5 ms·

I would be using PLCs and RS485 for this project. I can't figure out exactly how many IOs they'd need per cubicle (I guess 3 buttons, 2 LED colors) but I'd figu

I would be using PLCs and RS485 for this project. I can't figure out exactly how many IOs they'd need per cubicle (I guess 3 buttons, 2 LED colors) but I'd figure you could use one PLC for maybe 6 boxes... I have to say, much like you, I am finding the 'debounce is an incredibly nuanced thing to implement' commenting to be... odd... The 1-100 video reminds me a lot of that 'climbing for dollars' bit from The Running Man, so, you know, maybe it's a good thing they find debounce an incredibly hard concept to master. Off to the supermarket now to buy mouthwash!

geerlingguy 3y ago
In the blog post I mention using RS485 (or CANBUS) instead of the solution we went with, but on a 5 day timeline, and building on a set where I wouldn't be present (initially I was not planning on being there at all during the shoot), I didn't want to put in a solution someone else on staff couldn't at least wrap their mind around. In hindsight... there's always a lot that can be done different :) And regarding the debounce—I don't mention this in the video explicitly (for time), but there were three other 'modes' for the buttons that were implemented that were never ultimately used, for games like Simon (press colors to match a pattern), and timing-based games, so the debounce was actually critical to allow varying ages to press buttons sometimes in tandem and sometimes in sequence with certain timings. Because of the issues we had (not the least of which was a weird bit of a drain on the 3.3v as you held down a button), I recommended against some of the challenge types. In the end, the only things that made it to the final cut of the 1-100 video was the 'yes or no' style votes on a challenge. Which, yes, are incredibly easy to debounce. Lock in the first button press and you're done ;)
- 15457345234 3y ago
  > weird bit of a drain on the 3.3v Yeah, 3.3v isn't really viable as a signalling voltage for anything that leaves an enclosure unless you take steps to mitigate interference such as differential signalling, shielded cable or some sort of protocol rather than presence/absence of voltage. It's just too easy to induce that voltage - albeit very temporarily - through capacitive or inductive coupling on even 10m of wire; as you experienced it's also too easy to have that voltage mysteriously leak out into what a multimeter will tell you is a definitively open circuit. If you're thinking of doing something like this again, I'd suggest: 1. Definitely use PLCs, their inputs are inherently hardened and you can use 24/48/240v signalling voltages - and by extension a whole universe of very robust industrial indicators and switches. 2. Don't use data cable for non-data transmission, the twisted pair coupling will give you issues you don't want and the stuff is fragile as anything. If you want a good cable which supports multiple non-data channels the term 'pilot cable' or 'control cable' will see you right, that's a multi-core cable which usually has 4 thick cores and a bunch of thin pairs, it's traditionally used for carrying 4-20ma signalling loops in factories and oil rigs etc, it's well shielded. 3. Do use RS485 to loop your PLCs together. 4. Don't use weak voltages on stuff that's being handmade and screwed together onsite. You run into all sorts of transient issues, 3.3v will balk at a loose terminal whereas 48v will romp home if there's even a hint of contact.
  - geerlingguy 3y ago
    That was what my Dad mentioned too—he's built a lot of signaling systems for tower sites and radio studios and was nervous about me running 3.3v over any length of Ethernet. But he assumed we'd have shielded Cat5e at least... that would've helped somewhat.
    - 15457345234 3y ago
      Either pullup or pulldown resistors would have helped - you see this a lot in PCB design, even short traces that are used for signalling will be pulled low or high via a relatively high resistance. That ensures that you have a sharp transition when the switch or whatever is closed or opened and that a floating voltage can't appear over time on your line and cause false triggers.
- ilyt 3y ago
  There are modules where you just have ethernet and few IO ports, for example WISE-40X0LAN series. It's pretty much what you've built but industralized. And, as it is for industrial stuff, pretty pricy, 150 EUR a pop. But works with via both HTTP and MQTT
- numpad0 3y ago
  > weird bit of a drain on the 3.3v You...had current limiting resistors in series for each buttons, right? edit: I think each buttons could be made to register the last pressed UNIX time rather than sending out button event, so the host can collect reports and sort out time sensitive aspects "later" in the loop to account for delays and reordering type of issues
  - 15457345234 3y ago
    How much accuracy do you want? Now you have issues syncing all the SBCs to a timeserver and how much drift their internal clocks have. Some of those things have very vague timing. If timing is critical I'd run all the buttons back to a dedicated device but where you'd find a PLC-alike with 200 inputs polled 'simultaneously' (FSVO simultaneously) I don't entirely know. This is the type of project where very particular issues become annoyingly apparent only after you've chosen a hardware platform.
    - geerlingguy 3y ago
      Quite true. And a few of the hard requirements became a bit softer after we got on-site and ran into the issues that couldn't be solved for lack of time.
    - numpad0 3y ago
      I was thinking more along that rate limit might not be high enough with industrial stuffs, they generally don't like e.g. polling at 125Hz.

