually implementing it on the breadboard gave me lots of grief though. As usual, a lot of things are idealised in simulations, and this ‘idealisation’ sometimes kills the design. After many optimisation processes, I finally am able to construct a circuit that is barely able to meet all required criterias.

After that stage, PCB design came. Implementation was fairly easy (for me) and I handed in my design last Tuesday. The PCB boards came in on the following Monday (technically yesterday since it’s 12.48am for me now) and I completed soldering the thing that day itself. I have not tested it yet though. *Shudder* Knowing the problems that plagued me when I worked on the breadboard, I hate to think the debugging issues associated with this. Ah well, these are the pics of my completed project on PCB.

PCB is missing the op-amp, which is supposed to sit here: (the op-amp is still on my breadboard) – Finger looks fat (check out the PCB size on the next pic)

Size of the PCB as compared to my Sony Ericsson Z800i. For those who haven’t seen the Z800i, the size of the board is 1.95″ x 1.7″. Use a ruler. Small eh?

Now you know what actually sits in those big ass speakers around :) Implementation and design might be slightly different, but the idea is the same.

KW

March 26th, 2007 Posted by Kah Wai at 10:56pm | University Life | 2 comments