It may be simple, but it's something I'm not sure on - and I don't fancy wrecking my laptop!
I've got some Neopixel-esque LEDs on a string, made a couple of successful circuits and have also used a 1n4001 diode to drop the voltage of 4xAA to something the arduino nano can cope with.
The LED string tolerates 5-7v, according to the seller.
I'd like to be able to reprogram the nanos once they are in place, rather than having to use bulky headers that let me pull it out for reprogramming, because obviously anything more than a handul of LEDs is too much for my computer's USB port.
The circuit I've made is circuit A in the image. That also has the limitation of stopping the strip drawing more than an amp (diode rating). So I thought of circuit B, but I have a couple of questions:
Will circuit B stop the USB connection from powering the lights (thus protecting the USB port)?
Where would you put the "big" capacitor in that circuit? I think between diode and battery - is that correct?
Huge thanks for any help you can give this utter n00b.
The big cap... the Adafruit Neopixel guide (and I can't tell the difference between these and proper Adafruit ones) suggests that the string needs it for protection (though I've done several handful-of-lights circuits that didn't have it and so far still work).
Ah, okay. It's not for protection (at least not again damage) but for inrush currents. And because it's for the leds it's of little use on the Arduino side of the diode. So, indeed place it over the battery.
Ow, and by the way. Although you don't have a diode limiting the max current you can draw anymore, AA's are not very good at supplying large currents (and will be flat pretty quick). so if you're planning on driving loads of leds I would switch to a different battery.
Wokstation:
The circuit I've made is circuit A in the image. That also has the limitation of stopping the strip drawing more than an amp (diode rating).
No it absolutely will not. It is a diode, not a fuse.
When a diode has a 1 amp current limit, it doesn't mean that the diode will not let more than 1 amp flow through it, it means that putting more than 1 amp through the diode might break it.
Yeah, you can read that two ways. At first I read it like that but the second time I read it like "it stops me from connecting strips that draw more then 1A". Gave the topic starter benefit of the doubt.
septillion:
Yeah, you can read that two ways. At first I read it like that but the second time I read it like "it stops me from connecting strips that draw more then 1A". Gave the topic starter benefit of the doubt.
That makes no sense either. The mere presence or absence of some internal piece of circuitry isn't going to do anything to prevent you from hooking whatever you want to it. No diode could stop me from jamming the output wires into a mains plug if i wanted to.
If the batteries can't handle more than an amp, the user is responsible for plugging in the right thing, the diode will not prevent it or even help the rest of the circuitry survive if that happens. There are ways to ruggedize an output against overcurrent, and a diode isn't one of them.
Jiggy-Ninja:
The mere presence or absence of some internal piece of circuitry isn't going to do anything to prevent you from hooking whatever you want to it.
Yes there is, although mentally, and it's called knowledge
Jiggy-Ninja:
No diode could stop me from jamming the output wires into a mains plug if i wanted to.
septillion:
Yes there is, although mentally, and it's called knowledge
I am in "stick-in-the-mud" mode right now. Cutesy little smileys will not distract me from the fact that this exchange started with the the false idea of the diode limiting current, and has come to you saying "you have to know what you plug in", which is exactly what I said in P2 of Reply #6. Where does the diode fit in there?
Jiggy-Ninja:
No it absolutely will not. It is a diode, not a fuse.
When a diode has a 1 amp current limit, it doesn't mean that the diode will not let more than 1 amp flow through it, it means that putting more than 1 amp through the diode might break it.
The diode has a rating of 1 amp, thereby limiting what I can do with the LED strip without breaking the diode. I didn't say it acted as a fuse, but was referring more to what can be done with the strip - hence the reference to the diode rating. Gramatically, it made perfect sense, but I can see why you might have been confused.
Wokstation:
The diode has a rating of 1 amp, thereby limiting what I can do with the LED strip without breaking the diode. I didn't say it acted as a fuse, but was referring more to what can be done with the strip - hence the reference to the diode rating. Gramatically, it made perfect sense, but I can see why you might have been confused.
Septillion understood, anyway. Thanks again!
As long as we're on the same page then. That's the unfortunate quirk of language.
Where would you put the "big" capacitor in that circuit? I think between diode and battery - is that correct?
It should be as close to the LED strips as is physically possible. That means within a centimeter or two of where the power goes off the board to the strip. the NeoPixels surely use PWM for brightness control, which means the current is switched on an off quite rapidly. The capacitor is so this pulsing current doesn't cause power in other parts of the system to have excessive ripple.
I'd suggest adding a poyswitch resettable fuse in series with the + bat connection to protect against overload or shorts. Note that the "must" trip value is usually twice their current rating and their response is a bit slow, but those things work great!
