a bit of PWM anyone?- Mtbr.com
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  1. #1
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    a bit of PWM anyone?

    hey guys,
    I think its about time i get round to building my first light

    Im gonna try and keep it simple...ish, well atleast compared to some of the beasts ive seen on here!

    Gonna go down the diy dinotte style route as it seems quite tried and tested and most of all simple on the mechanical side of things which is my weakpoint.

    Now on to the electronics ive bought some R2s and some 800ma single mode drivers off dx and ive had a little play and the first thing i say is my god there bright! but after thinking about it alot ive decided to try and add some dimming, i think ill try and do this by adding a 555 timer PWM circuit to the input. ill keep the input at about 144Hz but vary the duty cycle. would a 7135 chip in the driver circuit work at this frequency? Has anyone tried this kind of thing? hopefully i should be able to get a output from 0-100%ish giving me unrivaled controlability!

    Ive thought about using a potential divider with a potentiometer but i rekon this would be to in-efficient so probs not best in the long run.

    Also where do people get waterproof potentiometers from?

    Well I hope my ramblings are decipherable after all its 4:45am here! man I should be getting to bed

    Night guys!

  2. #2
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    39 views and no reply? come on guys!

    Well in order to a bit more interest i thought id post a nice little picture of my design, it involves fitting the driver board between the led pcb and the back of the optic, ive not seen any1 else try this, is there a reason? like the heat build up will be to high? will i need to sink the driver to the case?

    am i being optimistic trying to fit it in the head of one of these?
    http://www.dealextreme.com/details.dx/sku.46

    Behind the LED allows for a 12mm length slug with 25mm diameter will this be enough for 800ma?

    I was planning on potting the electrics with something like this
    http://www.rapidonline.com/Tools-Fas...compound/30053
    does anyone know how well it conducts heat?

    Also for "glueing" the slug in what is the thermal conductivity of chemical metal?

    Sorry about all the questions, im a complete noob at this

    now for some pretty pictures

    http://www.flickr.com/photos/[email protected]/3600082685/

    http://www.flickr.com/photos/[email protected]/3600082689/


    hopefully this will allow me to adjust each beam independently vertically


    so what do you guys think?

  3. #3
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    you can put a pot on some drivers, buckpacks come to mind. That would be a better approach than anything you've mentioned, and probably cheaper. People attach the led board to the case for heat sinking.

    The answers to most of your questions are here in the threads about other people's projects.

  4. #4
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    If you have DX 800ma drivers and want to add PWM dimming then you could use a d2flex from taskled: http://www.taskled.com/d2flex.html

    But in the end it would be cheaper and probably more reliable to simply get a bFlex (also from taskled)or a dimmable buckpuck : http://www.ledsupply.com/led-drivers.php rather than adding things to the DX drivers.

    They do cost more than DX (it's impossible for things to cost less) but you generally get what you pay for when it comes to drivers.

  5. #5
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    Hi ElPrez, your design seems pretty ambitious to fit the driver in with the optic. That would require some real micro surgical skill to fit it all, if it is even possible. The vertical adjustment is a good idea in general, but in use, I think you will find that it is simpler to just move the light in whatever mount you are using (if it is a decent mount it should be able to adjust vertically somewhat).

    If you want a simple PWM dimmer, all I can suggest is what I have used, and that is a PIC, specifically a PICAXE. The 08M (don't get the 08 though) can do PWM and is about $3, plus you can use the other pins for whatever you want and build in modes or whatnot. Programming is simple (uses BASIC) with some basic hardware stuff (a serial cable and some resistors), they also have great support online. Just my $0.02.

