PWM LED's in Dereelight DBS

[Matt7337]

This may seem like an unorthadox question, and it will be a long post but flashlight electronics experts please bear with me and read to the end!

I recently acquired a Dereelight DBS (V1) for my collection of flashlights, and have been loving everything about this light since the day i got it. What I really like about it is the 3SD driver that is in it, giving a low, medium and high output as many of you know.

I build high performance bespoke design PC's for a living, largely making them asthetically pleasing as well as having a focus on extreme performance. I recently shone my DBS on low mode onto a computer which was running on the bench in my workshop. Because the light was in PWM mode, the blades on the cooling fans in the PC appeared to be moving slower (Theres a name for this, the "something" effect... can't remember what it is though). Obviously this is caused by the low frequency of the light... creating an optical illusion. You could work out the perceived speed of the blades rotating by: speed of the blades (rpm) divided by the frequency of the light (Hz). With a little fan speed controlling, I was able to make the fan blades appear to stop alltogether, even though in reality they were still spinning at 1000+ rpm.

What I would really like to do now is incorporate this effect into a few PCs which I have recently designed and will soon be manufacturing that use LED Fans mounted behind a mesh front panel/ grill, replacing the standard 5mm waterclear LED's in the fans with my own coloured LED's and controlling them in a similar way that the DBS controls its Cree LED.

I am currently studying Electronics, Communications and Software at university, and at the moment am programming PIC 16F84's, 16F877's and so on, mainly using C but occasionally using assembly code. I asked the guy who teaches us that module if it would be possible to replicate the effect and he says that a 16F84 would be able to handle that easily, it would just be a matter of writing a simple program to blast to the PIC and constructing the circuit to drive the LED's.

What I would love to know is specifics on how Dereelight control the output of the LED in the DBS? What frequency the light is driven at would be most helpful... I think its in around 500Hz but am not sure about that... also what controller is used to get the PWM effect... is it a small microcontroller like a PIC or is it something simpler like a timer chip? I'm not sure of the extent all of your knowledge is with electronics but I do know that some of you guys design and even build your own flashlights with complex controllers, so I thought if I posted this here that someone may be able to help out a little.

So in summary:

I want to design a PWM controller for several sets of 4 LED's (4 per fan) which will run at the same freq as the DBS does in low mode so that I can alter the "perceived" speed of the fan blades to achieve the effect of the blades slowing almost to a stop whilst the PC is running, when in actual fact the fans are still moving air through the case.

Any help at all will be very much appreciated guys and girls, thanks for taking the time to read my post!

Matt

 

[Matt7337]

Just googled and found this. Wonder If I PM him will he give me a circuit schematic?

By his calculation: Frequency for stationary blades = (rpm/60)* Number of fan blades.

In my case that's: (1650rpm/60) x 7 blades = 192.5 Hz

The rpm value that the blades appear to stop in my case is 1650, using an Akasa PC fan controller professional model which has an LCD output for rpm values. It's a 120mm Sharkoon silent eagle 2000 fan, max speed 2000 rpm, min value on the Akasa fan controller (IIRC it varies voltage between 5V and 12V) is ~1200 rpm

 

[rmteo]

Google "stroboscope".
http://en.wikipedia.org/wiki/Stroboscope

A stroboscope, also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects. Machine parts and vibrating strings are common examples.
In its simplest form, a rotating disc with evenly-spaced holes is placed in the line of sight between the observer and the moving object. The rotational speed of the disc is adjusted so that it becomes synchronised with the movement of the observed system, which seems to slow and stop. The illusion is caused by temporal aliasing, commonly known as the "stroboscopic effect".
In electronic versions, the perforated disc is replaced by a lamp capable of emitting brief and rapid flashes of light. The frequency of the flash is adjusted so that it is a equal to, or a unit fraction below or above the object's cyclic speed, at which point the object is seen to be either stationary or moving backward or forward, depending on the flash frequency.

 

[Matt7337]

Thank you so much! I couldnt remember the name of the "Stroboscopic effect".

