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Cake day: June 13th, 2023

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  • Acid rain is another success story for “making a giant collective change to fix a nearly invisible problem”.

    I think one major difference is that there are enormous companies and entire countries whose way of life truly depends on pumping fossil carbon out of the ground. It wasn’t that way for CFCs or NOx. Sure, Dow/DuPont/whomever surely lost some profitable investment in freon plants, but they had other business as well, and their old customers switched to buying the new refrigerants from the same suppliers.


  • In practice that’s a kind of “no true scotsman” argument though. Libertarians who actually believe in libertarian ideas are really pretty scarce (and I’d say they’re closer to anarchists in thought than most people, though potentially the cool kind of anarchist). Most self-described libertarians either want the government to regulate everyone but them, or they cluelessly take for granted the benefits of the way their world is utterly supported by non-market forces (the house cat analogy).









  • That’s interesting, so you can flip the relays all you like without trouble as long as the 24DC supply isn’t connected? If that’s true then your problem presumably isn’t the typical inductive kick from the relay coil. It looks like your relay board has stuff on it which is presumably drivers and snubbers so let’s assume all of that is adequate to the job.

    So, if it’s inductive kick from the valve solenoid it’s being coupled all the way from there, back through the 24DC supply to the outlet, then forward through the USB supply to your shift register, which is impressive! But not implausible.

    Anyway, three places I’d add some stuff:

    • The main thing you need is a snubber network across the valve solenoid coil itself, ideally physically close to the valve (you want to minimize the area of the loop formed by the valve coil - wiring - snubber). Something as simple as a freewheel/clamping diode would probably help a lot. This will also improve the lifespan of your relay contacts which are probably arcing a little.
    • Small decoupling cap on your breadboard, say 0.1µF on the power supply rails, to keep your logic happy.
    • Larger decoupling cap on your 24VDC rails (the bus on the left), just to eat any transients the snubber doesn’t deal with. Maybe 1-10µF or so?

  • It mostly doesn’t matter.

    If it’s a high-current, high-frequency, or low-noise circuit then maybe the inductance or resistance of those traces would matter, but they’re very short so probably not.

    If you’re mass-producing it, then sometimes the reflow or wave solder process works better if the traces leave the pads in particular ways. You’d talk to your manufacturer about this.

    If this is a hobby project, you’re overthinking it; arrange them in a way that pleases you!





  • In addition to the voltages being different between real-RS232 and “TTL”-serial, they’re also swapped. On a DB9 you probably have something approximating RS232, where mark=-9V and space=+9V, but the debug header is likely mark=+3V and space=0V. So even if your inputs can handle a wide voltage range, the sense is inverted, which is why you’ll get garble.

    (For example, when the line is idle it’s at the ‘mark’ voltage and the receiver knows a character is incoming when it transitions to ‘space’ for one period (the start-bit). If mark and space are swapped, the receiver will see ‘space’ most of the time and only detect a character starting when there are some ‘mark’ bits in the middle of a transmitted character. It’ll never actually synchronize correctly with the transmitter.)

    You can figure out what you’ve got with a multimeter and checking what the voltage is on the TX pin when it’s idle.