Multiple Teensy 3.1 -- Do +5V and Ground need to be tied together?

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baisoku

baisoku

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I am driving 24 5m 60 LED/m strips with 3 Teensy 3.1 / OctoWS2811, based off the VideoDisplay sample, with pixel data streamed from an external USB source and one Teensy being the master and driving framesync to the other two. I am powering the Teensy boards via the +5V power supplies used for the LEDs (not USB cable).

My setup looked like this before i started tying the sync signals together:

IMG_7206.jpg

The SYNC pads of each Teensy need to be tied together, but what about the GND and +5V? When i was doing testing before setting up my rig, i didn't have anything attached to GND, but i'm wondering if those need to all go to the power supply ground, and if so, if they need to be tied together. The +5V on each Teensy is running a separate line to the power supplies.

Sorry, sort of an EE newb.

Thanks,
--matt
 
Yes, the grounds must be tied together, if you tied the frame sync together.

The 5V lines do not need to be tied together, but you can if you'd like to power all 3 from the same 5V power.
 
I hope you'll post some photos when all 7200 LEDs are running! Questions about building bigger displays come up regularly, so pictures showing the build details of a working setup with more than 4320 (the lastest I've personally built) are always really nice.
 
So just to be clear -- like this:

IMG_7206.jpg

Thanks for the help. And yes, i will post pictures when things are up and running.
 
Yup, cut VIN/VUSB.

I think i found my major problem -- i was running the strips directly to +V on the power supply, but didn't connect the strips to -V on the supply, just to the ground on Teensy. Rookie mistake. Now 80% of my strips work -- i think i just have bad connections to work out.
 
All strips now work. Tested the voltages at each teensy pin, and was getting reasonable values (around 1volt), so i knew none of the teensy's were defective. Tested +V at the connections to LEDs and those were all 5V. Tested the data lines at those connections, some were 0. It turns out that my CAT6 cables were defective. With 16 of the 24 strips running, i'm pulling < 400 watts at full white. That is WAY below what i was expecting. We budgeted for a max of 1200 watts, and looks like we will be below that, which is great because i think our Honda 2k generator will run in eco throttle mode if we stay under 1200.

We are running 10-15 foot heavy-ish gauge wire (it's shielded 4-strand electrical, we're obviously only using 3) from the CAT6 to the actual LED strips. This isn't causing any problems, which is a huge relief. The only issue we have now is voltage drop across our 5m long strips. It's only really visible at full white (which we are not going to ever be set to), so we will either a) run additional power lines to the terminating ends of the strips, or b) not care. :)

Excited to post some photos once i've cut all the 5m strips into their multiple segments and wire them all up.
 
Glad it's working. These big LED projects can be quite a challenge, so it's always awesome to see someone pull it off well.
 
Thanks. Yeah, it's been far more complicated than our rig last year that just used 5050's and all we had to do was hook them up to 12V
 
Oh, one final question. The OctoWS2811 library page says this:

A strip of 60 LEDs can draw about 3 amps of current. Each strip should have its own connection directly to the power supply, using #22 or larger wire to avoid loss of voltage. Power can travel through about 2 meters of LED strip. If longer strips are used, both ends should be connected by wires directly to the power supply.

I assume "connected by wires" means "connected by both +5V and ground" to the power supply?
 
Everything is working properly and we have packed for Burning Man. Can't wait to share photos with you and a writeup of our development log. It's been a hectic build, but Teensy / OctoWS2811 have been indispensable, as have the great forum response.

We are running WAY under budget for the 7200 LEDs, not even close to our 1000W budget. Not sure how that happened, perhaps our back-of-the-envelope math was off by a lot, but we'll take it.

We wrecked one of our Teensys tonight screwing the cable enclosure into the frame of our vehicle, but had a spare, and ordered two more "just in case," because everything goes wrong on the playa and we like to have at least 1.5X what we need.

Pictures in a couple of weeks.
 
Ok -- make one mistake. We toasted one Teensy last night, and replaced it with another Teensy 3.1 / OctoWS2811 pair. But i realized after i connected it that i had forgotten to cut the VUSB/VIN trace. The other 2 Teensys have this trace cut, as we're powering them from the LED power supplies. And the Raspberry Pi is driving them over USB.

Is this going to be an issue? If so, i'll need to replace this new one with another Teensy / OctoWS2811 pair that i don't forget to cut the VUSB trace before i solder them together. :(

Thanks.
 
I'm not fully read up on the Teensy 5V supply circuit but my understanding is that the Teensy 3 doesn't care as long as the onboard reg has more than 3.7V arriving at it with respect to the ground pin, so having two lots of 5V is not actually a problem there. What is going to be interesting is at the USB hub which is now running the LEDs in parallel to your main PSU. A range of different things can happen here with varying amounts of smoke, but with sane power supply design in the hub it hopefully won't have done anything permanent, though actual USB data coms in this condition would have been interesting. The big concern is if your main 5V supply spikes high and feeds back through the hub and into the Pi.

If the underside of the Teensy is no longer accessible the ugly solution is to cut away the USB cable sleeve and clip the red wire. Just keep track of the abused cable if it goes into another project.

Have fun out there.
 
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