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flashing LED badges

Discussion in 'Crafts and Cooking' started by SamP20, 4 June 2015.

  1. SamP20

    SamP20 A partridge in a pear tree

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    So I had this idea to make some pony themed flashing LED badges. I did a quick render in blender of Rainbow Dash's and Rarity's cutie marks, and am quite happy with the result:
    rd_highres.png rarity.png
    Also animated versions here:

    The badges would probably be constructed like so:
    construction.png
    I'm still trying to figure out the best way to make badges with multiple sections. One option would be to use a single sheet of clear plastic, but only place the decals/circuit board where the sections are. Thin wires would still be needed between the sections for power.

    Do you think this is something I should continue working on? I suppose I could even do commissions, if people wanted, once I've made one successfully.
     
    #1 SamP20, 4 June 2015
    Last edited: 5 June 2015
    Wisdom Pen, Dax, Stormblaze and 3 others like this.
  2. Hot Wings

    Hot Wings Honorary Pony

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    You should continue doing this, it looks great! :D
     
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  3. MCtoastie

    MCtoastie Element of Elements

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    These look awesome, they would be a nice accessory to have for BUCK :D
     
  4. Crow0785

    Crow0785 Kernow Broba

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    Keep it going, they look great.
     
  5. SamP20

    SamP20 A partridge in a pear tree

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    Thanks. I had a play with an RGB LED fading through various colours behind Dashie's cutie mark:

    Cheap paper, and my camera don't do it justice though. I don't think the colour changing works well in this instance anyway as the individual red, green and blue colours don't mix very well. I still think plain white LEDs are the way to go once I get hold of some.

    Also this whole flashing cutie mark thing reminds me of the cutie map. Maybe I should do entire ponies too but with a single flashing/fading LED :D
     
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  6. Ripp_

    Ripp_ * You Hug the Pig

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    Badges look rather large. I guess they need to be large enough to hide the electronics.
    you could try going surface mount then you wouldn't need holes in the board they would proably be thin enough.
    If you wanted to go mad some neo pixels, but each badge is far too small for that
     
  7. SamP20

    SamP20 A partridge in a pear tree

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    The sizes aren't actually final yet. Hopefully surface mount will allow me to make things smaller :)

    Ideally I would like to keep to a single sided board with mostly surface mount. With the requirement to have the battery accessible (probably with a holder like this: http://uk.farnell.com/keystone/3006/coin-cell-battery-holder/dp/1702640), it seems easier to have all the components on the back, but place the LEDs upside down so they shine through holes in the board. Alternatively I could mount the LEDs normally and use a through hole battery holder to keep the battery accessible like this: http://uk.farnell.com/multicomp/ch25-2032lf/battery-holder-dip-20mm/dp/2064715. Actually this may be the better option as it saves some space on the copper side of the board allowing more room for the microcontroller and other components.
     
  8. Ripp_

    Ripp_ * You Hug the Pig

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    Is a microcontroller really nessesery for this few leds?
    Just some fancy 555 work surly
     
  9. SamP20

    SamP20 A partridge in a pear tree

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  10. Ripp_

    Ripp_ * You Hug the Pig

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  11. electrokitty

    electrokitty Coffee Enthusiast

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    Yay electronics! Looks like a nice project, I'd be interested in helping in any way if you'd like. I've got experience with electronics design and development and also surface mount technology.

    Might be nice to get the cutie marks laser cut out of acrylic or something so the LED light diffuses through them better. Also you could probably house the electronics in a very small cheap PCB mounted underneath fairly easily. Perhaps something like this coming out of the PCB with a boost converter if you wanted it lit along the whole length.

    This could be a really simple design though, there's an even smaller, cheaper and cuter µcontroller which is the Attiny4. Comes in a nice little sot-23-6 package and supports PWM. The only external components you'd need is some breakout to a header for the programming of the thing, a pullup resistor on the reset and any current limiting resistors for the LEDs (and a decoupling capacitor probably wouldn't go amiss too). The Attiny4 can be powered over a wide range of voltages eliminating the need for a regulator, has an internal clock eliminating an external oscillator and the I/O pins can drive a decent amount of power which should be enough for a few small LEDs without having to use and transistors.
     
