LED Strobe Light Bar (how to strobe)

[runslikealpaca]

Hello all!

I am building an LED blacklight bar (approximately 48 20mA LED's, powered by a DC transformer that I found that is 9V with a max output of 800 mA).

So far, I have the schematic for having it just turn on and off, but I would like to have a setting where I can also make it strobe (all LED's on and all off). Does anyone have any advice for how to make all of the LED's turn on and off at an adjustable rate?

Preferably, just using hardware that I can find at RadioShack (Logic gates? because I don't know how to program small chips)

Thanks a lot!

 

[Sceadwian]

A simple 555 astable will work just fine. Look it up on google, or here in the forusm there are a multitude of examples. However 48LED's at 20ma's each is a lot of LED's so you'll need to make sure you can drive them all.

 

[runslikealpaca]

from what i can gather, i can power 1 or 2 leds directly off the chip. how can i use the signal generated by the chip to power all of the leds that i need to power?

 

[Sceadwian]

Easiest way is to use the 555 to drive the gate of a power mosfet that can handle the voltage and current going to your LED bank. You feed the 555 output into the Gate, the source gets grounded, and the drain is connected to the negative side of the LED array. Power mosfets that can handle that much current are pretty cheap.
Here's a website to show you how to build your LED array itself.
**broken link removed**

 

[runslikealpaca]

I found that website yesterday and used it to check the array I calculated (which was fine) my problem is I only have taken one electrical engineering class (intro) because I'm a mechanical engineering student, so we didn't really get into any of this stuff. I am a real novice, but had an idea the other day to build something like this. If there is any sort of schematic out there for how to use the power MOSFET that would be great. I can find how it works and such, but not how it would work in the circuit I'm building.

Sorry again to be a pain, I'm a rookie.

 

[Sceadwian]

A mosfet is just a type of transistor.
MOSFET - Wikipedia, the free encyclopedia
Basically you apply a voltage to the GATE relative to the source (which is why the source is commonly grounded) and it will allow Drain current to flow between the drain and source connections. You would drive the gate directly from the 555 timer which can only handle a small current, mosfets require VERY little gate current so much so it's not usually mentioned. So the 555 turns the FET on and off which turns your LED array on and off. A mosfet capable of 3 amps is available cheaply at radioshack.

 

[Boncuk]

Hi,

although Sceadwian has given you a lot of advise I guess you're still pretty helpless.

Here is a circuit which will drive your 48 LEDs at a total current of 288mA. The BUZ10 is a bit overkill (it can handle up to 20A), but it is cheap.

Additionally it won't require a heat sink for that small current.

Have fun.

Boncuk

 

[runslikealpaca]

thanks a lot, im gonna work on it

ill let you all know how it turns out

 

[Sceadwian]

I really gotta learn how to write good schematics =P The schematic Boncuk posted is exactly what I had in mind.

 

[runslikealpaca]

couple of small questions... sorry again fellas, youve been a great help, i just wanna make sure im doing it all right.

1. at the upper left of the shematic (when rotated to the right) the power supply is hooked up to the to an element called SV1.... what is that?

2. C1 and C4 have a "/16" and a plus over that, what does that mean? are those just polar caps?

3. R1 has a 6 after "5K" so it reads "5K6" What does that mean?

4. and finally, when using the LEDs in series, did you assume they were 2.4V leds or 3.6?

Thanks again,

I just wanna make sure I'm doing it right.

When im done, ill post links to pictures up here!

 

[jrz126]

1. That is just a 2 pin connector.
2. /16 is the voltage rating of the capacitor. and they are polar caps.
3. Thats just a different way of writing 5.6K. The decimal can be overlooked, and it might be misinterpreted as 56K. using 5K6 eliminates that possibility.
4. Looks like a Vf value of 2.4V was used. (See the * note.) What is the forward voltage of your LEDs? If it is 3.6V, then you can only run 2 in series and use a 90 ohm series resistor.

 

[runslikealpaca]

thanks a lot!