I’ve got a question that I’ve tried to answer by googling but I’ve never been able to find anything that helps.
I have a septic tank alarm system that turns on an audible and visual alarm when the float switch detects that the tank is 3/4 full. There is a pair of NO dry contacts that close when the alarm goes off.
How do I monitor whether the contacts are closed or open? I assume with a GPIO pin, but I’ve never been able to google this question and find anything of use.
I’m ready to give up and use a RIB01BDC [0] packaged relay to turn on a raspberry pi and email me when the septic tank contacts close.
> How do I monitor whether the contacts are closed or open? I assume with a GPIO pin, but I’ve never been able to google this question and find anything of use.
Without making assumptions about the microcontroller used, attach ground to one of the contacts, then attach a GPIO pin, the other contact, a 10k resistor (or 100k), and VCC together in series. The microcontroller should periodically read the GPIO pin. If it reads high, the contact is open and the alarm is not sounding; if it reads low then the contact is closed and the alarm is sounding.
The GPIO / contact / resistor / VCC arrangement acts to pull up that side of the circuit to the high logic level, and the resistor will limit the current that flows whenever the contacts close. If your microcontroller has an internal pull-up configuration for GPIO pins, you may be able to attach the pin directly to the contact without the extra hardware. (Conversely, if it has a pull-down configuration you can reverse things, attach VCC to the contact and the GPIO directly to the other. Read your microcontroller's documentation for available features and any current limitations.)
The very first thing to do is read the manual for the installation and/or parts used. Second, approach the tank setup with a high voltage multimeter and carefully and safely take measurements of what you might be dealing with.
> The very first thing to do is read the manual for the installation and/or parts used. Second, approach the tank setup with a high voltage multimeter and carefully and safely take measurements of what you might be dealing with.
Good call, I’ll make sure it’s not 120v or 24v with a multimeter before attaching anything that expects dry contacts.
Thank you for the detailed instructions, this is extremely helpful! I’ll throw a multimeter across the contacts on the septic tank alarm to make sure they aren’t putting out 24v.
I use an ultrasonic sensor and ESPHome to monitor the water level in my sump pit. Depending on what you want out of your septic tank monitoring, this may be a useful option.
> Modules for solar farms have been getting larger and heavier, but the maximum size/weight has traditionally been limited by what human workers can heft into place.
Are there installers that actually use humans to lift solar panels onto racking on solar field projects? I figured everyone was using vacuum pump panel lifters instead of humans these days as it’s much faster and less prone to injury.
I'm trying to find recent Time Lapse videos - here is one from Australia, 2020 - at the time the largest in Western Australia - so at scale. All the panels were hand lifted by one person. https://www.youtube.com/watch?v=uCtFG-hIHdM
- 200 MW
- 1200 Acres
- Piles -- 68,350
- Support Piles (Crew does 80-100 piles/day)
- Tracker System
- 490,150 Solar Modules
- 540 watts/module
- Crew can install 500 panels a day
- These are multi person 2-4 people lifting.
- 500 workers on site - doing 6200 panels/day.
- (That suggests ~40 person crews if all worker installing
panels. Wow - now I see why this is a big deal)
- Cables panels -> Inverters
- Big Inverter install to to convert to AC
- Lots of concrete pouring for substation/Inverter Pad.
> Do you really think this is what happens on job sites? Does this match your personal experience?
Yes, it does. I’m a construction project manager, I’m not having my crew do any work that isn’t represented in the current revision of the plans and specs without approval because that’s the only way you get paid for the extras. Also if it’s an unapproved and unwanted change, you have to pay to remove it. Anyone managing a project who cares about managing their risk is going to submit RFIs and RFCs for every change.
It’s possible that the (tiny and insignificant) residential market is different, but that’s how commercial and industrial construction works.
It’s possible some tiny and insignificant changes like moving a receptacle or data opening a couple inches aren’t properly documented on the as-builts, but major changes almost always are.
> Because my initial reaction was to laugh to myself at how rarely contractors, subcontractors, and crewmembers would actually engage a process like the one you are describing here.
The firms you hire to work on your house aren’t representative of the firms who manage or work on commercial and industrial projects.
> It’s possible some tiny and insignificant changes like moving a receptacle or data opening a couple inches aren’t properly documented on the as-builts, but major changes almost always are.
