LED Cyr wheel: More LED Notes

Circus/Cyr Wheel

Teensy/Hardware control

LEDs! I got my Teensy 3.1 board and started playing with the digital LED strips I got. I was having a heck of a time getting any sample code to work. I finally cut off the first LED and soldered the leads to the second one; then things started to work! I must have killed it accidentally; probably with reverse voltage, or other thing. As noted in Notes on v2 WS2812B LEDs would be better to use, as they have reverse protection built in.

What library to use?

I am looking at using the AdaFruit NeoPixel library, or the teensy OctoWS2811 library. I did a rainbow pattern with each. The octo library is GOBS faster, but occasionally flickers for some reason. The adafruit one is slower, but seems more consistent. I’ll probably abstract how I use each so I could switch back and forth with a #define. The website for the Octo has great info on the LEDs though.


I need a 5v power supply to test the LEDs. So, I need to figure out how much power they draw. The 59 LED strip I have draws 0.73amps at 5v, or about 0.01237amp per LED, or 12.4ma. I am looking at roughly 6m of LEds, 60LEDs per m, or: 360 LEDs per side, 720 total. I read on the Octo site that they can draw about 3 amps per 60 LED strip, so I’d be drawing up to 36 amps! I measured again at full white for my 59 LEDs, and got .87amps at most (870mA, or 14.8mA per LED)

spark fun says 60ma per LED. That would be: 60ma*720LEDs/1000=43.2amps. Yikes. Let’s not run them at full white! With a 2000mah Lipo battery that can do 15-20c, it could put out the 30-40amps required, but it would run for, oh, 4 minutes (2ah/30amps = .0667 hours = 4.00 mins).

Pololu says 4.7amps for 2meters of 60LED per meter. So, they calculate 28amps most for my 12meters total.

But my calculation on full white says: 14.8mA/LED*720LED = 10.6A. I think I’ll plan for about 15amps max..and uh, see how it goes. I won’t be running full white continuously.

The problem is for my testing I don’t have any way of providing any more than 2amps at 5v (a “wall wart” power supply that I have, or making my own ~1amp DC power converter circuit on a breadboard, which overheats). So, I have to order a better power supply, just for testing (I could use LiPO batteries..but I also don’t have any!). So, I ordered a 40amp (just in case!) 5v power supply from ebay for $30, which will come in handy in the future for other electronic projects.

I’m planning on using a 2cell Lipo battery for the power. I’m thinking of using two ~1.2 to 1.4ah batteries, since the runs are long (one for each half of the wheel). The LiPo battery will be 7.2v, too high for the LEDs. I need 5v. I ordered a small step-down voltage regulator from Pololu capable of doing 7amp continuous, and 15amp max. That should meet my design requirements (unless the stupid wheel really pulls more than 20 amps). I bought two…one for each battery, which might reduce the load in half. I might use one, or two; I’ll experiment on a breadboard first and measure actual power consumption. I also ordered some thermal adhesive from amazon (free shipping with Prime..I signed up this month since I’m buying a ton of stuff, and will cancel when the trial is over). I can use this to make the regulator have a large heatsink (the wheel!) to handle closer to the 15amp limit. Or, so I hope, and that’s only if I need to.

How long will the 1.4ah 7.2v battery last? It has: 1.4*7.2: 10.08watt/hours in it. The regulator is close to 95% efficient, so It’ll pass through 9.576watt/hours. At full white, 10.6amp*5v=53watts, so, I’m looking at only a 10 minute capability at full white. One color at a time will take 1/3 the power, so I could easily get 30 minutes with most patterns. Two batteries in parallel seem to be a must to double the amp-hours. That would give me 20 minutes of full white, and an hour run time “in general”. I just have to find some batteries that will fit in the wheel!

Need more LEDs

I realize now that I need more LEDs. I want two strips on each side. I also think I’m going to get “bare” LEDs and cover them in epoxy. So, I need to order some more. I want them to all be from the same batch..just in case there is some discrepancy. I need ~6m per wheel side, so 12m total. They are sold (usually) in 5m rolls, so I need 15m, which gives me some spares for “mess ups” (In addition to the 6m I already have, geez!)

WS2811/WS2812/WS2812B LED Sources. 60 LEDs per meter, and I need 12 meters min.

* AdaFruit NeoPixelWaterproof (not bare, not desired), not “B” (as far as I can tell). $23.95/meter. – $287.4 for 12 meters.

* SparkFun (where I already bought some). WS2812, but not “b” (I don’t think). $20/meter (roughly), bare. Come in 5m reels, but also sold by the meter. $240 for 12 meters.

* Pololu – WS2812B (the only one I know for sure has the B) – waterproof, $22.95/m (when ordering 10+): $276 for 12m.

* AliExpress – Looking into this option, as I might be able to get what I want for much cheaper.

http://www.aliexpress.com/item/Free-shipping-dc-5v-4m-240-leds-60-pixel-m-5050-smd-rgb-ws2812b-ws2811-led/1519096378.html – 4m/lot, 3lots: $140 (save $100!)

…and many others…

EDIT: I bought these from Ali Express.

Charger/power supply

I ran across this charger: Thunder-AC6-Charger-Power – http://www.hobbypartz.com/thac6smbachw.html– at $44. I bought the Turnigy Accucell 6, but, it didn’t include a 120v power brick, so I had to buy one:

1x #ACC6/18066 Turnigy Accucel-6 50W 6A Balancer/Charger w/ accessories (USA Warehouse) = $24.07

1x #HK15-5/34106 HobbyKing Power Supply 100~240v 5A (USA Warehouse) = $9.74

So, total about $34…but the Thunder one looks $10 better..so if I were to get another one I might go for that one. I also had to cut off the leads and put other ones on to match the AirSoft nano tech battery I bought (which I wasn’t happy about..but how well). Actually..my charger might have already died…geez.

I’m using a 3s 1.2ah lip cell (about 11.1v nominal) to test out in my original wheel first. Previously, I had 8-AA Nimh cells at 1400mah (1.4ah); slightly lower voltage (8*1.2v=9.6v), but they were working fine with the regular LEDs

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Turnigy Accucell 6 Charger: do not buy!

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