  12. Ripp_

    Ripp_ * You Hug the Pig

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    A LAZER CUTTER
    the person from the hackerspace was just here going mad about how they jsut got one
     
  13. SamP20

    SamP20 A partridge in a pear tree

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    Thanks for the offer. I should be okay for now, but I'll let you know if I need anything. Of course, you're still free to suggest any ideas or point out my mistakes :p

    That was the intention from the beginning. The badge would be acrylic with a decal applied to the top, and the PCB below. I think the Youtube video might have distracted from that a bit :p. I would love to own a laser cutter as it would make this so much easier. One day I might attach a laser diode to my 3D printer. In the meantime it'll have to be a manual job.

    Even though it's simple I've realised there's still a lot to consider. For example for power I've decided upon a 4.5V supply since the LEDs drop roughly 3.3V, and 6V would be too much for the Attiny without a voltage regulator. Then there is the issue of size. 3 AAA cells would be far too large to hide behind most badges. The best compromise I can currently think of for size vs capacity would be 3 LR44/SR44 cells. Designing for a 10mA current draw would only result in about 10-15 hours lifetime (100-150mAh cell). Not quite enough for a 2 day convention. I might be able to get away with 5mA if it's still bright enough, which would double the lifetime. The only way to find out for real is to just buy the parts and try it :)
     
  14. electrokitty

    electrokitty Coffee Enthusiast

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    Ah cool yea, I didn't see the bit about the proposed construction. There's probably various companies that would do laser cutting as a service or if you've got a hackspace or uni nearby that has one you could use. You'd probably need something a lot more powerful than a semiconductor laser for cutting acrylic, laser cutters tend to use gas discharge lasers for increased power.
    Hmm, LR44s are a little on the small side and as you say the current and capacity of them isn't great. Personally I'd probably go for a CR2032 or something like that which is still fairly small but has a higher capacity. You could either use two of them and a low dropout voltage regulator (the ADP1712 is a very nice example) or use one cell with a boost converter (could use a regulator as well but it's probably not worth it for a simple thing like this, and the micro will work across a range of voltages as the battery discharges). There's a whole bunch of boost converters out there so you'd have to have a look at some datasheets to find one which is most efficient at the voltages and currents you'd be using but they're fairly cheap, even with the few external components required. A CR2032 cell would have plenty of spare capacity to power the boost converter over some LR44s anyway.
     
  15. SamP20

    SamP20 A partridge in a pear tree

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    I did have a look at the CR2032 batteries, but I found out they had quite high internal resistance. It seems the maximum discharge current is around 3-4mA. That being said they might still be okay. two cells in series and a buck converter to 3.5V (just above the LED voltage drop) might reduce the current enough. 5mA at the LEDs would be reduced to 3.0mA at the cells (maybe a little more due to losses). It's a close one.

    I think before I go any further I should determine what current I can get away with at the LED (assuming only one lit at a time), and then design the power supply with that requirement. Thanks for the suggestions so far though :)
     
  16. SamP20

    SamP20 A partridge in a pear tree

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    Yesterday I ordered some white LEDs and a few other bits from Farnell. Next day delivery when you order before 8:00pm is amazing :D

    So I tested to see whether 5mA was enough to get some decent brightness. I think this photo is conclusive (my camera actually under-exposed the image slightly because of the light):
    test 5mA.jpg
    With the final design the pieces would be more closely sandwiched together, so the light should be a little less diffused (and I'll also be using decal paper, instead of plain paper, which I think is a little more glossy).

    This is how I managed to test it:
    LED test wires.jpg
    I was going to test another LED, but I really can't be bothered to try and solder wires onto the damm thing. I can hardly see it!
    really small LED.jpg

    Next stage is to design the power supply and order more parts. I also need to figure out what size I want the badge to be and how to attach it to clothing. One method would be to attach a safety pin to the circuit board using two loops of wire.
     
    #16 SamP20, 11 June 2015
    Last edited: 11 June 2015
  17. Arc Light

    Arc Light Caffeine levels discharging: 68%, mood lighting

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    Exactly how are you planning to lay out the PCB?

