LED toy/night light project - advice/thoughts..

[chptunes]

If you were planning to build a simple LED circuit, to be used as a toy/night light.. in a 1590A box.. with a Momentary Power Switch..

..and you wanted a lot of brightness...

Would your circuit look anything like this?  What would you change?  Why?



-Corey

[alparent]

Is this for you? 

What is the goal of this build? Special education? just for fun?
Might help us help you?

[chptunes]

Is this for you? 

What is the goal of this build? Special education? just for fun?
Might help us help you?

This will be a birthday gift for my 5 year old.  He loves daddy's "projects".  He's always asking my wife if him and me can have some project time.. haha.

Anyway, beings that I'm just a couple of years into my DIY hobbying/hacking skills.. I wanted to see if there's something that you guys would do differently.. tips and thoughts, ya know.

[~arph]

Does the light need to stay on for a while after the switch is pressed?

[chptunes]

Does the light need to stay on for a while after the switch is pressed?

Nah, I think I want momentary actuation.. so it doesn't get left 'On' for several days and drain the battery. .. ..unless you have a simple way to set up a timed turn-off.

I already have one of these super-slick-arcade style switches:    http://www.mouser.com/Search/ProductDetail.aspx?R=LP0115CCKW01Fvirtualkey63300000virtualkey633-LP0115CCKW01F

[~arph]

Cool, then you can even leave out the 10uF cap.

[chptunes]

Cool, then you can even leave out the 10uF cap.

Well, I thought that By-Pass Cap would help the battery drain more efficiently.  Based on this quote from Mr. RG:

Filtering caps lower the apparent high frequency impedance of the power supply to the circuit. This matters to some circuits more than others. A good, low impedance power supply is nearly never a bad thing.

Batteries start out with a low internal impedance, but this gets higher as the battery is used. The filtering cap keeps the high frequency impedance that the circuit sees low even with the battery getting higher.

Maybe my night light project doesn't apply.?..

[armdnrdy]

Where are the input and output jacks?

It also needs a volume control!

You should use a stomp switch as well! How is he going to turn on the light while playing guitar? 

[Gurner]

Would your circuit look anything like this?  What would you change?  Why?

At 9V (as shown in your circuit), I'd use two LEDs in series because in your circuit you're dissipating most of the circuit's power across a resistor (grossly inefficient)...far better to dissipate the voltage across an extra LED (which will yield some 'win' in the way of extra light  vs. the resistor's purely heat 'loss')

For white leds (you never mentioned colour), two white LEDs in series amounts to about 6.6V ...therefore you've only got to 'lose' 2.4V across the series current limiting resistor (vs. 5.7V the way you've got a single LED in your circuit configured). Assuming a high brightness LED running at about 25mA, then the resistor should be calculated as 2.4/0.025, which is about 100R.

The 'filtering cap' wouldn't do much in your implementation .....for a start, there's no AC involved anywhere in that circuit - & you can't filter pure DC! (0Hz)

[chptunes]

At 9V (as shown in your circuit), I'd use two LEDs in series because in your circuit you're dissipating most of the circuit's power expended across a resistor (grossly inefficient)...far better to dissipate the voltage across an extra LED (which will give off light 'win'  vs. the resistor's heat 'loss')

For white leds (you never mentioned colour), two LEDs in series amounts to about 6,6V ...therefore you've only got to 'lose' 2.4V across the series current limiting resistor (vs. 5.7V the way you've got a single LED in your circuit configured). Assuming a high brightness LED running at about 25mA, then the resistor should 2.4/0.025 which is about 100R.

Thanks Gurner.  So, two LEDs in series with a smaller Current Limiting Resistor is more efficient and brighter.

Is this the right idea.. a 220R resistor should drop the current to about 10mA or so.

[Gurner]

Thanks Gurner.  So, two LEDs in series with a smaller Current Limiting Resistor is more efficient and brighter.

