# Is it OK or destructive to thin out the wafer of photoresistors?

The standard type, with a white to vermillion round head. I have this project nagging in my head. My battery of power banks is very tightly packed and protected that while I can pull one out of the stack I need a lot of ef-for-T to LIFT any of them and see in the LCD screen how much it was filled when I leave before completely recharging them. When the power bank finishes recharging, the LCD display goes off; while the bank is charging it displays a percentage. So the idea is simple: use a sensor (I think this is patentable). But I do not want a one-to-one correspondence between sensor and LCD segments, nor need a fancy camera like sensor because it is more than one bank (incidentally, the top one has its LCD display broken, disconnected). Then the logic becomes a little bit devious... For one figure charges, below 10%, I can take the bank to be as good as empty, so I only have to check whether it turned on or if it is off, like when the transformer self unplugs. When it is charged all the way up to 100% I have only one meaningful digit, so I can ignore the other digits and only check for light on or off; the LCD remains on for a while after reaching 100% then goes off. I only have to detect the middle figure to be done. I assume maximum glow is reached at 88%, which gives me a figure on the 80s if I do not detect the first figure. 80% or above is OK to say the bank is charged. I suspect 8 and 0 may get diffusely confused, but it does not matter because there is no 0digit% output and the second position can only be zero if charge is at 100%. Then 1 and 7 may also be confusable but it does not matter because if it is 7x% it will soon reach 80% so I ll know in a few minutes if the charge was low in the 10%s because 2x% will not glow as much as 80%, or if it was in the 7x% range and already reached an OK 80%. 3 and 5 may be confusable among themselves, but 4 and 6 may be distinguishable if the sensor can discern one segment differences; also 2 and 4 may be confusable. In all these cases I only have to wait for so many minutes to detect the change in glow and determine on what percentage range the power bank is. I have to go empiric on this one, but for 20%/40% I can say the bank is in middle low charge, for 30%/50% I can say it is in the middle range charge, for 60% i can say it is in the high charge range and 70% is again a matter of waiting for a few minutes. Not much, since partial charges will fall on average on 5% so I have to wait only for a 5% change to determine the range and then increasing/decreases in glow can only happen in one way for specific x0% digits. In general I would not know exactly the charge level but this depends on whether the sensor sensibility can or cannot detect specific digits and I can safely ignore single digits because in terms of powering they make little difference, the real important distinction is betwen completely empty and some charge (I would at least be able to turn on a spent device in the worst power emergency).

The real problem is then not the circuit design nor the programming logic, but the physical installation of the sensor. I may use from two to four photoresistors, one or two for each digit, making a total of six to twelve arduino photoresistors. It would be straight if there was enough space above each power bank, but when stacked the standard photoresistor is just too bulky and may even break th LCD! Thinning them down to a slim wafer seems OK with some padding, which is needed anyway to control the glow input, but I am NOT SURE if the standard photoresistors would lose sensibility or even stop working altogether if I thin them out!! The effort is not simple, they are way too small to hold with bare hands and the power tool may be too forceful for a small clamp, but anyway... I know of no other photoresistor brand or type and I do have a few of these at hand. So I want to know if anyone has had the experience of if there are a priori consideration why this is or is not possible before doing the effiort.

See that back-and-forth pattern on the photoresistors?

That’s the photosensitive material. If you interrupt that trace, it won’t work anymore.

Also, you want to keep it potted, as the internal material is toxic (it’s some cadmium compound I think).

Photodiode or phototransistor will probably get you better results.

But using that is silly. You’d need to have the sensors arranged specifically for each kind of power bank - meaning you’re sort of wedded to a specific power bank - at which point, modifying the power bank is probably an easier route.
Just monitor the current going into each power bank The current they draw goes down dramatically when they’re full (to the tens of mA to keep the LEDs on)

I think the approach is wrongheaded, and likely inferior to other routes towards acheiving the same goal. I doubt it’s patentable - I’m sure you’re not the first person to try to detect indicator lights with a light sensor to automate non-automatic devices.

Hi, Just what photoresistors do you have??

I use a lot of THIS: type. These are 0.105 inch thick, so if they were on a 0.031 pc board that would be 0.136

THE question: How thick is Too Thick?

WhatIf you used plastic fibre optic fibers epoxied on the display or a thin clear sunstrate, to external photoresistors? Hmmm...

That's a very long paragraph.

My only question is why photoresistors and not photodiodes or phototransistors?

DrAzzy: That's the photosensitive material. If you interrupt that trace, it won't work anymore.

The photosensitive material is in the gap between two metal electrodes, I think its a very short wide trace, not a long thin one as your comment implies.

It sounds as if you’re trying to obtain an image from many photo detectors… or have I misunderstood your very long post?

if so, ccd array based camera imaging devices do exactly that - not that I’ve used them - might that be a simpler (trhough not trivial) approach…?

regards

Allan

Oops! Yes, it is this TYPE of transistor, and for all the ones I have thin is just too thick.

No, I do not try to get an image, that would need decoding, but I do want to sense the digits in the LCD display. And I need to sandwich these sensors along with the power banks: sBsBsBsB. The on pushbutton is raised about two or three microns over the case so it is convenient the sensor be somewhat thicker as it would relieve pressure on the pushbutton (it selects voltage, it sometimes activate alone out of pressures while moving), and no, it is not possible to modify the aluminum case, I am even coping with a broken LCD giving no lecture but only some light when on.

