/diy/ - Do It Yourself

>>373431
Voltage pulls, current gets pulled. You showed that you are ignorant of that in your posts.

>>373407
1.5/40=37mA

OPs maths is solid, the circuit will only draw 37mA per branch, which is a good amount for the LEDs. Do you have any idea what you're posting about?

You shouldn't try to run maximum rated current through an electrical component, particularly LEDs. You'll just cause them to burn out quicker. 80% of rated capacity is a good safety margin, which is what I think OP was aiming for.

>>372651
Best post ever.

OP I'm doing the same thing with infrared LEDs. I'm planning to mount them to a Coldplay CD I have lying around (because fuck Coldplay). Hopefully by using a hot needle I can poke holes through and solder it really carefully.

I'm only using 20 LEDs, each is 1.5V and 60mA so I'm having branches of 5 with a resistor so they draw a total of about 100mA of current, batteries last ages at that kind of current draw (about 5 hours off a 9 volt).

>>370374
Put a reflector behind the LEDs and they direct light much better.

LED wattage is not what you should be looking at. LED brightness is measured in millicandella, if you're creating a desklamp even a single 26000mca 3.1V 30mA LED would be more than enough to fully illuminate a desk. An LED like that would only cost $1 or so. And you could wire up several of them with almost no power draw.

The LEDs I'm using for my spotlight are the infrared equivalent of 15000mca, meaning they are extremely bright. And with 100 of them in the array they should be more than bright enough to illuminate the small patch of yard I need to be able to see at night.

>>370309
The maths is solid, I suspect you haven't read this thread and come to an understanding of how basic electronics work. Reading this thread properly will correct your thinking, there is a lot of valuable information and explanation here.

Wait so I can't collect rainwater Michigan? Tell that to my 10gal filtration system.

>>369909
Assuming they aren't a dud, which they may well be. These aren't precision components.

>>369899
OP has given us the voltage drop, approximately 3.1V according to him.

>>369897
Except when one of them blows you have to rewire the whole thing. And with a 3v drop on each LED he can only really have three in a series at a time. Hence >>369885 this design.

>>369710
These are in parallel already. Having one to a branch seems like overkill, would make the wiring much uglier on a board and would waste all of my resistors.

This way, if 1 blows 5 more of them go out, but the other 100 stay on.

>>369883
This schematic should work. With 120ohm resistors you draw just over 24mA of current which is pretty much 80% of the capacity of your LEDs. You can add as many branches of LEDs as your power supply supports, as each of them draws 24mA you can add about 8 on a 250mA power supply.

>>369852
Never use LEDs without a resistor in front of them.

OP you can wire more of them in series. I'd suggest three to each parallel branch with an appropriate resistor in front of each branch. If you have two more LEDs you could fit them there. I'll come up with a diagram in a minute.

>>369564
iPad

>>368914
Just to double check, 5LEDs connected in series to a 9V battery with the equivalent of a 30ohm resistor in series with them will receive about 50mA of current. If the battery starts at 9.6V, this will potentially fry the LEDs because they will receive 70mA at that voltage.

So a 40ohm resistor would be good because at 9.6v it will deliver 52.5mA to the LEDs, at its lowest it will deliver 12.5mA and at 9V it will deliver 37.5, all of which are decent values for operating the LED.

>>368914
>>368917
Thanks, I've got it now.

Another noob question:

Lets say I have 6 LEDs wired in series with a 9v battery. The calculators tell me I should throw in a 1ohm resistor, obviously to account for variance but as the voltage over the resistor would theoretically be 0 doesn't the equation above mean there'd be no current drawn? (0V/1R=0A)

I'm assuming because the resistor is just there to cover me in the event the LEDs aren't precise, the current over this resistor doesn't matter much at all, but don't all components end up with the same current going through them?

>>368562
That's the point, hopefully intruders won't notice the system until I have their face saved on my hard drive.

I'm using 850nm IR LEDs which do give off a faintly visible pink glow, but it isn't bright enough to be immediately noticeable.

>>368555
Thanks, I couldn't work out why exactly I needed them but that makes a whole heap of sense.

My project:

I'm building a home security system to watch my yard at night. We've had some prowlers come into our yard at night (as evidenced by random boot prints, unidentifiable grimy hand prints on walls that none of us made, strange sounds, makeshift beds by our wood pile, etc). Rather than fork out $500 for a decent night-time security system, I thought I'd build my own.

I've already dismembered about 5 USB webcams and removed their IR filters. The best one is a 720p I got off a friend who thought it was broken for $5. It's quite sensitive to infrared light so it should be perfect. The other cameras could come in handy if I decide to mount multiple cameras. The camera is hooked up to a server running iSpy so it records whenever it detects motion at night.

It's passable in the dark, but I want to build an spotlight that can illuminate a reasonable portion of the yard to improve the motion detection capabilities and maybe improve the image quality enough to make out identifying features of an intruder. I've already been using a standard LED spotlight which is very small, not very powerful and very obvious, so to add a bit of secrecy to it I want to use infrared LEDs, but I'm trying to wire it on the cheap. You guys have been a huge help so far.

>>368542
*150ohm, not 160ohm

>>368521
So let me get this straight, if I put two 160ohm resistors in parallel across each series branch they effectively act as a 75ohm resistor.

Using those, each branch will draw exactly 40mA of current (A=V/R=3/75=0.04), so each LED will receive 40mA of current. And this will be fairly bright for the LED and is below capacity so they will last for ages.

I'm using 150ohm resistors because I got given 100 of them so it's convenient they work out roughly right (assuming my math is correct).

Thanks for all your help guys, now I need to buy way more LEDs because it seems my power supply can handle a massive number of them. Learned a lot here today.

>>368521
Thanks, learning loads over here.

>>368442
Just on my math, using the second diagram I posted above, wouldn't a 75ohm resistor give me 60mA of current across each branch of the parallel circuit, meaning that each LED gets their maximum rated current?

I think I'll go for 150ohm resistors to reduce the current a bit to add longevity to each LED.

If I wire two 150ohm resistors in parallel, do they act as a 75ohm resistor or am I horribly mistaken?

>>368053
So something like this? But wouldn't the reduced current reduce the amount of light each LED emits? I'm aiming for maximum brightness.