I’d like to get some feedback on my plan for getting four hardware SPI lines on a teensy 3.2 with the attached design, to power APA 102 Led strips.
I have 4 separate groups of these LED strips, in each group there are 2 strips, with the data and clock pins daisy chained. Each LED strip has 103 leds in it.
I would use a level shifter to change the voltage of the signals from 3.3v to 5v. In this design, I’m using data pins 7 and 11, and clock pins 13 and 14, and converting them to 5v using the level shifter.
In total, there will be 824 LEDs. I plan on getting a 5v, 10a power supply.
Will this be enough power?
Will the Teensy have enough memory for these LEDs?
Will issues arise from connecting the 3.3v ground of the teensy to the 5v ground of the power supply?
Should the splitting of the data and clock pins happen before or after the level shifting?
Is 26awg wire sufficient for this power?
Power depends on how much light you want to use, but it’s not likely enough power. By my math, at full white, that’s nearly 50 amps at 5V (824 * .06 which I believe the APA102 LEDS consume roughly, but I could be wrong). So, even if you cut brightness by 80%, you’re still at the limit of your power supply. You would also have power drop issues by the time you got a few hundred LED’s in, so you won’t have 5V going through the strip like you think you would.
I would suggest powering strips by either
Powering each strip with a 5 amp brick and using FastLED to keep power max fixed for you
or
Power 2 or 3 strips together, each with a 10 amp brick. Still use FastLED power management.
Common ground. Teensy, grounded to strips, grounded to power.
I think no matter what you do, you’ll have power issues with this plan.
In this case, ground is ground, as long as it’s common to the supply.
I don’t think you need to level shift the teensy if you power it with 5V as well. Maybe someone else can weigh in on that. I don’t remember level shifting for Neopixels or APA strips, but I could be wrong, it’s been a while with that micro for me.
@Peter_Buelow teensy logic is 3.3v and could drive the pixels but for best results the level shifter is recommended . Great info on pixel power requirements.
Looking at your wiring for the level shifter… It looks like you have signal in and out wires mixed in both sides? Maybe I’m not looking close enough, but double check that, as all the inputs are on one side and outs on the other.
Peter is right, you really will probably want a power supply bigger then 10A with that many LEDs!
Ideally you want to power the LEDs to whatever brightness you need and still have a bit of a safety margin above that.
Even in case the leds are just lighting at 10 percent there is still the PWM running which means the leds draw the full current for a very short time. (Look at the WS2812 Jitter Video I showed some days ago.) Usually they are not synced but there is also nothing that prevents part of the leds to blink synced enough to temporary collapse the power supply. Some BIG capacitors might help to avoid this. I would go for several small power supplys which together can deliver the required 50 A. Enough memory? Yes. Connecting all ground together? Yes, sure.
Will the Teensy have enough memory for these LEDs?
Yes, I have used a Teensy to address 5000 LEDS without issues.
According to FasLED’s documentation each LED takes 3x bytes. 824 LEDs will take around 2.4k of ram. Teensy 3.2 has 64k of ram. So yes, you will have enough ram for the LEDs and some logic.
