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RPi + OSMC Does using an Arduino make sense?

Discussion in 'Hardware Support' started by Rabid_Child, 24 August 2016.

  1. Rabid_Child

    Rabid_Child New Member

    Messages:
    4
    Hardware:
    RPi1/Zero, RPi2, RPi3, +Arduino
    My Hyperion setup has been defunct for awhile now due to a failed USB Video Grabber. However I want to bring it back to life and I would like some guidance.

    Previously, I was running a Raspberry Pi 1 running OpenElec with WS2801 LEDs connected to the SPI. This is what powered Hyperion. I used a Raspberry Pi 2 as my media center and thus pretty much everything was done through the USB grabber. One of the reasons I did it this way was because I wanted easy access to my media PC and having it stuck to the back of the TV was not easy access. I went through a lot of frustration setting it up initially because I ran a long cable from the SPI through the wall and out to the LEDs. It didn't work. It was frustrating because it worked perfectly in the test phase of the project. I eventually realized it was the long cable causing the problem. The signal couldn't travel that far. So I had to use a short cable and stick the Pi behind the TV. That is why the 2nd Pi came into being.

    Anyway, now I'm thinking of rebuilding it using APA102 LEDs and I was curious if using an Arduino might alleviate the issue I had the last time around. Can I connect to the Arduino from a USB hub? Or must it be direct from the PI? And can I use an LED strip with more than 30 LEDs per meter? I don't know off hand how many were on the strip I saw on Amazon but it was a whole lot more than what my WS2801's had. And finally, and perhaps most importantly, does the performance suffer from adding in this extra piece of hardware?

    Thanks much.
     
  2. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    The issue you had was probably signal voltage levels.

    Did you have a level shifter ?
    The LEDs really need signaling at 3.5v but the pi only outputs 3.3v

    An arduino would help, but mostly because they use 5v IO rather then 3..3v.
     
  3. Rabid_Child

    Rabid_Child New Member

    Messages:
    4
    Hardware:
    RPi1/Zero, RPi2, RPi3, +Arduino
    I did not have a level shifter. Clock, data, and ground went directly to the pi SPI and power came from a desperate 5v 10amp power supply.

    I was looking at these Mokungit 1M APA102 Smart led pixel strip, 144 leds/pixels/m ,IP65 waterproof DATA and CLOCK seperately DC5V White PCB https://www.amazon.com/dp/B019NZ0HS2/ref=cm_sw_r_cp_apa_L8hWxbZWRHFKW

    That's making the assumption that more is better. Is that a correct assumption and would these work or should I stick with less LEDs per meter?

    I should specify I suppose, it is for a 55 inch TV. I need to figure out the required length yet.
     
  4. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    Mine are stuck to the rear of the tv around the border and angled out 45degrees.

    The tv is about 8 cm away from the wall.

    119 Ws2812 LEDs @ 30 per metre was sufficient to get no gaps on the wall
     
  5. Rabid_Child

    Rabid_Child New Member

    Messages:
    4
    Hardware:
    RPi1/Zero, RPi2, RPi3, +Arduino
    Yeah, I never had any gaps in my old setup either, I just thought that more lights would allow for a truer depiction of what was on the screen. More granular.

    Regardless, that is really only a secondary consideration. The main purpose of the question is will I gain any advantage by using the arduino? Will performance suffer? Can I use a long USB cable between the Pi and the arduino?
     
  6. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    I don't think an arduino will help much.
    It will slow the max frame rate a bit as most of them have to receive a whole frame, buffer it and then send it to the LEDs.

    If you're ok with a soldering iron make a 74HCT chip level shifter.

    74hct125, hct245 and many others make good buffers / level shifters.
     
  7. Rabid_Child

    Rabid_Child New Member

    Messages:
    4
    Hardware:
    RPi1/Zero, RPi2, RPi3, +Arduino
    I'll read up on that then. Thanks for the input.