# What kind of switch and configuration do i need for LED's?

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#### purplelirpa

##### New Member
I have limited electronic experience, know the names of things, how to solder, but don't really know much about the logic involved w/electronics.

What I'm trying to build:
a board with 36 led's (red, green, yellow)
6 switches driving 6 same-color led's each
2 9v batteries to each switch
led's connected in series, 1 resistor (still have to do equation to find which one) for each group of 6 led's

What I want the led's to do:
be able to turn on, off, and toggle on/off, preferably at a moderate/slow pace

I want the ability to turn on and off each section of the grid or have 1 section flashing and another section off/etc. If I can accomplish this with a fancy, expensive switch that can toggle between pulsing on/off or staying on or staying off, I'd rather do that.
If this can't be accomplished, I will need a little more knowledge about how to design the circuit properly, anyone have any tips?

#### MikeMl

##### Well-Known Member
Are you familiar with a 555 timer ic chip?. Using one of these, it is simple to produce a free-running pulser whose pulse rate and on-time can be easily set. It runs fine on 9V.
It is capable of switching 200mA, so if you are using up to six strings of 20mA LEDs, that is only 120mA.

Are you familiar with a center-off single-pole double-throw miniature switch? If so, wiring that up to turn off the LED string, Turn-on the LED string steady, or connect the LED string to the 555 output pin is easy.

To light six LEDs in series, 9V is not enough. If you tie two 9V batteries in series, the current limiting resistor will be R=E/I=(18-6*Vf)/0.02, where Vf is the forward drop for one LED. Note that each color LED has a unique Vf; you will have to look it up for the specific LEDs you are using. It will be somewhere between 1.6 and 2.4V

#### audioguru

##### Well-Known Member
A 9V battery quickly drops to 7.2V. Two in series will quickly drop to 14.4V and six LEDs can be in series if their voltage is 2.2V or less.

If the LEDs operate at 25mA and all six groups are turned on then the 9V alkaline batteries will last for about 45 minutes.

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#### purplelirpa

##### New Member
Hmm..that will be an issue with the 9v power supplies. The original reason for choosing that battery was a size constraint. This will be a part of a costume, batteries will be between skin and cloth. Is there a better, more powerful option that is small enough to fit on the arm? original idea with the 9v's was to tape them to the arm, or if they were too hot, put something in between arm and batteries and tape.

#### MikeMl

##### Well-Known Member
Get some "ultra-bright" LEDs, and run them at 5mA. They are surprisingly bright even at 5mA.

#### purplelirpa

##### New Member
I'll have to read up on the 555 timer, I'm curious if there's a way to keep the 9v's, but extend the time past 45min. I'm not opposed to dimming them a little if necessary. Would changing the resistor be a good way to accomplish that?

#### unclejed613

##### Well-Known Member
if you know somebody who still regularly uses a Polaroid camera, collect their used film packs. there are very flat batteries (about 1/8" thick) in them that still have quite a bit of life in them. they are 6V batteries, and have a lot higher current capability and capacity than a 9V (they're just 6V instead of 9). 2 of them in series would give you 12V. i always thought they would make excellent batteries for LED projects.

#### audioguru

##### Well-Known Member
Most "ultra-bright" LEDs are just ordinary cheap ones focussed into a narrow beam. They are bright when pointing directly at you but can barely be seen in the dark when they are not pointing at you.
You need wide-angle LEDs and you need to operate them at a high enough current to be seen in daylight. A half-decent battery can not be taped to an arm.

#### Boncuk

##### New Member
Low current LEDs have a forward current of 2mA and the same radiation pattern as any ordinary 20mA-LED.

They can certainly be used to extend battery life time.

Check out at Kingbright.

Boncuk

#### audioguru

##### Well-Known Member
Low current LEDs have a forward current of 2mA and the same radiation pattern as any ordinary 20mA-LED.

They can certainly be used to extend battery life time.

Check out at Kingbright.

Boncuk
They have a luminous intensity and radiation pattern exactly the same as the ordinary Fairchild red LEDs that I have used for years.
At only 2mA their intensity is exactly the same: 20mcd, very dim.
At 20mA their intensity is exactly the same: 200mcd, bright.

#### unclejed613

##### Well-Known Member
real ultra-bright LEDs are usually in the large 10mm size. they have an intensity of 12000mcd at 20mA and can be easily seen in daylight. they can be found very inexpensive at www,newark.com

the manufacturer is ON Semiconductor.

#### audioguru

##### Well-Known Member
real ultra-bright LEDs are usually in the large 10mm size. they have an intensity of 12000mcd at 20mA and can be easily seen in daylight. they can be found very inexpensive at www,newark.com

the manufacturer is ON Semiconductor.
Newark does not list any ON Semi LEDs.
I found a 10mm Toshiba red LED with 15,000mcd brightness but its angle is only 4 degrees like a laser pointer. It costs \$2.65US.

#### purplelirpa

##### New Member
well, here's what I've been looking at:
Multivibrator - Wikipedia, the free encyclopedia
Using A 555 Timer Chip

video close to what I'm trying to make (only it doesn't seem to have a plain "on," just a blinking one).

some switches:
SPDT, CENTER-OFF, ROCKER SWITCH | AllElectronics.com
SPDT CENTER-OFF ROUND ROCKER SWITCH | AllElectronics.com

LEDs:
still looking for a good site with cheap ones, but basically just want a wider viewing angle that can tolerate less mA and V while still being visible. See question about potentiometer below.

some questions:
could I use a potentiometor (sp?) instead of a resistor so that I can adjust the mA and dim or brighten the leds or would that mess up the oscillation? It seems to me that the pulsing function would use less mA than the fixed on position would.

I'm having trouble picturing how the circuit layout is going to work differing between the "on" switches. Will this be called an astable or bistable circuit? I am having trouble understanding the schematics. This is probably because I don't yet understand the limiting factors of the multivibrators and how exactly it makes the blinking, off, and fixed on.

I'm still set on 9v (bought 12 of them when they went on sale for a dollar each at radioshack yesterday), so if I can make it work with 9v, I can adjust other things (I hope).

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