  6. #6
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    OK, well im glad someone else uses PWM

    Ive got some 16pin pics somewhere (cant remember which type) just cant find em :S
    Whereas Ive got about 20 555 chips and with a pot i think id be able to dim as necessary, and i cant see myself using flashing modes. 555s are chips specifically designed for putting into timing circuits and if it doesn't work Ive not lost anything, so ill tell you how it goes!

    this is the circuit ill be using
    http://www.dprg.org/tutorials/2005-11a/index.html

    Below is what i am used to programming,a pic18lf4520 (in assembler) its just to big 2 put in a torch! and if it gets wet its far more expensive 2 replace

    http://www.flickr.com/photos/[email protected]/3603325619/

    Also Ive managed to fit the driver behind the optic with a little filling on the plastic optic case and a smidgen off the driver (its only 16mm diameter) i just need to get some aluminum bar now, and decide how to affix it into the case, as it is going to be the tail of the light i cant just rely on a friction fit. i thought of just soldering it? or is that a bad idea and should just use chemical metal?

    thanks for all the help!


    By the way, the reason im playing with all this instead of just spending money on a new driver is because i already have these drivers and most of the components, and wheres the fun if everything is easy!

  7. #7
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    Thanks for the link, that looks pretty cool. Can you post a pic of how it all fits in there? I would like to see how it all gets in there. Are you needing a way to fix the driver or the star to the case? If so, you can probably just get some thermal adhesive such as this stuff - or the cheap stuff they sell at DX:

    http://www.arcticsilver.com/arctic_s...l_adhesive.htm

    I have used this stuff:
    http://www.dealextreme.com/details.dx/sku.4579

  8. #8
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    Heres some pics, and yes it was tricky but worth it i think!

    http://www.flickr.com/photos/[email protected]/3606296974/

    http://www.flickr.com/photos/[email protected]/3606293468/

    http://www.flickr.com/photos/[email protected]/3605470449/

    note i resoldered the driver connections cause i wasnt happy with em but didnt retake a photo so that last one will have to do

    i was meaning about using chemical metal to hold the aluminium slug into the housing
    if you look on those pics theres a 13mm gap behind the star, (is this enough thermal mass) the slug will go there and probably stay in with a friction fit, i just wanna use somethin to firm it up and keep it a bit more water tight. the front will be well and truely potted and sealed with potting compound. (not that theres much space for it)

    Im gonna mount the PWM circuit on the battery pack i think, maninly because a 70p pot is a lot cheaper than any waterproof ones ive seen. and it keeps the head unit super tiny. Im gonna go to maplin tomorrow to get some diodes and then i can start making it

    Now i need to worry about mounting, i was thinkin of bolting into the sides of the case, or maybe just straight into the back of the slug. what do people think, im hoping to make a couple more modules maybe with a diff optic (2 spot 1 flood) but ill see what the beam pattern is like.

    bought some of these anyway
    http://www.dealextreme.com/details.dx/sku.1917

    and these are the optics im using at the moment
    http://www.dealextreme.com/details.dx/sku.1920

    oh and while im posting links, these are the light bodies i cannibalized
    http://www.dealextreme.com/details.dx/sku.46


    Id like to use the torch for climbing/ mountaineering use also, so i need to think of way i can mount this tiny module to an elastic headband (donated from my 1st gen petzl tikka which just doesnt cut it anymore) id probs only use one module and would like some vertical adjustment (stop me blinding my belay partner at every stance! lol)

    well i thinks thats all for tonight installment, tune in tomorrow folks to see what ive got to say

  9. #9
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    Thanks for the pics, they helped me a lot to understand your design, especially the pics of the housing you are going to use. I would try and get an aluminum slug that fits as closely as possible to the ID of the case and then use some thermal adhesive such as arctic alumina or similar to glue it in there. I would bet that 13mm would work OK if can conduct the heat to the outside though the case, which is really the key to cooling any LED. I just built a single Q5 helmet light that has much less than than, but it has enough material around it to work OK.

    Do you think that the PWM signal would be reliable enough mounted on the battery? Maybe it would be better to have the PWM, pot and driver on the battery and just run the output to the light head, that would also simplify getting stuff in there. I think that is how my friend's cateye works.

    Ocean used a similar light body for his MCE light, the knuckle duster, you may be able to get some ideas from his thread here:

    http://forums.mtbr.com/showthread.ph...hlight=knuckle

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