Remote pump control ideas.

[stj]

Re: Remote pump control ideas.

78s05 can supply 1.5-2A

so how much current at 5v do you actually need?

[Dannyx]

Re: Remote pump control ideas.

use a 12v psu - easy to get.
then add a 5v regulator for the electronics.
ideally a linear one using a 7805 for long term reliability.
not that i dont trust buck convertors - but they do have more to fail.

7805 is too low for the GPON though - only the STM board may run at that. I'm currently running both boards (pump and tank) on 12v using their onboard regs. I also made a mistake regarding the power draw of the GPON - it's 0.5A, not 0.2A, so a bit more than I originally had planned.

btw, how much watch flow is there?
because a small water powered turbine generator would be a sneaky solution.

None actually - it's a tank dug underground, so I only ever see the calm water through a hatch at the top. I have no idea how it's transported there or where the pipework even is, plus such a project would take too long to pull off and requires too many parts.

[stj]

Re: Remote pump control ideas.

use a 12v psu - easy to get.
then add a 5v regulator for the electronics.
ideally a linear one using a 7805 for long term reliability.
not that i dont trust buck convertors - but they do have more to fail.

btw, how much watch flow is there?
because a small water powered turbine generator would be a sneaky solution.

[Dannyx]

Re: Remote pump control ideas.

Well, just in case someone is curious about the status of this project and how it turned out in the end, last week I managed to install the end product at the actual site and I'm happy to say it works as I planned it, but there are still a few quirks I'm working on...

At the moment, the chaps over there informed me the setup works, but the board located at the tank up on the hill keeps going offline. This is the end which is solar-powered.....not a lot of sun in the past weeks over there, only rain and clouds, so I was seeing it coming to a degree and warned them about it. To solve this, they're going to have utility power ran to that shack, but in a pretty unorthodox way, which itself gives me another problem to solve instead of relieving me of it: instead of connecting to the grid like a regular consumer, they're going to cut some corners and expenses by grabbing electricity from the street lights system instead....even though these guys ARE the officials and such a decision doesn't make much sense to the common layman who's not into how politics and official stuff works Of course, this means that power to my shack will continue to go out and come back on, but at known intervals, along with the lamp posts in the village which also turn on and off at dusk and dawn respectively. So I still need that battery in there, but at least now I can charge it.....how ?

This is where I'd need some pointers, since I'm not sure how I should deal with this situation and what power supply to get for the job.

Our first candidate is the same I installed down at the pump shack: a Meanwell ADD-55A - a 12v+5v supply with battery backup. I was going to go with this one up here as well, but then I realised it would not be able to charge that 20Ah battery enough to last over the course of a day when the street lights go out. The charge current is only 0.23A. It may be enough for small outages, but I doubt it'd last more than a few hours...

This lead me to our second candidate, which is this Meanwell SCP-75-12: a 12v only supply, which also has battery support. The reason I put these two head to head in terms of how they handle battery backup is because the first one appears to have (as the datasheet claims) a dedicated battery charger circuit, while the second one puts the battery straight on the main output, with just a diode in between. This would allow me to push more current into the battery by simply increasing the output voltage. This leads to problems with the STM32 and GPON which may not like the 14-15v the battery requires to charge, so I'd need a step-down converter in there to limit to 12v for my devices. When on battery, this may not run correctly because the voltage drops too low.....

I must admit I haven't measured the current draw of the STM32 board, but I know for sure that ZTE GPON draws 0.2A, that's what the label says anyway. Even if this setup were to draw a whole amp, let's say, which I doubt is the case, it should in theory last a good day with a 20Ah battery. Charging the battery is another story, which is why I'm concerned about the choice of PSU. I only have one shot to get it right, so instead of jumping in, I thought I'd ask for help

[Dannyx]

Re: Remote pump control ideas.

I left the project running in the shop to see how it goes overnight...*insert jokes about fire and other disasters here*

Putting this particular project aside for now, what are some (more or less) ready-made systems that one can use to get into industrial automation, particularly noobs like yours truly here ? I mean, what I did here was build my own system, my own way, the way I saw it in my little brain It's certainly not suitable for anything else and is far from being a "solution". When I think of a more ready-made solution I think of the many "home automation" platforms for the RaspberryPi. These might also work in a pinch and are a huge step up from writing your own "bare-metal" code like I did (plus it has a ton of other features, like a GUI which my system lacks entirely and I AM aware of it) but even those can't really be taken seriously in an industrial setting, can they ?

Proper industrial automation probably involves special hardware and software which costs thousands, so let's exclude those entirely and focus on the more affordable solutions which a small company wishing to enter this field could invest in...

I suppose the general consensus is that it depends on the application....

[Dannyx]

Re: Remote pump control ideas.

dont overthink it - a common ground will exist

Correct, but you know me....I like over-engineering stuff......which is why my projects take so long and I'm not a good designer

[stj]

Re: Remote pump control ideas.

dont overthink it - a common ground will exist

[Dannyx]

Re: Remote pump control ideas.

