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  • Capacitor Tester / Capacitance Meter

    I reckon you will discover that the "long settling" phenomenon has little to do with the polarity (why should it?) and more to do with the adsorption/reorientation reorientation of water molecules in the micro-dips of the coating and/or degassing of the same surface. That may be a problem on a scenario in which you empty/replenish your shower tank frequently (who doesn't). However, see first what's the percentage of change between no-settled/settled - if the error is acceptable (e.g. 5-10%) you may not need special solutions to tackle the problem; just make sure you have another small probe just below overflow level to stop the pump and accept a situation in which you know the water level to a +/-5% accuracy using your assumed-linear-but-with-hysteresis bar-crafted probe.

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  • Capacitor Tester / Capacitance Meter

    Plastics have a dielectric constant above 2. One inch of 3/4 plate will get you an area of 483 sq-mm. Some online parallel plate capacitance calculator shows about 6pF for that inch of length at a plate separation of 1mm (which is huge).The cling-wrap nowadays is PVC (dielectric constant of 4) and 0.5mils (0.012mm) or less thick, which will bring your capacitance/inch (at 3/4" width) in the order of 1nF. But:- a risky proposition to use a single layer of cling-wrap - easy to puncture during manipulation and hard to maintain the mechanical integrity in exploitation - squeeze the capacitor a bit and you may finish cutting through the film.- more important - you aren't interested in increasing the capacitance of the capacitor itself - let it be zero for all you care. Rather you are in...see more »Plastics have a dielectric constant above 2. One inch of 3/4 plate will get you an area of 483 sq-mm. Some online parallel plate capacitance calculator shows about 6pF for that inch of length at a plate separation of 1mm (which is huge).The cling-wrap nowadays is PVC (dielectric constant of 4) and 0.5mils (0.012mm) or less thick, which will bring your capacitance/inch (at 3/4" width) in the order of 1nF. But:- a risky proposition to use a single layer of cling-wrap - easy to puncture during manipulation and hard to maintain the mechanical integrity in exploitation - squeeze the capacitor a bit and you may finish cutting through the film.- more important - you aren't interested in increasing the capacitance of the capacitor itself - let it be zero for all you care. Rather you are interested in the "stray capacitance" resulted from the electrostatic field closing through the surrounding medium. So, instead of mounting the plates face-2-face, a better approach would be to align them side by side - just glue them on a strip of plastic as close as you can and then apply an as thin water-proof insulator as you can. Strip of plastic - mmm - a plastic ruler the kids use for school (may dissolve when insulating or gluing the bars)? For longer lengths or a bit higher resistance to solvents in the insulation coating - a segment from a PVC rainwater pipe that you cut at length, put an Al-foil on top and flatten you with the clothing iron set just a tad above the nylon/polyester setting?

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  • Capacitor Tester / Capacitance Meter

    "should I dunk the whole probe in epoxy resin to waterproof the sides of the circuit board where it was cut?" Definitely not, you'll kill the sensitivity by increasing the thickness of the dielectric. If you want to try insulating the sides, try applying the insulation on a narrow strip along the edges. What I can tell, I had the same experience with the DIY probes I insulated by repeated dip-coating in polystyrene solution - the sides where insulated and yet the steady state was attained only after 4-6 hours (the fabbed probes stabilized a bit sooner, but not much sooner). I suspect some sort of phenomenon in which the air trapped in micropores dissolves in water or actually reorientation of the water dipoles inside those micropores may play a rle. With a thin coating, you ha...see more »"should I dunk the whole probe in epoxy resin to waterproof the sides of the circuit board where it was cut?" Definitely not, you'll kill the sensitivity by increasing the thickness of the dielectric. If you want to try insulating the sides, try applying the insulation on a narrow strip along the edges. What I can tell, I had the same experience with the DIY probes I insulated by repeated dip-coating in polystyrene solution - the sides where insulated and yet the steady state was attained only after 4-6 hours (the fabbed probes stabilized a bit sooner, but not much sooner). I suspect some sort of phenomenon in which the air trapped in micropores dissolves in water or actually reorientation of the water dipoles inside those micropores may play a rle. With a thin coating, you have higher sensitivity and, of course, no free lunch (or drinks) - the price to pay is sensitivity to trapped air too.

