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If you're like me and have trouble keeping your calatheas and pepperomias happy and not overwatering them to root rot ruin, why not take a gander at…
Read moreHey @MarkMakies,
Thanks for bench-testing this! This will be great info going forward.
It’s very odd that it responds well to wet tissue, but not to a plant pot. Can you send an image of your physical setup testing the device in a pot?
Hi Mark
Just butting in a bit here
Would the sensor be a bit close to the edge of the pot by any chance. I am not sure if it should make the difference you are seeing but you never know just what the moisture distribution out to the edge of the pot is like.
Cheers Bob
Hey all,
Good idea regarding the moisture distribution @Robert93820! The device from DFR is actually to position it as close as possible to the edge of the pot, with the “front” of the device facing outward.
I did notice @MarkMakies, the WLED on the face of the device looks to be off in both images, contrary to the DFR test images which see it either red or green. See below. Is this normal? I wasn’t aware of an “off” state for the LED in this case.
Re: the power changes in the third test, I’ll look into power consumption. I would have thought the bank was perfectly fine, but its possible it may have caused an issue.
How hot is the greenhouse exactly? I would think that could be the cause of the issue, depending on the actual temperature.
Hey Mark,
Thanks for clearing up the LED.
I must’ve swapped the power bank test around when reading, all good.
I can’t imagine those temperatures could be causing issues, particularly for a device designed to work in hot/humid/wet environments.
Typically I would consider testing this at our warehouse, but I don’t believe we have any planters anywhere.
Hi Zach
If Max current is 15mA it could well be the issue. These devices are meant to charge another device in the absence of a mains charger.I believe “end of charge” is detected by a reduced output current requirement.
At 15mA max it is quite probable the power bank was switching on and off. I don’t know how many times this would happen before switching off completely.
This subject has come up many times and usually results in problems caused by using a device for a job it was never designed to do.
Cheers Bob
Just noticed this. Surprising, as in the past it has usually proved to be THE issue.
Another EDIT.
Is this a 5V power “supply” or a phone charger of some flavour ie Samsung etc. If a phone charger it is possible it would like to “see” a phone at the end of the cable to function properly.
The possibilities are pretty endless and without knowing EXACTLY what all these devices are I think most answers are a bit of guesswork.
Hey @MarkMakies,
Interesting… I have two questions:
You mentioned the scope is measuring power to the plant monitor, is this power instability mirrored on the 5V power to the dev board?
Does the timing of the dip correlate with something? Does it happen randomly, or periodically?
Mark.
Are you measuring with 10:1 probe on the scope or 1:1. If 1:1 the bandwidth might be reduced. I think you have a larger pulse than what is showing as you are triggering reliably. If you look carefully you will see the trigger point is lower than the scope trace gets. I am assuming negative going slope for the trigger.
If you extend a line down from the top trigger indicator where it crosses the trace is the trigger point. As you can see this occurs where the 2 traces are the same amplitude (approx). This corresponds to approx 3.15V. Yet the trigger level is set to 2.9V (right hand indicator).
You seem to be triggered reliably so this suggests the signal is actually about 2.9V at the trigger point with the further likelihood the actual pulse is reducing to quite a bit below 2.9V.
What flavour scope is that. Are there any more values on screen which might be of assistance.
As I have said several times in the past getting full appreciation of what you are looking at is having some knowledge of the relevant limitations of the instrument in use. All instruments are useful if you know these limitations.
I am not saying I am absolutely correct here but I don’t think I am far out.
You could re scale that trace by picking the trigger point then using this as 2.9V rescale the trace to suit. Use percentages don’t just move the trace down. You will probably find the lower level to get to about your 2.4V or even a bit lower. Would be an interesting exercise.
Cheers Bob
PS. If you get to the bottom of this you will possibly find you have fixed quite a few future problems that have not even happened yet.
Hi Mark.
Well this is a good one. For what it is worth 20mSec is 50Hz, Mains frequency. Might be significant might not, just keep it in mind.
At this stage I would transfer my attention to all the other bits. For instance are you using Arduino or RPi.
Monitor that 5V rail and start disconnecting things. There is something going awfully astray here. Have you available a 5V supply with some grunt like about 5A or so. Even more if you have it. I can’t get rid of the feeling there is nothing wrong with your sensor and there is something in your system pulling the power source down in a fashion which is near cyclic but just not cyclic enough to point the finger at any one source.
