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Automatic watering system with capacitive probe and Arduino on the cheap (and I mean it)
> There probably isn't much moisture in the cornstarch until it is openedUp to 15% cf https://www.law.cornell.edu/cfr/text/21/137.211
> It's also possible (but not tested) that any unused oogoo left over could be saved in a vacuum bag.My bet: t's not gonna work very well - any moisture in the corn flour is going to trigger polymerisation - this is why you have shorter cure times even when the molded objects are massive.
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> using an SLA for my auto door chicken coop (solar charged) and usually have to replace this every 6 monthsI'm curious: "replace" as in what? As in "discard the old battery, is dead" or as in "solar panels don't manage to keep it full, I put in a fully charged spare and recharge the removed one from the charger"?> It gets pretty hot in Summer(you tell me... come Jan, I long for the miserable 4-seasons-in-a-day Melbourne)Maybe it's a good idea to dig a hole and host the battery in. But then again, keeping it dry in rainy days may be more trouble than it worth.> I haven't found any serious issues with power loss due to heat.The infos I found over time tell that only the life-time is affected - this usually translates in loss of charge capacity, not in power capacity (i.e. the battery will still be able to deliver the same amount of power, but will run out of juice sooner).
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What else to say than... really cool!Thanks for sharing.
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Thank you indeed.Based on the photos, I'll stay clear from smart-prototyping. It's not the damage on the packaging that worries me, it's the defects on the solder mask (photos 5 and especially 6) - potentially, they can make the affected probes unusable outright or kill them in the long run (water getting under the solder mask) - the probes, including connection, must be absolutely waterproof.If you need them all (can not afford to discard the low quality ones), I'd suggest you cover the affected areas with some waterproof coating - finger crossed the coating will stick on the existing solder mask.A drop of UV-curable solder mask would do http://www.ebay.com/sch/i.html?_nkw=uv+curable+so...(make the area clean of any greasy substances, let the solvent evaporate, apply a small drop of resin on the affected area and spread it thin, expose it the UV - in the sun for 30 mins will do http://www.instructables.com/howto/uv+solder+mask/).You'll need to cover the area of wire connections anyway, so alternatively you may apply the same solution for the damaged areas. As explained in the 'ible, I used acrylic nail monomer+powder from ebay (the powder contains not only the pigment but the polymerisation catalyst as well). The aesthetics of the result may not be high (I'm not a nail artist), but the electrical insulation is perfect and the mechanical strength is better than that of a varnish or lacquer.
Sure I will post "I made it" as soon as I get the solution to work. BTW, I got the PCBs on for two days ago. Here you go some pics:1) Package2) Small damage on the plastic envelope. No PCB damaged.5 & 6) Small failure on the silkscreen on two PCBs7) One board is slightly bent
Good luck.May I kindly ask you to post an "I made it" picture when you got them?Do you intend to use them with the circuit in this 'ible? (the price I paid to pcbway for the controller board was $12 for 10 panels with 4 boards each. Without shipping. Dam', the express courier fees are - almost literally - highway robbery).Cheers
> I ordered 5 boards (5x5=25 probes) with a total cost -including shipping, of $16.79.Interesting. At this price, I guess the shipping is by snail-mail rather than expres courier, am I right?> They found that one of the files had the silkscreen with the necessary dividing lines so they are Ok to produce them without extra cost.Ok. If they don't score a snap V groove along that lines, take care how you separate them. Anything (scratch and/or badly insulated connection) that allows minute of water shorting two traces via soil moisture and your probe is useless.(e.g. in my circuit, the NE555 bounces the probe between 1.67 and 3.33 V. Given the resistors, peak current is somewhere around 3.33V/25K=133uA - doesn't take much to drain such a low current).> I offered smart-prototyping.com to either manufacture the boards with a dividing line on the silkscreen based on the already provided Gerber files or to reimburse me the money.In my experience with pcbway, they examine the gerber files and only after that they quote me the final price - so I pay nothing until their price is final. No surprises, no delays on haggling over the price; and if you explain them from the start what you want (e.g. separation V groove, etc), no delays whatsoever. Plus, you can monitor online the progress of the PCB fabbing between different stages.
