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Pew pew pew

Work in Progress
These docs are still a work-in-progress and may not be fully baked just yet! Please contact me if any of it seems very wrong or needs extra clarification.

This is a simple one!

Step(s)​

  1. Solder 220uF capacitor to C1. As always, note polarity. 220uF capacitor on C1

Test​

The beep from before should now drop down in frequency after it starts. Does it sound like a little space laser? RV1 controls its rate of decay.

Testing for a laser sound

Not working as expected? Check the PCB troubleshooting section. Otherwise, continue.

How it works​

Pew pew pew schematic

  • C1 stores voltage from VCC to the oscillator's control input, extending how long the oscillator runs beyond SW2's closure.
  • However, we still have the R1+RV1 pull-down from before. It now drains the cap's voltage to GND, so the oscillator can't run forever.
  • The previously unused pot now controls the speed of that voltage drain.
  • Surprisingly, when the input voltage drops low, the oscillator frequency goes low too. The result is a distinct "laser" sound that starts at a high frequency and then drops low before ending. This is a hack!
    • Logic gates are digital machines. Their inputs and outputs are binary, either high or low. When treated this way, their behavior is as expected. They are in specification, in-spec.
    • If you give them some voltage that's in the middle of VCC and GND, like 3 or 4 volts from the battery's 9v, that is out-of-spec. Manufacturers warn about out-of-spec usages because they can't guarantee how the chip will react. The frequency drop here is almost certainly an unexpected, out-of-spec behavior.
    • Is it good for the chip to be run out-of-spec? Probably not! But it doesn't seem to do it any harm in these short bursts.

Consider:

  • What do you think would happen if we had C1 but without its sibling pulldown/drain resistors?
  • If you have a fast enough multimeter, you could measure the draining voltage at pin 1 of U1A. How does it compare to the frequency drop?

PCB done!​

You're all done soldering the PCB. Turn off your soldering iron and go wash your hands.

If you're up to it, take a minute to read the full, annotated Space Dice schematic. Does it make sense?

Next you'll be putting it together with the 3D-printed parts.