Hi all. I'm new here and a bit of noob when it comes to putting a circuit together. This should be pretty simple for the experts!

I've built a clock out of a laptop hard drive. I want to add some LED's but I have some issues I need help with:

1. The clock mechanism is powered by a single AA battery, is 1.5 volts enough to also power up to 12 red 3mm LED's?
2. I do have the option of using two AA batteries to power the LED's though, is 3 volts too many for the 3mm LED's?
3. I read somewhere that 3 volts would burn coloured LED's out sooner than if they were white. I also read that including a 3.3Ohm resistor would solve this problem. If I were to use 3 volts to power the LED's where would I position the 3.3Ohm resistor in the circuit?
4. I have a momentary switch, I'd like to be able to press it to light up the LED's for 10 seconds and then it automatically turn off again. How do I do this? What additional component do I need for this timer to function?

I'm positioning the LED's behind one of the hard disk platters (clock face), one for each hour (maybe, or just several). I'm mounting a momentary switch to the front so when I want to check the time in the dark I just press it and the LED's light up for 10 seconds and go off again, while the clock is still powered by the single AA battery. I've got the LED's, 3.3Ohm resistors, momentary switch, wires and heat shrink.

 

A single 1.5V battery will not reliably work am LED but 3V is good. You will need a resistor of between 150Ω and 330Ω (3.3Ω would give too much current through the LED). You need one of these resistors in series with each LED.

For timer a circuit like this will do the job:

Connect your LEDs and series resistors where R1 is shown.
Q1, Q2 2N2222A
R2 3k3Ω
R3 330Ω
R4 Zero - just link Q2 collector to Q1 base.
C1 4700uF for 10 seconds delay.

 

Wow, okay. When I said "noob" I really meant it. I don't understand any of that!

Typing those things into Amazon I see that:

Q1 and Q2 are: 2N2222 NPN TO-92 Plastic-Encapsulate Power Transistors 75V 600mA
R2 is a: 1/2W Watt 3.3L ohm 3K3 Carbon Film Resistor 0.5W
R3 is a: 330R Carbon Film 1/4w 0.25w 5% Tolerance 330 Ohm resistor
R4 is a: actually not sure what this is, nothing?
C1 is a: 4700uF 10v Radial Electrolytic Capacitor

I don't know what the other symbols are on the diagram, what is the thing underneath it all? Is +v and 0v the positive and negative from the batteries? When you say connect LED's and resistors to R1 - how?

Told you I was a noob!

 

When you say connect LED's and resistors to R1 - how?

This diagram shows four LEDs - you just add more as required. The brown things are the LED resistors. The red wire connects to positive battery connection. The black wire connects to Q1 collector and you don't need R1 (The LEDs and their resistors do that job).
Note that the LEDs have to be connected the right way round.

The lead marked positive connects to the resistor in the above diagram and the negative lead connects to Q1 collector.

what is the thing underneath it all?

If you mean the square squiggle you can ignore that. That is the representation of the trigger pulse but you are using the momentary switch to generate that.

Is +v and 0v the positive and negative from the batteries?

Yep.

 

This diagram shows the transistor connections:

 

Thanks AlbertHall, that's a lot clearer now! I'll be able to make a start just as soon as Amazon deliver by LED's!

The items I listed above that I found on Amazon, are those the right things I need? Not too sure on the 4700uF 10v Radial Electrolytic Capacitor, there are several 4700uF capacitors of various voltages. I think the one I found (10v) is too large...?

I might need some more help when I start soldering this together!

 

The capacitor can any voltage rating greater than 3V, you might find a 6.3V one. The lower the voltage rating the smaller it will be, but it will still be fairly big. You are right with the other things.

 

The capacitor can any voltage rating greater than 3V, you might find a 6.3V one. The lower the voltage rating the smaller it will be, but it will still be fairly big. You are right with the other things.

Great, thanks. I hope I can squeeze all that in behind the clock, it's a laptop HDD so it's pretty small!

 

I don't understand any of that!