I offered smart-prototyping.com to either manufacture the boards with a dividing line on the silkscreen based on the already provided Gerber files or to reimburse me the money. They found that one of the files had the silkscreen with the necessary dividing lines so they are Ok to produce them without extra cost. I ordered 5 boards (5x5=25 probes) with a total cost -including shipping, of $16.79.
How many probes do you need?> After checked your Gerber file we found there are 5 separated sub-boards, it means we have to charge you additional 41USD for it.Just from curiosity, how many did you ask them to do for you? (just to understand what those $41 come when considered for one piece).The probes are layouted, indeed, 5 pieces on a panel of 100x100mm, with a snap groove between them. You can ask them not to separate them and only draw a line on the silk layer, but it will be you to cut them along that line; believe me, cutting pcb-es is a thing to be hated - see here http://electronics.stackexchange.com/questions/115...As the probes are already printed and insulated, the only thing I'd recommend is the heavy-duty knife, use a new blade and score it carefully before snapping.> Can you please suggest what to do?My advice? Change the pcb-fabber.If they want you to pay extra, it's their right. As it is your right to reject the deal if it is ridiculous.On pcbway.com, I paid $33 for 10 such panels (a total of 50 probes), with a snap groove already marked.If you need just a few, I might have some spares, PM me and we'll discuss the price.
I ordered the probes from smart-prototyping.com by sending the Gerber files available on this project (8 files under square1-planecap/print/grbl). I got the following comment: <<After checked your Gerber file we found there are 5 separated sub-boards, it means we have to charge you additional 41USD for it. Or you can design a big outline without four lines inside, then you don't need to pay extra money.>> <<Boards which are separated only by silk-screen are not counted as sub-boards and don't have to be payed extra>>.Can you please suggest what to do?
> but it might not be the best idea to publish a circuit that is faulty in so many ways as an instructable.Not a bad idea either, mistakes can be as instructables (or even more) as successes - one has only to admit it. (errare humanum est perseverare diabolicum)In this case, it's easy to fix - the author should just edit the 'ible, put a comment in bold at the top saying the design is faulty and...a. let others trying to figure out why is it so... b. ... work to improve the design (don't bother with the USB connector until you aren't sure its good enough)...c,... update the article once the design is good and tested. Make sure to include the details why the pre design is faulty and how the new design corrects it.
> So can you please help me with the proper design and share an image below.Sorry, I can't - time restrictions.Besides, your 'iblle, so it should be your work, not someone else's (does it feel any good in just following instructions?)> My requirement is, voltage should be between 4.5 to 5 volt and current should be below 25mA and I don't want to use heat sink(optional).Well, I can tell you no amount of passive components is going to met both of the requirements - if trying to limit the current by resistors, you'll take a hit on the voltage.Which means more occasions for you to learn. Like:- current limiting - start from https://en.wikipedia.org/wiki/Current_limiting and use Google for other pages- short circuit protection - after all, what you want should keep into account the "What if the output is shorted? How will my current behave?" While googling for it, visit the "Image" section, you are likely to land on interesting schematics - visit their page (and learn).Also think (or get to know) other situations resembling yours. E.g. using LEDs, mostly the power LED variety, will mean that you'd need to limit your current (Google for "LED thermal runaway" to understand why) - see what others are doing to avoid it (Google "power LED driver voltage regulator" the first link returned is an 'ible showing how to use a linear voltage regulator - rather than a fixed voltage one - to create a constant current source. Maybe by changing some components you'll get better designs... or maybe not, but at least you'll get to understand why).Potentially, other ideas would be: "if I have that regulator that is so limited, can I add something to the circuit to help it do better when needed?" See where googling "voltage regulator higher amperage" will lead you (again, you'll find other 'ibles doing just that)
In your approach, what happens if you connect a 330R as a load (instead of using just a DMM?). Try, measure the voltage across the load resistor and post the answer.If building a voltage regulator is so simple, why do you think others are using more complex circuits? They'll surely be more expensive and (due to a higher number of components) more prone to failure, so...?