That yellow trace looks like something turned on to do something for about 100mSec. Do you have any WiFi or RF device powering up for this time?
Cheers Bob
Hi Mark
What do you mean by that? Scope traces good or still bad.
No. More likely the earth clip. You need to go over all your ground connections thoroughly. You are either fixing a problem with the earth clip or creating another one which cancels out the original.
Try with only the earth clip connected. If all OK under these conditions you should be able to remove the earth clip while the system is running and observe results.
I assume your scope connects to earth via the mains plug and it is not a battery tablet type.
As a point of interest I might be considered a bit naughty but I run my scope with the mains earth disconnected. I do this with a short bit of mains (300mm) extension cable with the earth wire hanging out to be obvious. If I want to reconnect the earth I just remove this short bit of cable.
I have found over the years particularly with Television you can often introduce problems that are not really there just by using the mains earth. In your case just the opposite seems to be the go. You fixed your problem.
Cheers Bob
Hi Mark.
OK so you have just done what I suggested. Good.
Now we will “clutch at a couple of straws”. Where do you live. Are you on the power grid or a rural set up where you generate your own power. If the latter you could have any sort of strange set up.
I have actually dealt with a set up where they sometimes used our australian style of power socket. They generated their own power but had to accommodate both 120VAC and 240VAC equipment. Easy, they just centre tapped the 240VAC supply and connected that to earth. If you need 240VAC you connect between active and neutral. If you need 120VAC you connect between active (or neutral) to ground. Worked but caused some headaches.
Similar situation on board some ships with the added problem of 400Hz mains.
Cheers Bob
Hi Mark
Methinks you have a bit of sleuthing to do.
You may have just found a bit of a problem you knew nothing about.
If I may make a suggestion. Don’t put a “band aid” on this by just connecting an earth wire to where the scope lead has been connected. Of course this might be the problem but it could also be a problem somewhere else that you will just cover up. You might do well to have your whole premises checked.
I can’t think there is a lot more that can be done remotely without actually sighting what you have unfortunately.
Cheers Bob
Hi Mark
One thing we have not seen.
Can you post a circuit of EXACTLY what you have and EXACTLY how it is all connected please. Just on the off chance that a fresh (as fresh as 88 YO can get anyway) pair of eyes might spot something not right.
Running out of ideas
Cheers Bob
Hi Mark
This is a worry. When you used your bench supply that is what I meant by another 5V supply with a bit of grunt.
it is “dew” (as in dew on the ground) not “due” but that is trivial. You are probably correct. When this happens you will get a rapid rise in moisture even if it is on the ground surface it probably would be detected by your sensor.
Now to the other bits.
I assume the sketches are EXACTLY as drawn with absolutely nothing else connected.
I think you have proven your set up is OK. as by connecting battery or isolated lab supply everything looks normal.
Your problems seem to happen when you power from anything plugged into the mains socket, this includes your PC. This still points to something funny back on the mains side of things. This is going to some sort of extreme but being rural I don’t suppose you would have a battery and sine wave inverter would you. If so you could try running your set up with that to attempt to pin point your problem. This probably needs to be a SINE WAVE inverter as the approximation type inverters are just that, very approximate.
Also another check. Can you try another GPO. I assume your GPO tester checks for things like reversed active and neutral. If you are using a double adaptor take this out of the equation. Don’t know about these days but some of these things reversed A and N on one side. Clutching at straws here but I am running out of ideas
Cheers Bob
I have one more idea
Councils have a system where off peak hot water, street lights etc are controlled by a “ripple” signal on the power lines. At my place it is large enough to cause my LED bedside lights to flicker quite annoyingly. Usually on the half hour after 10.30PM is most noticeable. Off peak water systems have a “ripple receiver” on premises. It does not matter if you have something like this or not, the signals are there.
I would have thought though the power supplies would have absorbed this but you never know. My lamp doesn’t.
You could try something. Do you have a 12V power source that plugs into the GPO, NOT your lab supply or battery. Feed this through a linear voltage regulator like a 7805 and power everything from this. The 7805 will supply about 1A continuous and will remove any signal ripple on the 12V mains supply. The sine wave inverter will do similar as there will be no signalling on that.
