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  1. #46
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    Quote Originally Posted by Stustoys View Post
    See how it goes Bob.
    If it will make it fit, cut the outside track twice, move a resistor and add a wire, you can remove the red area of the CB(those wire saw blades do a pretty good job on CB) . If it would suit the running of the figure 8 wire better, you could move all the cuts etc around 90 degree and remove the bottom section instead.

    Failing that I have more LEDs in the post.

    Stuart
    Hi Guys,
    From the pictures that assembly looks to be a very good fit. It looks as if the LED's are in four strings of three with 470 ohm resistors in series. Looking forward to seeing the finished item.
    Best Regards:
    BaronJ.

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  3. #47
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    Quote Originally Posted by BaronJ View Post
    Hi Guys,
    From the pictures that assembly looks to be a very good fit. It looks as if the LED's are in four strings of three with 470 ohm resistors in series. Looking forward to seeing the finished item.
    Yes four strings of three, though from memory(never a good idea for me) the resistors are 180ohm. As I've mounted them with numbers down you'll have to wait until the replacements turn up to be sure.

    Stuart

  4. #48
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    Hi Stuart,

    Here's an idea that you might consider for Mk2... or Mk3 http://www.instructables.com/id/Simp...-source-20-mA/

    The advantage is that you can dispense with the series resistors, and vary the number of LED's

    Ray

  5. #49
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    Hi Ray,

    Well now that looks handy.
    Would it be easy enough to make the current adjustable with a pot somewhere for dimming and the up max current* so it can run the 12 leds?

    Further to the battery in the arbor plan(or somewhere else close by) I was planning on using one of these

    http://www.ebay.com.au/itm/251536958...84.m1497.l2649
    Which I think would work well with the above to run the LEDs off a AA battery. Would I be right?

    Stuart

    *I guess I really mean Watts?......seems silly to talk about increasing the current on a current limiting supply.

  6. #50
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    Quote Originally Posted by Stustoys View Post
    Hi Ray,

    Well now that looks handy.
    Would it be easy enough to make the current adjustable with a pot somewhere for dimming and the up max current* so it can run the 12 leds?

    Further to the battery in the arbor plan(or somewhere else close by) I was planning on using one of these

    http://www.ebay.com.au/itm/251536958...84.m1497.l2649
    Which I think would work well with the above to run the LEDs off a AA battery. Would I be right?

    Stuart

    *I guess I really mean Watts?......seems silly to talk about increasing the current on a current limiting supply.
    Hi Stuart,
    That device will step up the voltage from a 1.5 volt source but I think you will be disappointed if you expect to draw 0.5 amps from it. However bearing in mind that its only going to power a couple of LED's and that you only have 5 volts to play with you might find that you can't get enough power (note "Power") out of it to light more than 6 or 8 LED's. Consider that 1.5 v into 5 v = 3.3 and the current out, say 0.12 amps. Multiply that by 3.3 = 0.360 amps. Now an AA cell is rated 0.8 amps. That might give you a battery life of a couple of hours and maybe half that at full brightness.

    I'm not saying it won't work but I think you might be better off using a pair of AA's and not bothering with the DC/DC converter. The difference is down to the losses associated with each configuration.

    HTH.
    Best Regards:
    BaronJ.

  7. #51
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    Hi Baron,

    I only need "about" 60mA 5V (maybe less if it turns out some LEDs can go).
    If their numbers are to be believed(I have no idea) one AA is good for 200mA with "high conversion efficiency, up to 96%" (though I wonder if thats when its converting 5V to 5V?)

    My figures went like this

    30mA at 12V= .36W

    2.6Wh* AA/.36W= 7.2hr

    Now of course I've left out some losses and don't really know how accurate the 30mA is to begin with(I assume not bad as its DC??). But even if you only get 3 hours I'd say that's a fair amount of time for a centering scope**.

    It was mostly to do with the space in a 30 taper arbor for the battery. Once the batteries are external...... may as well have a power supply????