Based on these responses I should have been more clear. These small and inconsequential things are what I'm referring to. Yes, the projects I'm familiar with track the medium and big stuff, and most of the small stuff.
I have seen multiple thousands of dollars of precast concrete get junked because an edge was less than half an inch out of tolerance. Multiple times. I have myself rejected multiple thousands of dollars of rebar because the hook length was short by less than an inch. Nothing that is shown in the plans or specs is inconsequential and payment doesn’t occur absent an approved variance.
> I hope it's okay to ask this question. For you that have these sensors, what actions do you take based on what they tell you? Open more windows when you're cooking? Put on a mask when you vacuum?
I don’t get it either, there’s not much you can do with a residential AQI sensor without adding a bunch of other automation controls.
Commercially, these are used in building automation to do things like turn on the exhaust fans and make up air units in a parking structure when the CO levels go up, or to open an outside air damper in an AHU to let more fresh air in if elevated CO2 levels are detected.
I just don’t see the application for residential use. It’s just a PPM number, does anyone actually take action if the number gets too high? Anyone automate their actions?
> there’s not much you can do with a residential AQI sensor without adding a bunch of other automation controls.
You don't need automation. I have a portable CO2 monitor (aranet4) and it gives me an indication of how effectively the air is being exchanged. I've learned that my desk location at home is ok during summer and winter, but when temperatures are moderate the furnace isn't running as much, and the CO2 will get quite high. I keep a window cracked when I work there and it's enough to bring it down to reasonable levels. I didnt know this information before getting it. Similar when I was visiting relatives over easter - the CO2 in the bedroom got up to 2500ppm wile I slept (old house, sealed tight but no forced air circulation). I opened the window for the rest of my stay.
I had a similar experience. I got a cheap CO2 sensor from AliExpress, I basically would open a window or the door to my office if it got over 1000 during the day. I don't consciously notice a difference, but it also measures pm2.5 levels and I was surprised at how high they get while cooking.
Then for shits and giggles I brought it with me to the inlaws and after turning it on there was shocked the CO2 levels were 4300ppm!
Suddenly the headaches they would get at home made sense, and they've started opening windows in the mornings to help circulate some air.
Super fast reply from someone else - Yes, I have a standing air filter unit. If PPM went up I’d kick it into max gear.
(Now I have it running on very low continuously and it keeps PPM down)
The unit is rated for spaces 2x my square footage so on max it makes a quick improvement.
For CO2, minimize cooking / burning and kick on the air to attempt circulation. Worst case leave for a bit. (Used to be very sensitive to CO2 levels, it’s getting better).
> The concern is with non-profit hospitals. They don't distribute profits to shareholders. But some do pay high salaries to employees or have large and growing endowment funds.
The non-profit healthcare organizations in my metro area spend tons of money expanding by building new clinics, surgery centers, specialty clinics, hospital wings, etc.
Instead of paying out profits to shareholders, a non-profit hospital/clinic will use their excess dollars to build new facilities, buy new equipment, and add the capacity to care for more people.
How is that worse than a for-profit company? If your local healthcare systems are not expanding while the regional population is expanding, you’ll have less care available for all regional residents.
There are ways to abuse non-profit status, but operating a large hospital and clinic system isn’t one of them.
You can hold on to your stock and avoid paying capital gains taxes and still diversify your portfolio by entering into an equity swap contract where you receive a rate of return equivalent to an index benchmark (or any asset, really) while the swap writer would receive the returns of your single stock position. Both parties would still hold their original assets (or futures/options contracts), but would receive the returns from the asset of the other party by marking to market and making net cash payments to each other on a regular basis.
You still hold the original asset, but receive the returns of an index instead, so you’ve diversified without incurring any capital gains tax.
The swap writer would likely hedge their risk (shorting stock or using options) and make money by charging fees/premiums for writing the swap.
I have a septic tank alarm system that turns on an audible and visual alarm when the float switch detects that the tank is 3/4 full. There is a pair of NO dry contacts that close when the alarm goes off.
How do I monitor whether the contacts are closed or open? I assume with a GPIO pin, but I’ve never been able to google this question and find anything of use.
I’m ready to give up and use a RIB01BDC [0] packaged relay to turn on a raspberry pi and email me when the septic tank contacts close.
[0] https://www.functionaldevices.com/product/rib01bdc/
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