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BEC dc-dc power, can I program prop2 on battery? — Parallax Forums

BEC dc-dc power, can I program prop2 on battery?

IncVoidIncVoid Posts: 39
edited 2021-11-10 05:37 in Microcontrollers

Need some quick help, consulting if you will.
I got a cheap BEC from adafruit
Have some 2811 leds. JMs pixel driver and my p2 eval.

Im very much a peek and poke amateur here. typing on mobile so bear with me.

My gut tells me I shouldnt program the p2 while its battery powered by the BEC.
Will the lights be fine running off the BEC while prop is usb powered and programmed by the computer? the grounds will still be connecting to each other correct? as well as the 5v when signalling the leds. so im still iffy on it.

after programming:
I think the jumper on ldo vin 5v on the eval is for its own power, I dont wanna hook up the bec output to the prop that way, right? Do I wanna solder some pins into the aux 5v/gnd area, by the aux usb 2a connector. and plug the BEC there to battery power the prop?

also. i have two of the BECS. can i hook their outputs together? or should i keep them separate? I realize ill only have about 6amps max (thatll be hot), and I plan on doing basic math based on80ma for each led, and i can calculate my all on max brightness that way. But Im wondering if I'll have to keep the 5vs separate when powering both ends of the led strips.

anything helps. dont wanna fry my p2 or burn up one BEC with the other!

I cant figure out how to embed pics. I got all my stuff in hand. I know JMs pixel driver works with 2811bs for a fact. I hav hands on experience with a 12 led ring neopixel from adafruit but I just lit that while powered from pc, and debugged there. but here im gonna have upwards of 5 meters of leds. 150 leds on my 5m strip. dont wanna trip or brown out my usb on pc.

further along tonight. I see the schematics say use the port at my own risk. j502

I bit the bullet and powered it from the BEC, and the eval board lights up. no smoke. moving on.


  • Hi!

    Safe to power up the board using the 5V from your BEC, or pretty much any 5V power source that can provide enough current.

    You are right about hooking power into J502. That is the right place to connect aux power in. The 5V jumper you mentioned will only get power to the accessory headers, and not the regulators needed by the Propeller chip.

    You can program the P2 board whilst it's powered at J502. No problem. You can keep a USB cable connected to the PC-USB socket whilst power is provided via J502 or the USB-AUX socket. If you want to unplug the PC-USB programming cable and leave the board running (powered by J502/USB-AUX), then that's fine too.

    Joining the BEC outputs.... I've seen BECs that allow that, and others that don't. You'd want to check the BEC user guide for that detail, or ask the manufacturer. Although, likely one BEC would provide all the power you need for the P2 board ?

    That warning on J502 is due to those pins being "straight in" to the board. So it's up to the user to ensure the 5V & GND cables are connected the right way around, and that the voltage doesn't exceed 5V +-0.25V, or else things will fail rapidly! Also it wouldn't usually be a good idea to have a power source connected to both J502 and the AUX USB socket, so don't use that AUX USB whilst running power into J502.

    Good job on trying things out; no smoke zone :)

    Enjoy the experiments.

  • thanks for the reply! I can connect the gnds together? think they kinda have to be?

    I plan on having 3 strips on one BEC, and 2 strips and the prop on another. eventually. I think as long as the red wires, the Vouts arent dighting rach other ill be fine.

    I went and powered the strip off of the battery, but i got a lot of noise on the strip, at times being unprogrammable garbage in the leds. it has 4 wires. red and blk for the 5v/gnd , and another white and black. it looks like the black is just another ground. white is the signal.

    even unplugging the usb of the prop plug didnt help. but with the prop and strip both on battery, i can program from the pc and it runs fine. no noise on the strip. I was worried it was just noisey and id have to learn what caps to denoise with. on switching reg like this lil guy, i dont think its as simple as throw caps across it.

    I can safely move on to getting animations now.

    hosted on twitter. just using the ping ticks bounded in a range and scaled up to how many leds I have on this strip, threw in a lil remainder for the color cycling.

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