geerlingguy 3y ago

In the blog post I mention using RS485 (or CANBUS) instead of the solution we went with, but on a 5 day timeline, and building on a set where I wouldn't be present (initially I was not planning on being there at all during the shoot), I didn't want to put in a solution someone else on staff couldn't at least wrap their mind around. In hindsight... there's always a lot that can be done different :) And regarding the debounce—I don't mention this in the video explicitly (for time), but there were three other 'modes' for the buttons that were implemented that were never ultimately used, for games like Simon (press colors to match a pattern), and timing-based games, so the debounce was actually critical to allow varying ages to press buttons sometimes in tandem and sometimes in sequence with certain timings. Because of the issues we had (not the least of which was a weird bit of a drain on the 3.3v as you held down a button), I recommended against some of the challenge types. In the end, the only things that made it to the final cut of the 1-100 video was the 'yes or no' style votes on a challenge. Which, yes, are incredibly easy to debounce. Lock in the first button press and you're done ;)

15457345234 3y ago
> weird bit of a drain on the 3.3v Yeah, 3.3v isn't really viable as a signalling voltage for anything that leaves an enclosure unless you take steps to mitigate interference such as differential signalling, shielded cable or some sort of protocol rather than presence/absence of voltage. It's just too easy to induce that voltage - albeit very temporarily - through capacitive or inductive coupling on even 10m of wire; as you experienced it's also too easy to have that voltage mysteriously leak out into what a multimeter will tell you is a definitively open circuit. If you're thinking of doing something like this again, I'd suggest: 1. Definitely use PLCs, their inputs are inherently hardened and you can use 24/48/240v signalling voltages - and by extension a whole universe of very robust industrial indicators and switches. 2. Don't use data cable for non-data transmission, the twisted pair coupling will give you issues you don't want and the stuff is fragile as anything. If you want a good cable which supports multiple non-data channels the term 'pilot cable' or 'control cable' will see you right, that's a multi-core cable which usually has 4 thick cores and a bunch of thin pairs, it's traditionally used for carrying 4-20ma signalling loops in factories and oil rigs etc, it's well shielded. 3. Do use RS485 to loop your PLCs together. 4. Don't use weak voltages on stuff that's being handmade and screwed together onsite. You run into all sorts of transient issues, 3.3v will balk at a loose terminal whereas 48v will romp home if there's even a hint of contact.
- geerlingguy 3y ago
  That was what my Dad mentioned too—he's built a lot of signaling systems for tower sites and radio studios and was nervous about me running 3.3v over any length of Ethernet. But he assumed we'd have shielded Cat5e at least... that would've helped somewhat.
  - 15457345234 3y ago
    Either pullup or pulldown resistors would have helped - you see this a lot in PCB design, even short traces that are used for signalling will be pulled low or high via a relatively high resistance. That ensures that you have a sharp transition when the switch or whatever is closed or opened and that a floating voltage can't appear over time on your line and cause false triggers.
ilyt 3y ago
There are modules where you just have ethernet and few IO ports, for example WISE-40X0LAN series. It's pretty much what you've built but industralized. And, as it is for industrial stuff, pretty pricy, 150 EUR a pop. But works with via both HTTP and MQTT
numpad0 3y ago
> weird bit of a drain on the 3.3v You...had current limiting resistors in series for each buttons, right? edit: I think each buttons could be made to register the last pressed UNIX time rather than sending out button event, so the host can collect reports and sort out time sensitive aspects "later" in the loop to account for delays and reordering type of issues
- 15457345234 3y ago
  How much accuracy do you want? Now you have issues syncing all the SBCs to a timeserver and how much drift their internal clocks have. Some of those things have very vague timing. If timing is critical I'd run all the buttons back to a dedicated device but where you'd find a PLC-alike with 200 inputs polled 'simultaneously' (FSVO simultaneously) I don't entirely know. This is the type of project where very particular issues become annoyingly apparent only after you've chosen a hardware platform.
  - geerlingguy 3y ago
    Quite true. And a few of the hard requirements became a bit softer after we got on-site and ran into the issues that couldn't be solved for lack of time.
  - numpad0 3y ago
    I was thinking more along that rate limit might not be high enough with industrial stuffs, they generally don't like e.g. polling at 125Hz.