> I always like to my make my life bit difficult to have fun.I'd suggest you to change your target into having fun while learning.Helping you with the second part:> The purpose of D1 is to stop the reverse polarityThe move it before the IC - it doesn't help if the IC feels the effect of the reverse polarity (between pin 1 and pin 2) before the "protection" is reached. Incidentally, this will also make the drop in the voltage introduced by D1 come before the regulation - thus the IC will "feel" in it's input 9V-0.4V but still provide those 5V in the output.> i am using a 9 volt battery as my input source and this is also the purpose for using 39ohm (R3).If you want to limit the input current in the IC, what's the purpose of R2 in the output?
http://www.talgaresources.com/irm/PDF/1665/Seeking...See page 2 for applications.
Would you mind to link that article? Or provide a DOI number at least?
https://arxiv.org/pdf/1310.7371.pdfElectrochemical method with alkaline electrolyte seems to work better.Works at 10V, uses KOH at pH13, the graphene sheets are less wrinkled, needs alternating the polarity though (every 5 seconds) to obtain 2-4 layers sheets of graphene (i.e. you'll need to use some electronics to do it for hours)
> With the 2-volt acid method, I get millions of exfoliated 1/4 inch flakes.By the look on the photos you have, your flakes are still graphite rather than graphene - i.e still in the micron rather than nanometre thin. Maybe it's a fine graphite, but still graphite only. The $20000/tonne the scientists are after is graphene - sheets up to 10 layers of carbon, a single layer preferred.> Still looking for an application for them.Continue watching RobertMurraySmith until you get to supercapacitors. Or conductive ink.
As you already have 1 probe approx 20x100mm, with 2 single-sided back-to-back, I think that 2 single-sided back-to-back 45x45mm (too keep the same surface, same PCB thickness, but minimize the fringe).As a third data point, and only if you manage to find scrap, a 2 single sided 10x200mm would be interesting, especially in low moisture content.
> As I didnt have double sided PCB, I used 2 pieces of single sided glued together.That may explain why the electric field lines may "jump to the chance" of closing through moist soil rather than the PBC (once the soil is moist enough) - the most usual PCB is 1.6mm thick, double that for two pieces back to back glued together:3.2 mm, maybe 3.4 adding the dried glue thickness.Given that the PCB substrate has a Kr (eps-rel) of around 4-5 and water around 80, with a narrow-but-thickish probe one may "convince" the entire area of the electrodes to "send" field-lines through outside of the probe rather than through the PCB substrate (see Principle of least action)Would be interesting to see the probe capacitance in water varies between a narrow probe (say 10x200 mm) and one with the same area but squarish (say 45x45mm) - if my hypothesis is right, the narrow one should reach a higher capacitance; in the case of the square one, the areas close to the centre would prefer to close their line fields through PCB (their "field line trajectory" becomes too long if going through outside, even if the outside is more ...umm... "electrically permittive" than the inside).
1. to me, came as a surprise that, in wet soil, both probes have almost the same capacitance. When I'll have time, I think I'll set my hands on an electrostatic modeller to see exactly how the field line go2. when I experimented with probe pattern designs, I needed to factor the scarcity of water - I simply could not afford to over-water the trees for 1 month only to fail them afterwards.How's that relevant? If you don't have water restrictions*, going with the cheapest design seems sensible. If a simple piece of double-sided PCB is good enough then it effective and, surface to surface comparison, less expensive than the PCB you'd be using.(*do consider all factors related to water restrictions. Throwing half a litre more/plant on a veggie patch won't cause the same troubles as a potted plant set above your high quality carpet; your significant half may object the most strenuously to the amount of water you use, be it automated or not).