    I was looking at 555s earlier this year and made this on a bread board
    https://www.dropbox.com/s/pil86js2u66hj8c/2014-11-14 15.01.29.jpg?dl=0
    (Ignore the excessive resistors, I was playing about with it)

    Now with your Micro being roughly the same size at the 555, your still going to have the rough shape but unless you get an actual SMT line to solder your (random guess) 0805 chips to the board, your gonna have a heck of a time getting them on yourself.

    Through hole wise for one LED is roughly something like this. (untested as I didn't purchase the required caps and resistors to correct the dimensions and viability, I'd probably make it a little bit bigger)
    https://www.dropbox.com/s/cza0nuft64zyw2p/2015-06-11 17.11.50.jpg?dl=0
    (laid out on a sticky note with a ruler for scale, dimensions the same as the image below)
    555 circuit.PNG

    It's not massive to do with 555s and through hole but it would be cheaper and probably a lot more viable. I planned to wire in a battery snap connected to a 9V battery which was going inside the box with the board and the LED would pop out a hole at the top.
     
    #17 Arc Light, 11 June 2015
    Last edited: 11 June 2015
  18. SamP20

    SamP20 A partridge in a pear tree

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    0805? They're massive! Joking aside, when I worked at Broadcom for a year I was soldering mostly 0603 components, and occasionally 0402 (I used a microscope to do those though. They were small :p). For this project I'll keep to 0805 or larger components. The LEDs I'm planning to use are similar size to 1206 components (3.2mm x 2.8mm to be precise).

    The circuit is going to be something like below, although with some extra power supply circuitry (boost converter etc), and a switch:
    schematic.png
    The layout will change for each different badge to match the shape. I haven't quite got that far yet though.

    I have to admit, what started off as a simple idea is actually a really interesting engineering challenge :D

    Edit: I forgot to say that you've done a good job squeezing all of your components into such a small area :). If you wanted to you could possibly move the 470k resistor slightly closer to the 555. There's also the option of placing components vertically. Here's a design I did a while ago which controls an RGB LED:
    board2.png
    Some of the resistors such as R7 and R5 are vertical.
     
    #18 SamP20, 11 June 2015
    Last edited: 11 June 2015
  19. Arc Light

    Arc Light Caffeine levels discharging: 68%, mood lighting

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    Wow... Your a braver man then I am XD but I guess your probably IPC trained to solder SMT components so that's a plus ;)
    Seeing rework on boards at my work place was scary, your going to skip the SMT line and do it all manually ^_^

    It does look like a very fun engineering problem. You'll definitally need different designs for each badge. Though it does sound like your boards aren't always going to be rectangles (RD badge with SMT LEDs will need a specific shape if the LEDs are to be spread throughout the shape)

    Very nice design for the RGB LED, I hadn't thought about vertical through hole resistors before but that would be very useful if there's the free vertical space ^_^

    Thank you, this was just me playing about on KiCAD, as a MEng Mechatronics student, I should at least try and build the most basic of circuits in the world. Practical over theory any day. :p
     
  20. SamP20

    SamP20 A partridge in a pear tree

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    A quick update for those following along. I haven't been doing much work on the badge design lately, but instead have been making the tools required to expose and etch the circuit boards. These will be used for other projects too.

    My first tool is a UV exposure box. I have an array of 84 ultraviolet LEDs consuming about 6 Watts in total. You definitely don't want to stare directly into it (I would go as far as wearing sunglasses or other eye protection for regular use):
    uv exposure box.jpg uv exposure box off.jpg
    I turned it on in my dark room and noticed everything white was glowing :D.

    My other tool is a bubble etching tank made from a cereal storage container and an aquarium air pump. I plan to etch the boards using Hydrochloric Acid+Hydrogen Peroxide based on this instructable Stop using Ferric Chloride etchant. Here's a photo of testing with water:
    bubble tank.jpg

    I have had a little more thought about how to power the device. I am currently thinking about 2 CR2032 lithium cells with a buck converter. It's on the limit of what the cells can handle, but ballpark calculations suggest about 40 hours lifetime, the best so far without going for anything larger. I also noticed they are really cheap online. I found a pack of 10 Maxell cells for about 20 pence each on eBay which makes high street prices look ridiculous! I think that is a small enough price to pay whenever you want to show off ;)
     
    #20 SamP20, 23 June 2015
    Last edited: 24 June 2015
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