Activity Board: How could p26 fail?

John Kauffman · 2015-04-10 09:07

I have code (listed at bottom) that flashes p26LED then pin27LED - but 26 never lights. I swapped boards and on boards #2 and #3 the P26 works. I conclude that on board #1 either pin 26 or its LED is blown. I'm curious if problem is pin or LED.

To test LED I ran code from EEPROM of one line listed below. I connected 3.3 to 220 to jumper and touched jumper to side of smd LED. I got a faint glow on both SMD LED26 and 27. Conclude LEDs are OK.

main(){}

To test the pin I don't know of a way to connect a circuit on breadboard to P26 . Is access to the actual pin 26 possible? I suppose I could try touching a fine wire directly to the Prop chip's appropriate leg under a microscope.

Thanks.

#include "simpletools.h"
// breadboard circuit: p0>220>LED>GND
main(){                              
  high(0);pause(500);low(0);pause(500); 
  high(26);pause(500);low(26);pause(500);
  high(27);pause(500);low(27);pause(500);
  //  p0 LED works, p26 LED fails, p27 LED works
  // retested on 2nd, 3rd board - all work
}

Electrodude · 2015-04-10 09:16

One of the pins on the headphone jack is labelled p26. What if you send audio out of pin 26 and plug in headphones or a speaker?

Genetix · 2015-04-10 09:52

John,

Is this an old or new board?
If it's new then the LED could be backwards and if it's old then it could be a failed solder joint.

Is there continuity between P26 and the LED?
Note there is a Buffer chip between P26 and the LED (page 5 of the schematic).
https://www.parallax.com/sites/default/files/downloads/32910-Propeller-Activity-Board-RevA-Schematics.pdf

Do you have an oscilloscope?
Run a program that toggles P26 and put the probe directly on P26. You should see a square wave if P26 is good.

I'd be surprised if P26 is burned out and would put my money on a faulty solder joint.

Ken Gracey · 2015-04-10 11:52

John, I'd be happy to replace this board for you. Just drop me an e-mail with the request and send the faulty one back to me.

Ken Gracey

Joeldar · 2015-04-10 19:06

I just ran into a similar problem. Was having problems programming an SPI device on my activity board, moved it to different I/O pins and it worked just fine. Figured out pin 1 on the activity board was inop.

Joel

Activity Board: How could p26 fail?

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