Comparison of capacitive soil probes
You can even "paint" yourself the electrodes on a plastic (a PVC pipe is much cheaper than stainless steel and easier to handle). I've done it with a suspension of graphite powder in a solution of polystyrene in xylene - the result is a conductive layer. (just search "conductive ink" on youtube and watch the clips having Robert Murray-Smith as the author) The downsides: - it's hard to control the resistance of the "painted" electrodes themselves - thus from the start each "probe" will need it's own calibration. Not a big issue given that this would need to be done anyway due to the soil variability - I can say nothing about the stability of the electrodes/resistance over time - I'm not worried about corrosion, but I'd keep an eye on mechanical stuff (abrasion mostly, cracks due to bending)
Here's an idea for those of us that have burned pro minis by installing them backwards:Instead of putting all pins on the pro mini, and sockets on the PCB, put 1 set of pins on the pro mini, and the other set of pins on the PCB. so each side will have a row of pins and a row of sockets. Almost murphy proof, except for setup time. If you are careful enough, not really an issue.Yes, I have several pro minis in my junk box from this reversed installation issue.......
I was not thinking of using a much higher resistance for charging the probe capacitor. I assumed you did not need to measure the absolute value too accurately just the change in value on dry/wet days, you say the probe capacity is ~80-200pF presumably in air, but not how much it increases to in wet soil. Anyway with the same 50Kohm used on the NE555 I a guessing you would get a charge time of about 2uSecs dry going up to as much as 10uSecs when wet - and a 16MHz AVR should be able to discriminate that enough.BUT, prompted by this project I have found this REALLY neat way of accurately measuring very small capacitors :-http://wordpress.codewrite.co.uk/pic/2014/01/21/cap-meter-with-arduino-uno/(don't be put off by the topmost title referring to PICs)The comments suggest an improvement by not relying on stray capacitance by adding a 100pF, and maybe limiting charging current with say a 470Ohm resistor..But in any case it will measure accurately without relying on time constants, or having to measure frequency, and all without a NE555!You may also not be aware that AVR power consumption depends on supply voltage and frequency. If you burn its oscillator configuration fuses to use the internal 128KHz oscillator, and run it on 3Volt it will only use 0.1mA even without sleeping. The internal oscillator is not too accurate, but if not measuring frequency that would not matter.So now I am thinking change to a 3 Volt pump, no regulator for a bare AVR IC, and run all off a suitable 3Volt battery. You may have to beef up the transistor used to turn on the pump.I found this pumphttp://www.ebay.com/itm/2PCS-Ultra-quiet-Mini-DC-3-6V-120L-H-Brushless-Motor-Submersible-Water-Pump-New-/201558912416Hope these suggestions are of use.
The 1N4001 or 1N4004 are cheaper than 1N4148 and rated at 1 Amp continuous.Most Arduino pins have an input leakage of 1 Microamp so not so high impedance, but the analog comparator input has only 50 Nanoamps leakage! - so is ideal for monitoring the voltage rise on the probe capacitor, doing away with the NE555.In this case you would turn on/off an Arduino pin feeding the charging resistor, to charge / discharge the probe capacitor, and measure the time to reach a threshold value as seen by the analog comparator compared to a reference voltage, which can be the internal precission bandgap reference.Google some Arduino circuits for measuring capacitance for more info.If you stick to the NE555, you do not need a 10uF electrolytic on the CV pin 5, it is meant to decouple high frequency noise, which an electrolytic will not do, a 0.01uF non electrolytic will suffice. However the Bipolar NE555 produces large current spikes on the power rail every time it switches. Therefore you might consider using the CMOS ICM7555 equivalent at much the same cost - but DO use it in the more conventional astable configuration - not using the output pin 3 to also charge the timing/probe capacitor. See for example page 5 of the Intersil ICM7555 datasheet. Also it often does not need a CV capacitor at all.Have you thought about using a rechargeable battery with solar cell charging ?Maybe too expensive but might save in the long term.
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