• 1 Post
  • 74 Comments
Joined 2 years ago
Cake day: July 19th, 2023
  • Ulvain@sh.itjust.worksOPtoAsklemmy@lemmy.ml•Asking plumbers on lemmy: is this ok?
    24·
    4 months ago

    UPDATE thanks all for the comments, just a few clarifications and updates:

    • all electrical work is work-in-progress, we’re finishing it up tomorrow, it’s still an active worksite. The old outlet and old bx wiring is being removed, we’ll only have the newer wiring (and of course all outletd will be in their gangboxes and covers will be on)

    • the dryer vent will be changed and installed without sag when we finalize

    • the 4" abs drain connects to the old one with a rubber fernco gasket, those do require hose clamps and they’re up to code (though the top clamp could be straightened!)

    • the water lines are pex, they’re all good

    • we don’t have a choice but to push the water up with the washer pump - the drain evacuates to the city sewer around hip level in that basement

    The worries for me are really the 90° out of the sump pump and the other 90° into the drain column, shouldn’t that be a downward Y? And the double S p-trap, is it creating some risk?

  • Ulvain@sh.itjust.workstoShowerthoughts@lemmy.world•I wonder what the specs are on the technology that disables shopping cart wheels
    722·
    5 months ago

    This might actually be a good opportunity for an AI answer:

    –

    First, understand the basic principle you’re working with:

    Shopping cart wheel locks respond to a specific RF (radio frequency) signal (typically around 7.8 kHz to 10 kHz for many systems, but it varies by brand).

    In normal operation, the boundary wire emits this signal constantly.

    The unlocking posts emit a different coded signal to reset the wheel.

    So to design a portable device that could lock and unlock wheels manually anywhere, you would need:

    1. Identify the Signals

    You must figure out the exact frequencies and modulation patterns used by the cart system.

    Different companies (like Gatekeeper Systems, Carttronics, etc.) use slightly different RF signatures.

    Usually lock signal = basic broadcast (constant tone) Unlock signal = special modulated unlock code or sequence.

    This might require:

    A spectrum analyzer

    Or reverse-engineering an existing unlock station.

    1. Design the Portable Emitter

    The portable device needs:

    A programmable low-frequency RF transmitter (around 8–10 kHz range, low power)

    A microcontroller (Arduino, ESP32, etc.) to generate the right modulation if the signal is coded

    An amplifier to make the signal strong enough to reach the cart wheels (they usually detect it within 3–10 feet)

    Optionally:

    Two modes: a “lock” mode (sending the boundary signal) and an “unlock” mode (sending the unlock code).

    1. Basic Hardware Components

    Low-frequency oscillator (to generate 7.8–10 kHz wave)

    Microcontroller (to handle switching, coding)

    Coil antenna (for strong near-field transmission — like a small induction coil)

    Amplifier circuit (boost the signal so carts sense it a few meters away)

    Battery pack (portable, rechargeable — say 12V lithium-ion)

    Mode selector switch (Lock / Unlock)

    1. Software

    Simple microcontroller code to:

    Emit plain carrier signal = Lock mode

    Emit modulated code = Unlock mode

    Example (pseudo-Arduino code):

    if (mode == LOCK) { generateContinuousTone(8kHz); } else if (mode == UNLOCK) { generateUnlockCode(); }

    1. Important Challenges

    Matching signal format exactly: If the unlock signal is digitally modulated (like FSK or ASK), you must match the timing perfectly.

    Power levels: Too much power could fry circuits or interfere with nearby electronics. Keeping it safe is key.

    Legal considerations: Broadcasting radio signals, even low-power ones, can be restricted depending on the country.

    Simple Concept Sketch:

    [Portable RF Cart Lock/Unlock Device]

    Size: About a large walkie-talkie

    Two buttons: Lock / Unlock

    Coil antenna: About 3–6 inches

    Range: 1–3 meters effective

    Display: Small LED indicators (Locking / Unlocking / Signal OK)

    In short: You’re essentially building a portable invisible “fence” generator with two channels: a “keep away” signal (lock) and a “come back” signal (unlock).