DIY LED Strobe.

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
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JR.
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Re: DIY LED Strobe.

Post by JR. »

Got the cheap LED DJ strobe in... Looks like it uses a hot chassis with 555 timer driving 21 LEDs in series. So I'll need to be careful. I have an opto triac left over from my DIY heater last winter.. Looks like i may need a different part since I want to cycle faster than 60 Hz.

JR
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ricardo
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Re: DIY LED Strobe.

Post by ricardo »

Having the strobe at a slightly different frequency allows you to see smaller movements as the patterns move. This is from using a B&K strobe to look at speaker cone breakup. But all this only works at 'low' frequencies.

To look at treble units you need a laser doppler interferometer which is the same idea at HF :lol:
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JR.
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Re: DIY LED Strobe.

Post by JR. »

Yup the vibration modes in drumheads are very similar to speaker breakup.

FWIW I already know what my lug mode looks like
To clear lugs I set up this standing wave and synchronously detect the max output to be under the mic... When I adjust the lug tension the standing wave rotates CW/CCW relative to the mic and speakers.

So i can already measure very precisely what is going on, I just want to make some hip light show/visual effects to amuse drummers.

I may roll my own power supply to drive the DJ strobe... Instead of 21 LEDs in series i may drop it down to 7 to get the voltage more manageable. I don't like the concept of messing with hot chassis around my computers.

JR
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tubegeek
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Re: DIY LED Strobe.

Post by tubegeek »

I feel like you are working a little too hard to amuse drummers - don't they usually amuse easier than that?
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JR.
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Re: DIY LED Strobe.

Post by JR. »

tubegeek wrote:I feel like you are working a little too hard to amuse drummers - don't they usually amuse easier than that?
Apparently being able to make their drum sound better isn't enough for many.

I suspect the amplitude of the drumhead will be too small to make a good visual... I may need to amp up the power I'm sending into the drumhead too...

Yes, probably too much work for too little bennie.

JR
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JR.
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Re: DIY LED Strobe.

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Inching forward... this morning I removed the guts from the cheapo DJ strobe, except for the LEDs... They used 21 in series with a 135V hot chassis power rail. I have reconfigured them into two banks of ten so I can bang with a lower PS. I rolled a quick 50V rail from an old +/-15V transformer using both windings in series half wave. From a quick test through a 20 ohm R the LEDs get blindingly bright so if this is going to work I'm getting closer.

My lawn is calling me right now, so later or tomorrow I'll hook up my 60V switching mosfet to this and see if I can see anything...

I probably need to increase the audio power I'm driving into the drumhead to get more vibration amplitude. Right now I'm driving those speakers in series from 5-6V rail... If it put the speakers in parallel I will get a bunch more power (until my driver IC goes toasty. :roll:

Later...

JR

PS: Note the high voltage cap I used to make my 50V PS was one of a bunch of 100V caps I bought to make floating rail mic preamps, but never did.
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JR.
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Re: DIY LED Strobe.

Post by JR. »

OK, another chapter in my love/hate relationship with microchip... I like the parts but hate the documentation/support.

Yesterday I got bit by a quirk in the software compiler (I think), but something that was working stopped for no apparent reason.

I was re-purposing one of the micro pins that is used for programming and real time debugging, to drive my mosfet switch to flash the LEDs. This was working as expected last week... Since I bring the programming pins out to my programming header/dongle it makes it easier to connect external strobe LEDs. Well like i mentioned it inexplicably stopped working, not just the LED driver, but the normal version of the software stopped working too (it worked in debug mode, while still attached to computer but not release mode by itself.. )

The thing I dislike about debugging things digital is that there are too many variables, problem could be PS collapse, bench interface cables, whatever, things all too possible in the prototype environment. I didn't discover until later last night that the software compiler was messing up when I told it that I wanted to use a programming port as an output. It didn't care before, but now just started to care. Late last night I discovered that if I moved the instructions where I initialized the port as an output down later in the software code body, it started working again... arghhh. So now I'm where i should have been yesterday.

I am noticing too much brightness variation for the length of time that I pulse the strobe. Most real strobes discharge a cap so you just turn them on, not off. I need to figure out a good steady time interval... Now I use a too short on interval, but I can see occasional brighter pulses if some interrupt hits during the short on time. I have several different interrupt services so I need to pick one that is short enough and perform my flash during one of those intervals or disable the interrupts during my flash interval. I don't want to make it too long as that could smear the imaging, but for now it's too short (uSecs not mSecs) .
======

My low voltage lawn lamp just arrived.. only two LEDs so no hurry to test it (vs. 20 LEDs now). I like the form factor and beam focus (like a flashlight). Looks like it might make a good trouble light for the car if I make an adaptor to plug into my cigarette lighter.

JR
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JR.
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Re: DIY LED Strobe.

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I am ready to stick a fork in this... I got the strobe pretty bright and well behaved but see no standing wave.

Then I converted my two speakers from series (16 ohm) to parallel (4 ohm) for more amplitude, and my battery eliminator PS crapped out from the extra current, so I beefed up the power supply and still no love.

Last attempt was to put this on a 22" bass drum which should be higher amplitude due to larger compliance from larger head but again no useful visual.

So time to put this on my heap of broken dreams. The electronic part of it works, just the physical real world is not playing along. It might be interesting to use to look at LF loudspeakers or whatever but I'm now of the judgement that actual drumhead vibration is too small to easily see.

Oh well...live and learn.

JR
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mediatechnology
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Re: DIY LED Strobe.

Post by mediatechnology »

I still think you need to play with a laser diode or laser line generator. My 2 cents.
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JR.
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Re: DIY LED Strobe.

Post by JR. »

There is a laser based drum trigger, and if the drumhead was higher than the rim system (like tympani drums) a straight laser shot flush with the top surface could reveal the small excursion. I could bounce a laser off the drumhead at an angle and amplify the motion.

I had a visual image of what I wanted to realize and reality did not accommodate me.

JR
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