I was looking at these led's, and was wondering if I cut them up into pieces of three LED's each, would I be able to power the three LED's to a decent brightness and an ATtiny85 with three of these AAA Batteries Hooked up in series? Would this provide enough Amps? With three LED's I'm thinking they will need about 20mA each which would be 60mAh. Am I correct on that? I couldn't find how much mAh these batteries are rated at, but could someone help me understand if this would work? If not, do you have any other suggestions on how to power an ATtiny and a 3 LED Strip cost efficiently and without taking up a lot of room (I want the project to be as small as possible). Also, if you know much about LED's would you suggest using any other type of LED like the WS2812's or WS2812B for a project like this? Thanks
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\$\begingroup\$ 3 × 20 mA = 60 mA, not 60 mAh. Unfortunately you have linked to an Amazon ad page rather than a datasheet so we have very flimsy data to go on, particularly the operating voltage range. "No datasheet? No sale!" is our standard warning. \$\endgroup\$– TransistorCommented May 29, 2020 at 18:00
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\$\begingroup\$ keep in mind that ws2811 drives groups of three leds instead of having individual control like ws2812. \$\endgroup\$– dandavisCommented May 29, 2020 at 19:44
2 Answers
The linked LEDs are designed for 12V not 5V. You would be better off with 5V smart leds. You can under drive the 5V ws2811 LEDs to about 3.7 volts.
Yes 3xAAA would be enough to power 3 of the 5V LEDs at a decent brightness. Preferably you want Alkaline not Heavy duty (aka zinc) batteries for a longer life. Alkaline AAA would have about 2000 mAh, so assuming full white 60 mA for 3 LEDs that's 180 mA so roughly 10 hours per battery set. That value is optimistic, but if you have different colors and brightness and off periods the run time will increase.
You could go smaller with lithium cells but make sure you get a protection circuit and a charging circuit. There are tiny lithium packs that are the size of match books. Those are typically 3.6v so you may need a step up voltage converter so that adds complexity and lowers the battery life. You would basically be making a usb power bank.
So your best bet is to go with a small usb power bank. I've had one that was the size of car key fob.
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\$\begingroup\$ Look closer. They apear to come in 12V and 5V versions. Not surprisingly, the descriptive text is wrong, and it's "Sold by <jackasses> and Fulfilled by Amazon", so it's off the Marketplace flea market. Like eBay but with the cost of Amazon Fulfillment built into it. \$\endgroup\$ Commented May 29, 2020 at 18:18
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\$\begingroup\$ yeah, amazon is a rip-off for this stuff, compared to ebay, which is a rip-off compared to ali express... \$\endgroup\$– dandavisCommented May 29, 2020 at 19:45
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\$\begingroup\$ The LEDs are NOT powered by 12V ...it says directly that they are a 5V configuration. Since the lower operating voltage range is 4.5V the LEDs are unlikely to work on 3xAAA batteries since the terminal voltage will be below 4.5V under any form of load. \$\endgroup\$ Commented May 29, 2020 at 21:25
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\$\begingroup\$ @jack
About this item Working voltage: DC12V, 60mA Waterproof IP68also you are wrong about the 5v ones not working at lower than 4.5v but whatever. \$\endgroup\$– PasserbyCommented May 29, 2020 at 22:31
Short answer....No, your schema is unlikely to work. The LEDs you link to come in two varieties.....5V and 12V. Clearly you are settled on the 5V version. Looking at the datasheet for the WS2811 gives you all the data you need.
The configuration of the individual LEDs is:
Referring to the datasheet again, the rated voltage on VDD for the WS2811 is 4.5V-5.5V.
Your 3xAAA batteries will only produce 4.5V when new, and under any load will be below the recommended voltage range. Operation is there questionable, although the ATTiny85 will obviously operate at voltages below 4.5V.
One potential solution is to use NiZn batteries which have a terminal voltage of 1.6V. 3xNiZn would give you 4.8V, which is within range. BUT, if you use a commercial charger for the NiZn it will charge them to 1.9V which is above your maximum rated voltage. I use a commercial charger for these batteries, but have a shunt regulator over the battery (TL431) to prevent the voltage rising above 1.8V. This works well, but means you don't ever 100% charge the battery.
The discharge for NiZn looks like this:
In summary:
- Your choice of 5V LED based on the WS2811 is fine
- You will run into brightness and color problems with 3xAAA
- You could use 3xAA NiZn to get around the problems providing you limit the terminal voltage under charge to 1.8V
