Spin Code & the Phantom LED

Humanoido · 2010-08-17 05:56

Using the Demo Board, can someone tell me why this code lights up the yellow LED on pin 20 and a phantom LED on pin 21 which is half as bright? Thanks in advance.

Humanoido

'' DEMO200.spin for the Demo Board
'' Set yellow LED on pin 20 to output and blink
CON
  LED      = 20                              ' I/O pin
PUB LEDBlink                                 ' Main method on/off signals
  dira[LED]~~                                ' Set pin to output
  repeat                                     ' Loop
    ! outa[LED]                              ' Change pin state
      waitcnt(clkfreq / 4 + cnt)             ' Wait

Ron Czapala · 2010-08-17 06:09

I had the same issue. It is caused by the resistors between them wired to the VGA connector. To avoid the problem, make the all the LED pins outputs e.g. dira[16..23]~~

Check the schematic http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropellerDemoBd-RevG-Schem.pdf

Toby Seckshund · 2010-08-17 07:26

On one of my homemade "DemoBoard" I put two diodes, in series, from the R,G and B feeds from the 15 way (Anode) down to ground (Cathode). The 1.4V is too small to allow the backfeed to the 1.8V LEDs and too high to affect the 1.0V VGA signal.

Humanoido · 2010-08-17 07:33

Ron Czapala wrote: »

I had the same issue. It is caused by the resistors between them wired to the VGA connector. To avoid the problem, make the all the LED pins outputs e.g. dira[16..23]~~
Check the schematic http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropellerDemoBd-RevG-Schem.pdf

Ron, thanks, that worked perfect. Here's the working code.

Humanoido

'' DEMO2.spin for the Demo Board
'' Set a yellow LED on the VGA circuit to output and blink
'' Choose p16 - p23
CON
  LED      = 19                   ' I/O pin for on/off signals
PUB LEDBlink                      ' Main method to send on/off signals
dira[16..23]~~                    ' Make the all the LED pins outputs to prevent phantom LEDs   
  repeat                          ' Loop
    ! outa[LED]                   ' Change pin state
      waitcnt(clkfreq / 4 + cnt)  ' Wait

Humanoido · 2010-08-17 07:36

Toby Seckshund wrote: »

On one of my homemade "DemoBoard" I put two diodes, in series, from the R,G and B feeds from the 15 way (Anode) down to ground (Cathode). The 1.4V is too small to allow the backfeed to the 1.8V LEDs and too high to affect the 1.0V VGA signal.

Toby, this is brilliant. It sounds like a plan for Parallax to incorporate in the next Demo Board Revision.

Humanoido

Spin Code & the Phantom LED

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