BASIC LED project - help/advice required

[higgface]

Hi there,
I’m working on something electronics based (very basic) at home and i’m a bit stuck because i know NOTHING about electronics. It's pretty much a nightlight for my daughter.

Basically I’m wanting to create a dark activated LED circuit - 12 LEDs in a grid with a light sensor and powered by a battery of some description.
The LEDs don’t need to be mega bright but the whole thing needs to be cheap as I’d be after making quite a few of them.

Moving forward - depending on how complicated it makes it - i may then need some sort of time-out after 20 mins to turn the LEDs off and save battery.
I also wondered if EL wire might be an option instead of the LEDs.

ANY help anyone can offer would be GREATLY appreciated!

 

[123jack]

1. That amount of LED's - make sure you get a bulk buy discount or register as a business customer somewhere
2. Battery - PP9 probably simplest with long life
3. Timer - 555 chip - perhaps the ultimate popular timer chip - circuits everywhere - just copy one
I've never used EL wire so can't comment on that - perhaps someone else could.
Or you could just buy a kit perhaps.

 

[higgface]

cool, thanks for your help.
I was looking for something reeeeeal simple like this:
https://www.evilmadscientist.com/2007/a-simple-and-cheap-dark-detecting-led-circuit/
but just with a few more LEDs and a timer... is it as simple as just adding more LEDs to that set up?
I can't seem to find any kits with what i need.

 

[123jack]

I like things that make me smile - that link made me smile - thank you. Very cool.
OK - yes you could do something like that - perhaps use discrete components for timing but 20 minutes may be a problem in terms of size/price - I'm not sure - depends on your local supply chain - Perhaps a kit with the basics you could modify ? ... its hard to say much more without knowing more but its a simple enough thing to do in many ways. If you're using lots of leds there are chips that may help but thats getting more complex than you appear to want. (resistor arrays / drivers and so forth)

 

[Audioguru]

The evilmadscientist circuit is EXTREMELY simple:
1) It uses the small size of the battery to limit the current in the LED.
2) It wastes a lot of current in the resistor whenever there is light.
3) Its tiny battery does not last long.

A 9V battery also will not last long powering 2 or 3 LEDs in series because it has six tiny AAAA cells inside.

You need a circuit that does not waste battery power when there is light and a battery big enough to power as many LEDs as you want for as long as you want.
An ordinary 555 timer wastes battery power all the time but a Cmos 555 timer wastes no power and can drive a transistor that can turn off a circuit after a timeout.

 

[123jack]

Audioguru
I dont dissagree - but I think you may be missing the point about evilmadscientist

 

[Audioguru]

Audioguru
I dont dissagree - but I think you may be missing the point about evilmadscientist

It is CHEEP! (cluck, cluck, cluck)
And it is simple.
But its tiny battery might not last longer than one night.

What is a throwie used for anyway?

 

[123jack]

..........Fun ?

 

[kam1787]

there are dozens of night-light 'build's here https://www.instructables.com/howto/night+light/

maybe one will be suitable

or https://www.circuitstoday.com/battery-operated-mini-night-lamp

or https://www.earth.org.uk/LED-homebrew-nightlight.html

not sure why you want so many LEDs - just one will do for a night light - I have some motion sensitive night lights and they are fine even though they have only one LED
You have 2 basic choices with wiring up LEDs; in series [daisy-chain], or parallel. Series requires a higher voltage [more batteries or a dc boost circuit]but consumes less power. Parallel needs lower voltage but consumes more power[more batteries].