I think you will find it much benefitial if you approach the learning in a systematic way. picking up bits and pieces works from time to time but not as efficient / effective.

 

It is difficult to tell time with a single lit LED in the dark with out a frame of reference. Maybe dim yellow LED's
to mark other 11 hours, or maybe flash the hour number ?

 

It is difficult to tell time with a single lit LED in the dark with out a frame of reference. Maybe dim yellow LED's
to mark other 11 hours, or maybe flash the hour number ?

My initial intention was to have one red LED per hour arranged in a circle behind the disc platter - hopefully enough of the light would spill out onto the silver disc platter to view the hands. Unfortunately this is no longer an option as the space behind the disc platter isn't deep enough to accommodate the 3mm LED's and resistors.

I've had a look at LED strips, EL string with controller, various other types of lighting and I can't find anything suitable. The EL string would have been ideal as it would only just fit under the disc platter, an 8" strip in a circle just behind the platter around the edge with the wires for the controller passing through a hole behind. But the EL string doesn't look bright enough in videos I've seen.

So I'm stuck with this:

As a clock it looks and works fine but I wanted lights. Not sure what to do now.

 

How about this kind of LED: http://uk.farnell.com/standard-single-colour-leds-under-75ma/led-mounting/smd/pg/110144644
They are very thin.

 

How about this kind of LED: http://uk.farnell.com/standard-single-colour-leds-under-75ma/led-mounting/smd/pg/110144644
They are very thin.

Yeah they could work! They look like the ones in the moulded strips. How do you circuit these up? Do I need different resistors for these? Again though resistors won't fit underneath the disc platter, I have only about a depth of 2.3mm.

EDIT

What I need is a circle of these at 6cm circumference to go under the disc platter.

EDIT

Also I'm quite liking the idea now of having this clock powered by USB (for the lights). There are some pretty cool strip lights with remote to change colour and strobes etc. Unfortunately they're all too thick.

 

You could put them where you want and bring wires out to connect the resistors or there are SMD resistors too:
http://uk.farnell.com/webapp/wcs/st...tegoryId=700000005450&langId=44&storeId=10151

 

The SM LED's that I used for a " holiday hat " are 2.8 X 3.15 X 1.88 mm thick, just wrong color- white. 1/8 th.
W R 1.88 mm dia. Similar size LED probably in red also. Might use 2 LED's to mark 12 O'clock? Are you going to drill holes in disc over the hour LED's ?

 

The SM LED's that I used for a " holiday hat " are 2.8 X 3.15 X 1.88 mm thick, just wrong color- white. 1/8 th.
W R 1.88 mm dia. Similar size LED probably in red also. Might use 2 LED's to mark 12 O'clock? Are you going to drill holes in disc over the hour LED's ?

No, I was hoping enough light would bleed through the gap between the disc and the sides of the HDD. If I drill holes in the disc platter it'll ruin it.

 

I do not think that there will be much light bleed thru, could mount LED's beyond edge of disc.
Has anyone acid cleaned a disc to make it semi transparent?

 

I do not think that there will be much light bleed thru, could mount LED's beyond edge of disc.
Has anyone acid cleaned a disc to make it semi transparent?

That's what I wondered. It would be pretty cool to acid etch actual numbers on the metal disc. Not sure if that's possible or how.

EDIT

I'll buy some SMD lights in the mean time. I need to experiment with my options.

 

Hard Drive Disks are aluminum. They're not going to be transparent. Which crops up a new idea - maybe use an old CD or DVD. Those will shine light through them. And no need to drill anything. They'll likely be larger diameter than the HDD aluminum disks, so you might be losing some of the effect you're after.

 

Hard Drive Disks are aluminum. They're not going to be transparent. Which crops up a new idea - maybe use an old CD or DVD. Those will shine light through them. And no need to drill anything. They'll likely be larger diameter than the HDD aluminum disks, so you might be losing some of the effect you're after.

They can also be glass/ceramic which you may get some light through. Try it and see.