NeoPixel-UserGuide-Alimenter

Alimenter des NéoPixels

Les NéoPixels sont habituellement décrits comme des "périphériques 5 Volts” mais la réalité est un peu plus nuancée que cela.

Certains produits NéoPixels (pas tous) peuvent fonctionner avec une tension sensiblement plus élevée. Cela dépend des composants additionnels placés autour des puces NéoPixels, composants additionnels qui dépendent de l'espace disponible, le coût et de l'application. Référez vous à la page de description spécifique à chaque produit pour les recommandations sur les limites de tension acceptable pour chaque type. En cas de doute, optez pour 5 Volts.

Les tensions inférieures sont toujours acceptables avec la conséquence que les LEDs éclairerons moins. Il y a une limite en dessous de laquelle la LED ne s'allumera pas, ou commencera à produire une couleur incorrecte.

All the images here under are credited to AdaFruit Industrie - Crédit à AdaFruit Industrie pour toutes les images ci-dessous

	Avant de connecter un ruban NéoPixel sur N'IMPORTE QUELLE source d'alimentation, nous recommandons fortement d'ajouter une grosse capacité (1000 µF, 6.3V ou plus) entre les pôles + et –. Cela protège les NéoPixels des dommages que peuvent causer la pointe de courant initial.
	Nous recommandons des accu lithium-polymère pour de nombreux projets fringuables. Il délivrent 3.7 Volts — parfais pour alimenter directement des microcontrôleurs basse consommation tel que les Flora d'AdaFruit, cette tension est également suffisante pour faire fonctionner une courte section de NéoPixels.
	Trois piles alkaline (tel que des pile AA) peuvent être installées dans un boitier et produisent 4.5 Volts. Même si l'ensemble est nettement plus encombrant et plus lourd qu'un accu lithium-polymer, il a l'avantage d'être abordable financièrement et d'être immédiatement disponible.
	4 piles rechargeables NiMH (nickel-metal hydride) peuvent être utilisés dans un boitier à 4 piles pour fournir une tension de 4.8 Volts. Dans cette configuration à 4 piles, Assurez-vous qu'il s'agisse bien de pile NiMH! 4 piles alkaline (la version non-rechargeable) produiraient une tension totale de 6V — that’s too high for some NeoPixels, and definitely too much for the microcontroller!

Battery-operated LED project planning is discussed in greater detail in Piles et accus pour alimenter les LEDs et Rubans NéoPixels.

	For most non-portable “desktop” projects, a 5V DC switching power supply is ideal. This small 2 Amp supply is good for a a meter or so of NeoPixel strip. We’ll explain larger projects in a moment.
	Be extremely cautious with bench power supplies. Some — even reputable, well-regarded brands — can produce a large voltage spike when initially switched on, instantly destroying your NeoPixels! If you use a bench supply, do not connect NeoPixels directly. Turn on the power supply first, let the voltage stabilize, then connect the pixels (GND first).

Estimation de la puissance nécessaire

Each individual NeoPixel draws up to 60 milliamps at maximum brightness white (red + green + blue). In actual use though, it’s rare for all pixels to be turned on that way. When mixing colors and displaying animations, the current draw will be much less. It’s impossible to estimate a single number for all circumstances, but we’ve been using 1/3 this (20 mA per pixel) as a gross rule of thumb with no ill effects. But if you know for a fact that you need every pixel on at maximum brightness, use the full 60 mA figure.

To estimate power supply needs, multiply the number of pixels by 20, then divide the result by 1,000 for the “rule of thumb” power supply rating in Amps. Or use 60 (instead of 20) if you want to guarantee an absolute margin of safety for all situations. For example:

• 60 NeoPixels × 20 mA ÷ 1,000 = 1.2 Amps minimum
• 60 NeoPixels × 60 mA ÷ 1,000 = 3.6 Amps minimum

The choice of "overhead" in your power supply is up to you. Maximum safety and reliability are achieved with a more generously-sized power supply, and this is what we recommend. Most power supplies can briefly push a little extra current for short periods. Many contain a thermal fuse and will simply shut down if overworked. So they may technically work, but this is the electronics equivalent of abusing a rental car.

J'ai besoin de 3.6 Amp. Est-ce que cela ira avec un bloc de 10 Amp?

Question: I estimate I need a 3.6 Amp power supply. I have a 10 Amp supply on-hand. Will this cause my NeoPixels to explode? As long as the output is 5 Volts DC, you’re golden. The LEDs will only draw as much current (Amperes) as they need. So extra Amps are OK — in fact, it can be a good thing. The larger power supply will run cooler because it’s not being pushed to its limit.