    See the adventures of diy_bloke in the capacitive probes land - depending on the application, it may be the quality of the coating that matters more than the geometry of the electrodes - http://www.instructables.com/id/Comparison-of-Capa...> invoke the Druidic Gods of Capacitance (or Google) to help me get a more responsive probe.My assessment based on my prev conjuring of the same (a bit over a year ago) didn't show anything in this regard - perhaps the Aboriginal totem animals deal in some other ways with the presence of water. By all means, all the best luck to you (and please keep me posted if you run into anything interesting) - but... be prepared to switch the approaches if you run out of time without getting to the bottom of it.If you are still toying around the "water le...see more »See the adventures of diy_bloke in the capacitive probes land - depending on the application, it may be the quality of the coating that matters more than the geometry of the electrodes - http://www.instructables.com/id/Comparison-of-Capa...> invoke the Druidic Gods of Capacitance (or Google) to help me get a more responsive probe.My assessment based on my prev conjuring of the same (a bit over a year ago) didn't show anything in this regard - perhaps the Aboriginal totem animals deal in some other ways with the presence of water. By all means, all the best luck to you (and please keep me posted if you run into anything interesting) - but... be prepared to switch the approaches if you run out of time without getting to the bottom of it.If you are still toying around the "water level sensor", a suggestion: 1. use an as-long-as-your-depth cap (something like two parallel strips of Al-foil pasted on a piece of plastic and water-proofed after). You will have, say, +/-10% error on the level, but it should be a linear dependency between the submerged part of the probe vs reported capacitance. That will be "informational purposes only".2. use one small probe to detect the max level and prevent overflow (shut down the inlet pump or something) and another one for the "low level" (start the pump) - you may use something like the one I sent you or the simpler ones diy_bloke is using. Since they'll be used as "threshold detector", the absolute value won't matter too much, as long as the "submerged/above water" signals are distinct enough (at they are distinct enough for the ones diy_bloke and me are using)Actually, the minimum necessary would be point 2. Point 1 may even be implemented as some other threshold-type of probes spread along the monitoring depth (instead of a continuous one) - a smaller size will make the task of waterproofing them easier.

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  • acolomitchi commented on mikey77's instructable How To Make Your Own Sugru Substitute2 months ago
    How To Make Your Own Sugru Substitute

    > 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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  • acolomitchi commented on lonesoulsurfer's instructable Portable, Solar 12V Battery Pack3 months ago
    Portable, Solar 12V Battery Pack

    > 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 ...see more »> 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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  • acolomitchi commented on shahrokhani's instructable A DESK TOP EVAPORATIVE COOLER3 months ago
    A DESK TOP EVAPORATIVE COOLER

    What else to say than... really cool!Thanks for sharing.

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  • Automatic watering system with capacitive probe and Arduino on the cheap (and I mean it)

    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 r...see more »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.

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  • Automatic watering system with capacitive probe and Arduino on the cheap (and I mean it)

    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....see more »> 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.

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  • Automatic watering system with capacitive probe and Arduino on the cheap (and I mean it)

    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.>...see more »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.

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  • DIY Homemade Constant 5V Voltage Source

    > 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.

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  • DIY Homemade Constant 5V Voltage Source

    > 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 &...see more »> 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...?

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  • DIY Homemade Constant 5V Voltage Source

    > 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?

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  • acolomitchi commented on cgendron's instructable Making Graphene4 months ago
    Making Graphene

    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.

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  • acolomitchi commented on diy_bloke's instructable Comparison of capacitive soil probes4 months ago
    Comparison of capacitive soil probes

    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.

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  • acolomitchi commented on diy_bloke's instructable Comparison of capacitive soil probes4 months ago
    Comparison of capacitive soil probes

    > 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 10x...see more »> 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...see more »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).

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  • acolomitchi commented on dagorald's instructable An improved moisture sensor5 months ago
    An improved moisture sensor

    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 o...see more »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)

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