LED Poi w/ 9DOF Questions/Guidance

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I have the schematic designed and the board layout proved to be pretty tight with 2 layers (not that this has stopped me before!) so I put it aside. Now that I am regularly working in four layers I think I'll return and get this board made and tested. Sorry for the delay, I've been distracted by many other things. I might have something on Tindie by the end of August (I'm going camping for ten days).
 
When I get back from camping I'll start a new thread covering a few new items for the Teensy 3.1 I have been working on.
 
onehorse said:
I was going to take some of my valuable time and offer free advice but if you come "here expecting sound advice from people who know what they're talking about" without the least courtesy and grace I think I'll spend my time elsewhere...
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I think he's entitled to a full refund of the consultation money he paid you for your help. Heck, send him double his money back.
 
Yeah, I should also start a new thread, as the 800 LED POV staff is now spinnable and people may be interested in that. I've yet to get a good photo though, due it being too bright.

I'm also interested to hear more about the higher current lithium charging. I'm using 6S packs and 5 Volt converters, but it seems like APA102 strips will happily run off the Voltage from a single lithium cell or a heap of cells in parallel. That means I can do without the converters and get higher peak currents for more brightness. However, the pack for the staff is 12 14500 cells, so 30 Wh. Putting all of those in parallel and charging at USB rates is going to take ages...
 
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MichaelMeissner said:
Add explicit voltage level conversion. There are other current discussions about level conversion at this site, so you might want to look it up (the typical i2c converter that you can find lots of places has problems with high speed lights). In general for LED projects the 74LVC245 seems to be the best. but the through hole version is 20 (2x10) pin, if size is a consideration. For converting up to 4 lines, I like the level converter from pololu (2x5 through hole): https://www.pololu.com/product/2595
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onehorse said:
If you have unidirectional signals, the 74LVC245 is probably best.
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Why the 74LVC245 for driving 5v pixels from a 3.3v uC?

If it's running at 3.3v with the Teensy, it can drive its outputs to almost 3.3v (with very low current) but so can the Teensy, right? With higher currents - eg driving capacitance at high speeds, especially if the first pixel is some distance away - it's Voh is even lower.

I would have thought for unidirectional output, something like a 74HC125 running at 5v (or pixel voltage) would be useful. The Teensy should be able to drive it at 3.3v and it should be able to drive the pixels at 5v. One chip could potentially drive two SPI strings from the same uC SPI output (and two enable output pins) - or 4 WS281x strings.

What am I missing here?

PS: The 74LVC245 does look good for receiving 5V inputs to a 3.3v uC, especially if you want a bunch of them.
 
I don't think we can say whether level shifters are needed or not without some serious testing of what works and what doesn't.

The NeoPixel strips were very touchy about Voltage levels. Even with level shifters, most that I tested weren't good enough (Testing level shifters for running Adafruit NeoPixel strips from a 3.3 Volt Teensy).

The APA102 strips don't seem as sensitive to less-than perfect inputs, but I'm so far only powering them off a stable 5 V and feeding them data at a stable 5 Volts through a 74LVC245. I've yet to try them powered off a single lithium cell with data at 3.3 V.

If a shifter is needed, the TXS-0102 might be a good small one, otherwise I expect a 74xxx... will be worth testing. That's all on my list of things to try, but not until after Burning Man.
 
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i am in the process of a complete rebuild of my pixel poi and am heading down the li ion route. APA102 are on order, so not much to report yet, but the ws2811 ran happily (received the correct data, no glitching) for over an hour when using a phone battery for testing - 3.7v, 900mAh hooked up to the teensy Vin and directly to the power lines of the ws2811. Only 117 leds, but I was surprised that my calculations for current requirement were such a high over estimate, meaning that run time was longer than expected using mixed colour driving. Also, I have never needed to use a level shifter when using a 4.8v system for driving the leds and teensy together - 4.8v being 4xAAA rechargeable. Still, APA102 may be different, but looking forward to trying out a new much more compact and lightweight system with no removal of batteries with the one horse charger. a vid here: https://www.youtube.com/watch?v=hnrzNlFxj_4
 
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