Excessive voltage, however, will definitely kill your LEDs.

Extra Amps = good. Extra Volts = bad.

Piles et signification "Amp heure"?

Amp-hours are current over time. A 2,600 mAh (milliamp-hour) battery can be thought of as delivering 2.6 Amps continuously for one hour, or 1.3 Amps for 2 hours, and so forth. In reality, it’s not quite linear like that; most batteries have disproportionally shorter run times with a heavy load. Also, most batteries won’t take kindly to being discharged in an hour — this can even be dangerous! Select a battery sufficiently large that it will take at least a couple hours to run down. It’s both safer for you and better for the longevity of the battery.

Puis-je utiliser plusieurs alimentations?

Question: I need to power LOTS of NeoPixels and don’t have a power supply that large. Can I use several smaller ones?

Maybe. There are benefits to using a single supply, and large power supplies are discussed below. “Non-optimal” doesn’t necessarily mean “pessimal” though, and we wouldn’t discourage anyone from using what resources they have.

If you go this route, the key is to have all of the ground pins among the strips connected in common, but the +5V from each power supply should be connected only to one length of NeoPixels — those should not all be joined. Every power supply is a little different — not precisely 5 Volts — and this keeps some from back-feeding into others.

Bloc d'alimentation - les montres de puissance

MCHobby propose un bloc d'alimentation 5V continu pouvant fournir jusqu'à 10 Ampères. This is usually sufficient for a couple hundred NeoPixels or more. For really large installations, you’ll need to look elsewhere.

One possibility is to repurpose an ATX computer power supply. The nice beefy server types often provide up to 30 Amps. Some minor modifications are needed…Google around for “ATX power supply hack.”

Even larger (and scarier, and much more expensive) are laboratory power supplies with ratings into the hundreds of Amps. Sometimes this is what’s needed for architectural scale projects and large stage productions. And occasionally we get requests for help…

Please note that projects of this scale are potentially very dangerous, and the problems of power distribution are fundamentally different than hobby-scale projects. As much as we enjoy helping our customers in the forums, they are for product technical support and not full-on engineering services. If you’re developing a project of this scope, hire a professional electrician with experience in high-power, low-voltage systems such as photovoltaics or large RVs and boats. This is no charade.

Distribuer l'alimentation

The longer a wire is, the more resistance it has. The more resistance, the more voltage drops along its length. If voltage drops too far, the color of NeoPixels can be affected.

Consider a full 4 meter reel of NeoPixels. With 5V applied at one end of the strip, for those pixels closest to this end, power traverses only a few inches of copper. But at the far end of the strip, power traverses 8 meters of copper — 4 meters out on the +5V line, 4 meters back on the ground line. Those furthest pixels will be tinted brown due to the voltage drop (blue and green LEDs require higher voltage than red).

Crédit: AdaFruit Industries www.adafruit.com

Un truc de Pro: NeoPixels don’t care what end they receive power from. Though data moves in only one direction, electricity can go either way. You can connect power at the head, the tail, in the middle, or ideally distribute it to several points. Try to aim for about 1 meter lengths for the best color consistency. With larger NeoPixel setups, think of power distribution as branches of a tree rather than one continuous line.

Crédit: AdaFruit Industries www.adafruit.com

Distribution sur un projet Fringuable

Resistance is just as much a concern on tiny projects too!

For wearable electronics we like conductive thread…it’s flexible and withstands hand washing. Downside is that it doesn’t carry much current. Here several strands of conductive thread have been grouped to provide better capacity for the + and – conductors down a pair of suspenders.

Crédit: AdaFruit Industries www.adafruit.com

Piloter des NéoPixels 5V avec un microcontroleur 3.3v

Increasingly, microcontrollers are running at 3.3 Volts instead of 5 Volts.That’s great news for efficiency, but can present a communication problem with 5V NeoPixels. The 3.3V signal from the microcontroller may not be “loud” enough to register with the higher-voltage device. The manufacturer recommends a minimum signal voltage of 70% of the NeoPixel voltage.

There are two ways this can be addressed:

• Lower the voltage to the NeoPixels so it’s closer (or equal) to that of the microcontroller. This is why we recommend LiPo batteries for FLORA projects: 3.7V is enough to run a short length of pixels, and the microcontroller is comfortable at that voltage as well.
• Use a logic level shifter to step up the signal from the microcontroller to the first pixel.

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Source: NeoPixel UserGuide créé par Phillip Burgess pour AdaFruit Industries. Crédit AdaFruit Industries

Traduit par Meurisse D. pour MCHobby.be

Traduit avec l'autorisation d'AdaFruit Industries - Translated with the permission from Adafruit Industries - www.adafruit.com

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