Only real problem in using optic fibers is I have none! And actually have no idea where to get them either, have already sought them and found no good alternative. Tried a cheap color threads lamp ones and no, they were just too opaque to be useful. Photodiodes and phototransistors are just too BIG for the thin layer between power bank displays I need. Normally those batteries are pressed one against the other even violently, anything bulky would break them, as it already happened.

Oh, patentable? Sure. I d be getting a three digits level lecture from only TWO small sensing nodes and without forming an image reach a useful conclusion. I only need glare lectures, and it would work with every LCD screen with three big segmented digits! Not that it would be useful beyond my somewhat improvised stack but still the logic to achieve an off/low level/middle level/high level/OK/finished scale is very nice and programmatically efficient.

DrAzzy: Also, you want to keep it potted, as the internal material is toxic (it's some cadmium compound I think).

Do you know more of the internal structure? You imply thining it down to half width would leave a toxic surface exposed, when all I was fearing is these components need all the grounding they can get to achieve their effect. It also seems the trace is deep and goes all the way down to the back so you cannot simply thin and resolder.

DrAzzy: Just monitor the current going into each power bank ;-) The current they draw goes down dramatically when they're full (to the tens of mA to keep the LEDs on)

Hey! Not that easy! I admit these banks are losing charging power (sic), so I no longer have a half week or more days of , it is now like a weekend at full load, whole day computing sessions, so now I truly need to know up to what percentage level banks are charged at to calculate how much time I will get. To monitor the current I d need a jack passthrough for each bank at least, meaning finding one that fits and I can intervene with my monitor! If I can use two photoresistors for each power bank, one nano can provide all the computing power to monitor three or four banks and inform their state. I can leave power input cables plugged in but not out cables plugged in because these last ones drain the battery quickly even if not in use by gadgets. I would have to monitor current on both input and output! Other than that the bank stack is hidden and in darkness, so any light detected becomes information at a very cheap cost.

Hi,

The standard type, with a white to vermillion round head. I have this project nagging in my head. My battery of power banks is very tightly packed and protected that while I can pull one out of the stack I need a lot of ef-for-T to LIFT any of them and see in the LCD screen how much it was filled when I leave before completely recharging them. When the power bank finishes recharging, the LCD display goes off; while the bank is charging it displays a percentage. So the idea is simple: use a sensor (I think this is patentable). But I do not want a one-to-one correspondence between sensor and LCD segments, nor need a fancy camera like sensor because it is more than one bank (incidentally, the top one has its LCD display broken, disconnected). Then the logic becomes a little bit devious... For one figure charges, below 10%, I can take the bank to be as good as empty, so I only have to check whether it turned on or if it is off, like when the transformer self unplugs. When it is charged all the way up to 100% I have only one meaningful digit, so I can ignore the other digits and only check for light on or off; the LCD remains on for a while after reaching 100% then goes off. I only have to detect the middle figure to be done. I assume maximum glow is reached at 88%, which gives me a figure on the 80s if I do not detect the first figure. 80% or above is OK to say the bank is charged. I suspect 8 and 0 may get diffusely confused, but it does not matter because there is no 0digit% output and the second position can only be zero if charge is at 100%. Then 1 and 7 may also be confusable but it does not matter because if it is 7x% it will soon reach 80% so I ll know in a few minutes if the charge was low in the 10%s because 2x% will not glow as much as 80%, or if it was in the 7x% range and already reached an OK 80%. 3 and 5 may be confusable among themselves, but 4 and 6 may be distinguishable if the sensor can discern one segment differences; also 2 and 4 may be confusable. In all these cases I only have to wait for so many minutes to detect the change in glow and determine on what percentage range the power bank is. I have to go empiric on this one, but for 20%/40% I can say the bank is in middle low charge, for 30%/50% I can say it is in the middle range charge, for 60% i can say it is in the high charge range and 70% is again a matter of waiting for a few minutes. Not much, since partial charges will fall on average on 5% so I have to wait only for a 5% change to determine the range and then increasing/decreases in glow can only happen in one way for specific x0% digits. In general I would not know exactly the charge level but this depends on whether the sensor sensibility can or cannot detect specific digits and I can safely ignore single digits because in terms of powering they make little difference, the real important distinction is betwen completely empty and some charge (I would at least be able to turn on a spent device in the worst power emergency).

The real problem is then not the circuit design nor the programming logic, but the physical installation of the sensor. I may use from two to four photoresistors, one or two for each digit, making a total of six to twelve arduino photoresistors. It would be straight if there was enough space above each power bank, but when stacked the standard photoresistor is just too bulky and may even break th LCD! Thinning them down to a slim wafer seems OK with some padding, which is needed anyway to control the glow input, but I am NOT SURE if the standard photoresistors would lose sensibility or even stop working altogether if I thin them out!! The effort is not simple, they are way too small to hold with bare hands and the power tool may be too forceful for a small clamp, but anyway... I know of no other photoresistor brand or type and I do have a few of these at hand. So I want to know if anyone has had the experience of if there are a priori consideration why this is or is not possible before doing the effiort.

Sorry but needed to be spread. Tom...

Hi,

Are you trying to read the individual digits on an LCD display with LDRs? So you can get a voltage or state of charge reading in an Arduino?

Tom... :o :o :o :o PS I'm not sure if we have a language problem here, but syntotic can you go back and reread your first post. Can you tell us your electronics, programming, arduino, hardware experience?