Desktop 5 Volt Blue

5 Volt supply for digital (74) projects on the cheap

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Problem: Had no 5 volt supply for my digital logic homework, nor budget to buy one

Solution: Find whatever materials I could around the apartment to make one

Implementation: Harvest USB Cable from broken keyboard, find power/ground on their connector to avoid needless bare wire, secure banana terminal and switch to case, hook up the power to switch/banana, Hook up LED/Resistor to internal banana to indicate power status. Very much like building a ship in a bottle.

Possible upgrades:
Because I kept the usb connector, it still has the data pinouts, these might be utilized for a future project. Possibly upgrade my gaming headphones (also built from scrap parts). Currently uses any USB port or charger, might add some kind of fault protection later.

Needed upgrades:
While I've always been careful about faults, it's been brought to my attention that this circuit needs some form of fault protection such as a fuse or a resettable breaker to be used by anyone else. The breaker idea seems most promising, so if the cost is reasonable I plan to implement that soon-ish. Then, assuming all works well, I'll make a few to keep around the electrical engineering lab. This way future students in the digital series will be able to work on circuits from home as well.

  • 1 × Broken Usb Keyboard Got it free
  • 1 × LED + Resistor
  • 1 × Banana Plug Terminal From an older project that was disassembled years ago
  • 1 × Switch A bit overkill but it was laying around
  • 1 × Plastic Case Pretty sure it was meant for coin collectors, Have a good 20 I use for small parts and screws

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  • 1
    Step 1

    Find an old broken USB component, such as a keyboard or mouse.

    Take it apart and if possible, preserve the connecters to avoid having to solder more than nessisary.

    Find a small plastic container, a pill bottle would likely work fine. If it's sturdy enough, you may want to drill it to save time, but if it was like mine and brittle as hell you'll likely have to use a leather punch or drill bit to do it by hand. Generally, just use common sense, wouldn't want the item you're drilling to shatter and spray sharp plastic shards around the room.

    For my project, I chose to use banana plug terminals, they're cheap and you should be able to get them at most hobby electronic or audio stores. The reason for this choice is twofold: first, it allows you to have pole terminals inside that are easy to access, second, the banana plugs actually unscrew so you can place bare end wires inside and tighten to have a stable connection.

    1. Mark your holes on the container according to your parts
    2. Drill them in, taking care not to make them too big or too small
    3. if your usb cable end has a connector, fit it in first to save hassle later, if not, it can wait. Whenever you pull it through, tie a knot to prevent it from slipping back out, then pull it a bit farther so you have adequate room to work.
    4. Place your connector and switch in the holes you drilled and clean up the edges as neededWire the 5v of the usb to one end of the switch, then the other end of the switch to the banana positive. Goes without saying but you shouldn't have power connected yet
      • wikipedia is a great reference for wiring reference
      • That said, a multimeter works just as well
    5. Wire the ground of the USB to the ground of the banana
    6. Solder the LED and Resistor together and wrap them around the internal poles of the banana terminal. Keep in mind the direction of the LED to current flow. This step may take a bit of time depending on how small your case is and how big your fingers are.
    7. Double check everything is wired properly
    8. Clean up and secure the connections, pulling the usb cable back to the knot you made earlier and placing the lid back in its proper place. A little tidying up goes a long ways.
    9. Connect to a USB charger to test it, flipping the switch to on should suffice, if the LED turns on, you've likely wired it correctly
    10. Build something, 555's and 74 series logic chips are all prime targets here, just make sure to have fun with it.
      NOTE: this setup has no protection, so never plug it in to a computer, always use a spare usb charger on some form of surge protection.

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