    It can only not work

    Stuart

    *I notice the figure I am using for a AA more than three times yours?
    I got my numbers from here..... I have no idea how accurate they are.
    I guess you're talking Carbon-zinc and I'm talking Alkaline?
    http://www.allaboutbatteries.com/Energy-tables.html

    **for home use... it you were using it all day everyday you'd get sick of it soon enough. Then I'd just have to go to a Lipo battery with a charger in the scope storage case

  8. #52
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    Quote Originally Posted by Stustoys View Post
    Hi Ray,

    Well now that looks handy.
    Would it be easy enough to make the current adjustable with a pot somewhere for dimming and the up max current* so it can run the 12 leds?

    Further to the battery in the arbor plan(or somewhere else close by) I was planning on using one of these

    http://www.ebay.com.au/itm/251536958...84.m1497.l2649
    Which I think would work well with the above to run the LEDs off a AA battery. Would I be right?

    Stuart

    *I guess I really mean Watts?......seems silly to talk about increasing the current on a current limiting supply.
    Hi Stuart,

    How do they make that for $1.06 and free postage?... that's just ridiculously cheap. That will boost it to 5V, more volts would be better. You are on the track, Watts is what you calculate, 5V @ 100mA is the same watts as 1.5V @ 333 mA.. Conversion efficiencies are generally around 95% give or take.

    Most AA alkaline batteries are good for around 2000 mAh, if you have a push button so that the light only comes on when you are actually looking through the microscope, then a single AA cell will last a long time, starting with, say 4 hours @ 500mA, let's say you press the button for 1 minute each time you use it, that works out to 4*60 = 240 times..

    What you need to find some more volts. This one, is twice the price... $2.14 ( There goes the budget ) but you'd need 2 AA's or 1x 3.7V Lithium...

    http://www.ebay.com.au/itm/1PCS-XL60...cabf330&_uhb=1

    Ray

  9. #53
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    Hi Stuart, Ray,
    There are a number of ways to look at this, non are inherently wrong. Lets start with the LED's that you intend to use. What is the nominal voltage at the desired current. The real answer is 'how bright is the LED under these conditions and is it bright enough for what I want to do' ? Then you have to decide if you need more than one LED. After this you then have to ask what do I need to power what ever combination you have chosen. At this point you can then determine if the power source chosen is adequate.

    What generally happens is the designer ends up with a compromise between the number of LED and the maximum voltage available. Usually its cheaper to add a battery in a battery powered system or to raise the supply voltage where the power source is effectively unlimited, ie a mains supplied power supply.

    As a common example look at LED torches. Almost invariably three AAA cells and three or more LED. If you take one of these apart you will find that there is a single low value resistor in series with all three LED just to provide current limiting. When the batteries are nearly flat taking the resistor out restores full brightness for a short time. This works only because as the batteries go flat the internal resistance of the batteries goes up causing self limiting of the current.

    Now I agree with you that you are only talking about very short periods of use and that the longevity of the battery is a secondary consideration. If you use those very small cheap LR44 button cells, three in series will provide 20 ma for about half an hour, and the size can be made very small. Ok you can build that lot into a 30 taper very easily if it will do what you want.

    HTH.
    Best Regards:
    BaronJ.

  10. #54
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    Hi Ray,

    I have no idea how they post it for $1.06.... let alone make the thing in the first place. I have no right to expect it to turn up let alone work at that price, but I'm pretty damn sure it will do both.

    I think I see the hole in my plan. Going to 5V is fine, except I'll then need either 12 resistors or 12 current limited supplies to run the 12 LEDs.

    I saw the $2.14 version but its much larger and needs two batteries.. again we get back to not enough room.

    Could I connect the outputs of two of the 5V convertors in series and get 10V? or will I just let the smoke out of something?


    Hi Baron,

    If I change button batteries to get higher V, then I'll lose capacity.

    All my led torchs use a single led with (I assume)PWM to control brightess with 2x18250 1200mAh 3.7v cells. Now if I could make the board Ray linked to to fit, that might be the way to go. But then you are stuffing about with Li-ion(though at $5.12 for 2 batteries and $2.03 for a charger it might be a goer) I liked the idea(if possible) of a AA as most have them laying around.....or you could even borrow one from the TV remote
    Or forget the board 1 18250cell and 12 resistors?

