Electric Soup

Vikash Mansinghka, Mark Feldmeier

SOLUTION:

• Stare at the circuit in terror
• Get a grip; begin coping. Unless you're C Scott, in which case suffer some more first.
• Realise the circuit's divided into five sections:
• Timing logic (first chunk; resistor ladder feeding gates and comparators)
• Suspiciously audio-like output stage (mixer, output driver)
• RF component (fixed tuning)
• Hairy digital logic
• possibly vco like circuit
• Begin circuit analysis, hopefully ignoring details of timing and output stages for now.
• RF part: realise antenna is tuned to NIST broadcast. Look it up on google. Find that it broadcasts 440 hz. Realise this is an "A".
• VCO part: realise the two current sources fight each other as triggered by the comparator to produce a sawtooth wave at times 3, 4, 6 (see below). Do analysis on cap values and current sources to determine frequencies which are E and F (or at least their associated frequencies; if you've seen the suspicious 440hz, hopefully get the pitches, again from google). Note that Vbe is .6V at the level of current drawn by the circuit; this can be obtained by checking the datasheet.
• Digital part: discover crystal is an oscillator at 4.9152 mhz. Discover basic unit is a JK flip-flop, and that the two paths through the logic frequency divide the oscillator by 2^13 and by 9600, yielding frequencies 512 and 600hz, which are closest to C and D. (Use flavortext to ignore accidentals.)
• Figure out the notes, in order, are: A C D E E D F
• Figure out flavortext of taking six steps forward means raise six half steps, yielding E G A B B A C
• Figure out flavortext of flipping the diagram means reverse, yielding CABBAGE
• Notice that this puzzle is about groceries. Be happy with the answer.
```0  1  2  3  4  5  6
C  A  B  B  A  G  E
E  G  A  B  B  A  C
Eb Gb Ab Bb Bb Ab B
D  F  G  A  A  G  Bb
Db E  Gb Ab Ab Gb A
C  Eb F  G  G  F  Ab
B  D  E  Gb Gb E  G
Bb Db Eb F  F  Eb Gb
A  C  D  E  E  D  F
```