Task 6C

Points: 150

The Case of the Four Signals

Prologue

It was a dreary Thursday evening at 221B Baker Street when Inspector Lestrade arrived, visibly flustered, clutching a leather satchel. He laid before Holmes the remnants of a curious apparatus, a partially burnt circuit board recovered from the den of Professor Alistair Voss, a disgraced electrical engineer suspected of orchestrating a string of telecommunications frauds across London.

“The device,” Holmes said, lifting a fragment to the gaslight, “was a signal routing machine. Voss was feeding four distinct analog signals into a selector, intercepting whichever channel he wished at the turn of a jumper. Elegant. Criminal, but elegant.”

He turned to you, eyes sharp.

“Scotland Yard needs this device reconstructed, fully documented, fully functional. Can you do it?”

The Assignment

You are tasked with reconstructing Professor Voss’s signal routing apparatus from first principles.

The device comprised two sections:

Part I: The Four Signal Sources

Voss’s machine generated four analog signals, each processed by a dedicated circuit built around an operational amplifier. You must implement all four independently:

Signal Circuit
Signal A Summing Amplifier: adds two input voltages
Signal B Difference Amplifier: subtracts one input from another
Signal C Ideal Integrator: outputs the time-integral of an input
Signal D Ideal Differentiator: outputs the rate of change of an input

All four circuits must be designed independently, each as a self-contained op-amp stage.

The output equations for each circuit, along with the component value constraints, are detailed in the attached reference sheet. Use these to determine appropriate resistor and capacitor values for your design.

Part II: The Selector Mechanism

The outputs of all four circuits fed into a 4:1 multiplexer, Voss’s method of switching between intercepted channels at will.

Holmes’s analysis of the charred remains revealed that Voss had built his selector to handle the analog nature of the signals cleanly, routing waveforms without distortion or loss. The select lines, Voss’s channel keys, were implemented using push buttons, allowing silent toggling between the four feeds at will.

You must do the same. The 4:1 analog multiplexer must be constructed to faithfully pass the op-amp outputs, with the select lines controlled by push buttons.

Holmes’s Directive

“A case is only as strong as its documentation, Watson. I will not accept loose wiring and vague labels. Every component named. Every signal traced. The schematic drawn cleanly in KiCAD, for it may one day be presented as evidence.”

Your schematic must reflect:

You may use the following ICs or any other as per your preference:

Resources

Op Amp:

MUX:

KiCAD:

Closing Note from Holmes

“You have all the clues. The question is whether you have the intellect to assemble them.”

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