Yes, outputs can still experience spikes feeding into them, can't they ? That's why I was asking about physically separating the power box from the control box.

[stj]

Re: Remote pump control ideas.

i'm suggesting the 2803 for outputs

[Dannyx]

Re: Remote pump control ideas.

Interesting. Dumb question, but does it provide any isolation so the MCU doesn't get zapped in any way ? The optocoupler is straightforward: there's physically no way electricity can jump the gap between the phototransistor and the LED (unless it's ridiculously high and it arcs)...bare with me, I'm learning here

[stj]

Re: Remote pump control ideas.

instead of the optocoupler you could use a darlington driver like a ULN2803
https://www.ti.com/product/ULN2803A

these have been used in gambling machines for a couple of decades to link the computer i/o to things like stepper motors and relays.

[Dannyx]

Re: Remote pump control ideas.

Back to protecting my sh!t: can I also use optocouplers the other way around to protect "output" pins too, like so ? I saw this setup somewhere on the web, I tested it for around half and hour and it seems to work reliably enough, at least on the bench under normal temperature conditions. It's for powering the 12v relay which in turn provides 230v to the main contactor, since that's its rating...I originally had the MCU pin straight on the base of that 2n2222 but I thought the MCU may not like the arcing that goes on in the 12v relay close to the wire which leads back to the 2n2222. Don't worry about not having a flyback diode across the relay in the schematic - I have a 1n4007 there in reality.

[Dannyx]

Re: Remote pump control ideas.

I don't think the regulator can provide the necessary current to do that, plus I risk damaging it more...tempting, but I don't think I'd do it after all

[stj]

Re: Remote pump control ideas.

hardwire it to 3v3 at the regulator (for max current) and see if you can blow out the shorted gate.
nothing to lose trying!

[Dannyx]

Re: Remote pump control ideas.

well if you are sure it's the chip holding it's own reset line down.

btw, a bit of a bodge, but try adding a pullup resistor to 3v3

I thought of that too, but given the resistance to GND on the RST pin is around 192ohms on the "dead" board and around 7Meg-ohms on the good one, I think something went pop inside the chip.

I removed two 0-ohm resistors which connect together the RST lines of the ethernet chip and the STLink to try and narrow down where the low resistance is and unfortunately it seems to be facing the MCU. There's no solder bridge I can further remove to isolate the RST pin of the MCU entirely, so I doubt there's anything left on that line that can cause this...the only way to find out would be to pop off the chip and see if the reset pin restores to 3.3v...

[stj]

Re: Remote pump control ideas.

well if you are sure it's the chip holding it's own reset line down.

btw, a bit of a bodge, but try adding a pullup resistor to 3v3

[Dannyx]

Re: Remote pump control ideas.

there is no programming for the main chip, only the stlink mcu has code on it.
(and i have that! )

So I can just drop a new chip in, provided the STlink is good ? The board's still detected and even goes as far as to upload sketches to it, but doesn't run anything after that, the NRST pin being asserted low all the time...

[stj]

Re: Remote pump control ideas.

there is no programming for the main chip, only the stlink mcu has code on it.
(and i have that! )

[Dannyx]

Re: Remote pump control ideas.

Turning back to the "dead" Nucleo: I'm tempted to get a chip off Ali to fix it....I doubt it's a drop-in replacement though since it's essentially a computer and requires some programming to work the way it did out of the box. Trouble is I have no idea how to do that, what I need or IF it can be done AT ALL with no external tools and pieces of software...the more astute in this field could probably provide an answer....

[Dannyx]

Re: Remote pump control ideas.

Great pointers as usual. Cheers !

You want the opto to turn on around 1/2 input voltage for noise immunity, not at say 2V but 6V up. The 470R resistor across the opto LED wastes a few mA, so the 1k5 current is not entirely going through the LED. It just ends up increasing the activation voltage to work better with 12V signals.

I see now. What is the math behind this ?

That circuit - the LED lamp sees ~7V when the switch is open, and 12V when closed, so the old/bright dim thing.

Yes - I axed that idea anyway.

Why do you want to run the opto from 5V, you're using three rails already 12V, 5V, 3.3V it's too complicated. I would just make the opto input for 12V.

Yes, it was getting too complicated indeed, so up on the hill, which is battery powered, and there are no lamps to drive at the same time as a MCU pin, I'll be using the 3.3v output for the tank toggle switch. I bench-tested the setup shown in the schematic and it works: I used a single 100ohm resistor in series with the anode of the optocoupler. It might be too sensitive though, as you described, so it could false-trigger (though I do have a pretty long countdown delay time in code before the MCU actually acts and does anything with that input). I talk about battery power and energy conservation here, though probably even 12v across 1.5k resistors in series with the opto's anode would not draw THAT much extra power compared to my 3.3v idea, so it may not be that much more efficient...

For the pump panel which is utility-powered and there are 12v lamps to power as well, I HAVE to use 12v with the 1.5k resistors in series, otherwise I'd run into that issue of not being able to properly turn off the lamps, so I'll do it like in your first schematic.