 

[VidPro]

a cheap way if you only want to do the pulsing at variable rates without programming or bugs, just whip out a 555 timer circuit
something like the tone generator at the top there, just put LED in instead of speaker
http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm

then use a 10turn pot to control the speed.

there are lots of easy simple curcits on the web for a 555, and if i can do it (ok it take me a while) anyone can. all it needs is a bit of power from the 5v line
use a mosfet to run larger ammounts of leds.

if you want readout, or perfect crystal controlled speed, then of course the programming will be needed. and what you would learn by using microcontroller chips would be much more valuable and usefull in a long run. why you could be doing your own displays in the cases.

something like the simple 555 you could have a few small leds running off the minor output of the thing in a few days tops, and see it working and then add a part or two to get drive current.

they say it isnt so precise, but you can control it with a 10 turn pot to very tight levels. and readjust as the fans age or change , or right after the first person sticks thier finger in one they thought was stopped

 

[KowShak]

The fans in my PC are all thermally controlled, their speeds vary as the PC heats up and cools down, so you'd need an "active" solution to keep the strobe synchronised with the fan.

Computer fans often have a fan rpm sense wire... a PIC could read the signal off that and use it to synchronise the strobe with the fan speed.

 

[VidPro]

mine are thermally controlled and variable too, and they are all at different rates depending on the need of each thing at the time, and size diferances too.

i would wonder how anyone could pull off a full sync. theatre lighting in the computer give each fan its own spot , mabey a backlight

 

[Matt7337]

Yes, I am actually using an "Mcubed T-Balancer" board to control the speed of the fans in the 2009 range of air cooled PCs. they allow either manual (active), automatic or preset control of the fan speeds to a high degree of accuracy through software only rather than varying voltages manually using a potentiometer based controller. I have used the T-Bal boards in pretty much all liquid cooled PC builds in the past, and have been able to control the rpm of both radiator mounted fans and liquid circulation pumps to within a few rpms, either thermally controlled or manually controlled operation is possible as it's a very versatile board powered by a microcontroller. I can control several different liquid loops depending on what is being cooled (CPU, GPU, Chipset etc) and each control system stays independant of the other.

I found several PIC solutions to the strobe effect, as well as the standard NE555 circuit schematic, just need to implement and test one or two of them and I should be on to a winner here

i would wonder how anyone could pull off a full sync. theatre lighting in the computer give each fan its own spot , mabey a backlight

I plan on buying clear 120mm LED case fans, removing the existing 5mm LED's and replacing them with my own strobing LED's. Two fans will be mounted at the front of the case behind a large mesh bezel, and another two exhaust fans at the rear of the case (case side panel is windowed). For the CPU cooler and GPU heatsink fan, I will just let the controller run them at whatever rpm they need to keep the temps in check.

 

[VidPro]

well that is just completly against your great build quality
everyone knows you cant get a Duel ball bearing high quality fan in a clear, they are art not science

you realise you have already obligated yourself to having to show us pictures .

 

[Matt7337]

You can actually, I have been using Sharkoons Silent eagle case fans a lot in recent years, and compared to the last brand of fan that I used (SilentX) they have about 300% more reliability. Sharkoons are available in Clear LED versions and feature exactly the same bearing as the "golf ball" style white silent eagle models. SilentX fans used to burn out after ~12 months use (At the time I stopped using them I did some extensive testing and found their weak spot to be the fluid bearing thats used) but Sharkoon fans just do not give out. I have systems with customers which were built 2 years ago or more with sharkoon style fans and they are as effective and quiet now as they were when they were built.

Another brand that are excellent for both build quality and reliability are Enermax, namely the cluster series. I have only started using them recently myself, but started on the advice of another system builder that I know personally. I wouldnt use them if I wasnt sure they were good quality, as obviously thats paramount in anything I build.

What would you like to see pictures of? I will of course post some for you if you want

 

[VidPro]

Yes, i would want to see pictures, especially after you get the leds synced up.