Well it's more efficient in that power expended is being wasted as (mainly) light power vs. heat power across the resistor as per your original schem. It'll also be brighter (due to two LEDs giving off more light than 1!)

Is this the right idea.. a 220R resistor should drop the current to about 10mA or so.

Yes, that's the idea... but a lot depends on LED colour, for example if you were using red leds (which I guess you're not for a night light - unless you live in Amsterdam), then you could use three LEDs in series (as they have a fwd voltage of about 2V). You can lose the cap, cos it's bringing zilch to the party.

[alparent]

Why not put a couple of different colored LEDs turned on by a couple of momentary switches?

As for your kid wanting to build with you...............it's the best feeling in the world.

I have a 9 year old and we have already built half a dozen projects togheter. Not effects but simple projects with ready made PCBs from RadioShack. We built a flashing heart for my wife for St-Valantine.
He his now soldering like a pro, reads resistor codes, check for his caps polarity.
He now want to build bigger thing! Mark Hammer sent me links to a site called Music From Outter Space and we already have 3 projects lined up. (I need to etch him double sided boards for these projects, I even put him the part layout silk on them!)

Investing time with our kids is the best thing for them.

He even started sitting dowm with the LapSteel guitar I built and testing out the different effects I've built. Rebote 2.5 is his fav.

Enjoy your kids! 

[Jdansti]

Red lights are actually pretty good night lights because they don't mess up your night vision.  If you use a white light at night, you have to give your eyes time to readjust when you turn it off. I've got a little red LED flashlight that's used by amateur astronomers to read charts while they're out at night with their telescopes. Works great for getting from the bed to the bathroom while avoiding bruised shins.

[deadastronaut]

@corey:

pfft!....nevermind all that lark ......build a ''joule thief'' circuit,  you can run 'lots' of leds off a 1.5v AA battery...even a dead one.

very cool....use up those dead batteries man!.....i even lit up leds and a string of xmas light leds too....lasts an amazingly long time.....





here's mine..
http://www.youtube.com/watch?v=kPCBwD7l9u0&list=UUGP0eO8ADt0H9FY5UcHTf8A&index=12

for the video lights, i wound (bifilar) 2 wires around a small ferrite ring, and just added the power switch.

like i say ive had lots of leds running off it, ...get the breadboard out...2 minutes ya done....and your boy will be very happy with daddy too.

i'm making a 20 led version for emergency/camping light...but i'll be using a small solar panel to recharge the 1.5v during the day too...

note to self:  try inductors!...

[petey twofinger]

prolly  a terrible idea but :

http://www.talkingelectronics.com/projects/5-Projects/images/LED-Flasher-with-TOUCH-pad.gif

maybe sub in a pot for that touch plate ... or go with a different schematic .

i did this and uses a dual gang pot for a pulse wah , the second led is an indicator , i use it as a sepcail fx , in a noise intro too  . i would say if he really lives it , maybe he could graduate to a cds theramin , with a headphone jack of course ....

[Gus]

Have you done a web search for     "high Brightness LED eye damage"  ?

[tca]

You could build a presence detector, just touching the box will light the led, no need for a press button .



Cheers.

[chptunes]

Thanks for the continued input folks.  I will consider your thoughts for my project.. I'm probably gonna keep this one basic and simple.  [But, I do have five kids.. so...]

Have you done a web search for     "high Brightness LED eye damage"  ?

Gus, I am sensitive to this topic.  After I have the enclosure openings drilled and the components in place, I will be testing different CLR/LED combinations to achieve the right brightness.

I think the design direction I'm headed for is ..a "night sky" night light.  Several small'ish holes drilled into a 1590A with between 1 and 3 LEDs glowing inside.  Direct point-of-vision will not be a safety concern, but a "night sky" effect could be enjoyed in a darkened room.

.. ...

-Corey

[deadastronaut]

^ be cool with a glowing perspex base plate too...

[rocinante]

I'm sure you've come across this, but if not-

http://led.linear1.org/led.wiz

A led array wizard. Was helpful to me when designing an led bike light!