You have had a linear 3.3V regulator on the moisture sensor but any ripple could be upsetting your controller. If you can input 3.3V to your controller putting your linear regulator before everything might fix it.
Hi Mark
Understood. Beat of luck there I saw that on TV and Computer news yesterday and when I got your post Re fires I thought that might be where you are.
Had a couple more possibilities above . Post crossed over.
Cheers and hope you are all OK.
Bob
Hi Mark
I would have expected a hell of a lot less than 10MΩ. 62mV in 240V is not much. I have not got too many ideas on how significant that is. The electricity authority will have a procedure for measuring these earths but I do not know any details. If you have a contact or an electrician mate they will have more of an idea. A nice new earth stake would not do any harm.
Two different earth systems can differ quite a bit. I was once at a TV transmitter installation where there existed a “mains” earth and a “technical” earth which was far superior. The difference, about 80VAC. The roofers picked that up. The roof sheeting was connected to technical earth and the electric drill being used was connected to mains earth. Every time the drill was withdrawn from the roof, BITE, enough to get quite a surprise and possibly fall off the roof.
Cheers Bob
Hi Mark
Well, that is pretty comprehensive.
We will start with the inverter. “Modified” sine wave was the word I was looking for when I said approximation. Modified is right as it usually looks like a cross between a square wave and a sine wave with about 100% 2nd harmonic distortion. Not usually recommended for sensitive circuits. but we tried.
Your conclusions:
1, 2: Probably.
3, 4: I still think there is something about your mains that the plug packs don’t like. The difference between them and your lab supply is plug packs are switch mode and lab supply is linear (analog). The analog supply seems to handle any crap far better which I suppose is why these things are still linear supplies, a lot cleaner. Still a case for analog in this digital world I think.
7: You seem to have proven that.
8: 7805 is OK for 12V or 9V plus pack. This IC has a drop out voltage of 2V or a little more. This means that at about 7V input it will start to lose control.
9: If using a nominal 7.2V (2S 18650?) the 7805 will be a bit marginal. Change to a “low drop out” regulator such as a LM2940CT-5.0. This is a fixed 5V regulator good for 1A and a drop out voltage of 500mV which you can get down to about 6V input with full control. Available Jaycar cat no ZV1560.
The linear regulator is very good at removing ripple and any crap that stays above the drop out level. If such interference is so bad or the regulator is operated close to drop out it will allow lower voltage excursions to pass through. I don’t think anything would stop something this bad but your battery has an extremely good chance of staying clean.
I would still do some investigation of your mains supply. Load up those plug packs to about 0.5A and see if you can get some bad scope screen shots. Or even feed the mains into a low voltage transformer terminated with a resistor and this should display something like what the mains look like. Time of day will play a part here if the problem is off peak ripple signals. If you can find the right ear to bend you might have a case for an investigation by the electricity authority. Check with your friendly electrician. Others may well have problems also.
Cheers Bob
It varies. I have some that do an excellent job - great stability right up to their rated maximum current and no sign of ripple. I have others that are quite hopeless. One of the awful ones turned out to be from a device that contained only a small heater - it was never intended for electronic devices, and performed accordingly. A lot of the low-current adapters are just capacitive droppers with little or no additional filtering - they are usable at very low loads but perform badly at anything approaching their rated current.
Hi Jeff
Well said, would have to agree with that.
But Mark has too many switch mode devices connected to the mains giving trouble. I don’t believe they ALL would be crook. There are some well branded (Belkin etc) ones and even his PC USB supply that caused problems. The only switch mode device he used with success was the power bank but significantly that was not connected to mains.
So to me it all points to something the switch mode systems don’t like that is ADDED to the mains voltage. He could look at the mains directly but DEFINITELY NOT RECOMMENDED AND VERY VERY DANGEROUS. That is why I suggested looking at the secondary of a low voltage transformer to possibly see something amiss.
Mark has said he is rural so there could be anything connected causing problems like speed controlled rotating machinery or some other large current use devices. I think you would have to be there and have a look personally to form any definite opinion.
Mark also says he is about 40M from a transformer which I assume is stepping down from 11kV distribution. Is the transformer faulty in some way? Is it a wooden pole, these are notorious for causing interference when they get older. Go out and have a look at night. Might frighten you sometimes with the arcing running up and down the timber. Especially if you hit it with a rubber hammer.
Cheers Bob
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