    I dont actually know the specs on my leds. All I know is the unit is for a car, so at a guess I would say it will take 15V or so. They draw "30mA" on 12VDC and have a V drop across each led around 3V(as per normal I should write these things down)

    I think Bobs getting happier about using an external supply all the time.

    Stuart

  11. #55
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    Quote Originally Posted by Stustoys View Post
    Hi Ray,

    I have no idea how they post it for $1.06.... let alone make the thing in the first place. I have no right to expect it to turn up let alone work at that price, but I'm pretty damn sure it will do both.

    I think I see the hole in my plan. Going to 5V is fine, except I'll then need either 12 resistors or 12 current limited supplies to run the 12 LEDs.

    I saw the $2.14 version but its much larger and needs two batteries.. again we get back to not enough room.

    Could I connect the outputs of two of the 5V convertors in series and get 10V? or will I just let the smoke out of something?
    No. They are not isolated supplies.

    Hi Baron,

    If I change button batteries to get higher V, then I'll lose capacity.

    All my led torchs use a single led with (I assume)PWM to control brightess with 2x18250 1200mAh 3.7v cells. Now if I could make the board Ray linked to to fit, that might be the way to go. But then you are stuffing about with Li-ion(though at $5.12 for 2 batteries and $2.03 for a charger it might be a goer) I liked the idea(if possible) of a AA as most have them laying around.....or you could even borrow one from the TV remote
    Or forget the board 1 18250cell and 12 resistors?

    I dont actually know the specs on my leds. All I know is the unit is for a car, so at a guess I would say it will take 15V or so. They draw "30mA" on 12VDC and have a V drop across each led around 3V(as per normal I should write these things down)

    I think Bobs getting happier about using an external supply all the time.

    Stuart
    Hi Stuart,
    Just a guess based on what you have said ! If you have measured 30 mA that equates to 7.5 mA per string. So at 3 volts per led you could get away with 6 LR44 in two banks of three (4.5 V) and 6 led with 12 ohm resistors in series with each one. You might get 15 or 20 minutes of full brightness. Dependent upon how good the batteries are.

    Now 9 LR44 stacked end to end is about the same size as a single AA cell. JAWI You could make a plastic disc with drillings for the battery stack and the leds on a new circuit board underneath.
    Best Regards:
    BaronJ.

  12. #56
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    Hi Stuart,

    Here's an idea out of left field for you... the rechargeable lithium batteries used in electronic cigarettes are small cheap, durable, screw fittings typically 650 mAh 3.7V

    Ray

  13. #57
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    Quote Originally Posted by RayG View Post
    Hi Stuart,

    Here's an idea out of left field for you... the rechargeable lithium batteries used in electronic cigarettes are small cheap, durable, screw fittings typically 650 mAh 3.7V

    Ray
    Hi Ray,
    Now I didn't know about those ! Yes they would make a good power source, also you wouldn't have to throw away as much power in the ballast resistors.

    Good catch.
    Best Regards:
    BaronJ.

  14. #58
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    Ok I'm a little confused.
    Ray are you saying that battery is much different(other than smaller) than the battery I mentioned above?
    Baron are you talking about using Rays battery with one of these? to save on resistors?
    http://www.ebay.com.au/itm/1PCS-XL60...cabf330&_uhb=1

    P.s. I have one of the above on the way.........I might be able to cut the board in half if it ever comes to that.

    Stuart

  15. #59
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    Boys,

    I'm more than happy with an external power source. To incorporate batteries within the confines of a 30 taper arbor would be a challenge because the Isoma has, from memory, a 15mm internally threaded mount. The taper would require some fancy screwcutting to enable the arbor to be dismantled to allow the installation of batteries and associated connectors and wiring. And replacement of batteries would probably require painstaking graticle realignment.

    I reckon I'll be content enough if I can manage the fiddly lathework required to mount Stu's more than adequate LED illuminator.

    A self contained light source for the Marcel Aubert microscopes Stuart and I have is an appealing proposition though.

    BT

  16. #60
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    Hi BT,

    At the risk of going back OT , does the factory supply have a dimmer? (seems like it would be a handy thing to have)

    Making a new one maybe still be easier........Don't know where I got it into my head it used a 12V supply. Is the 3.5V DC?


    Stuart

    5VDC converters turned up today.. they seem to work just fine.

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