PJRC MP3 Player

Display Board I/O Modifications

Here are some modifications to enable external devices to controlled and monitored by the display board.

Notes

In version 1 of the display software we added some commands to read and write to external I/O.  The idea of this was to enable backlight sense and control, but lots of other uses could be made of the pins.  It is too slow to do infrared remote reception by this mechanism unfortunately.  There are two options detailed here, the first is to retain the existing configuration, the second is to allow 1M bit flash devices to be used (I have found these easier to get than the 512k bit devices)

Procedure

This requires some a little soldering skill and a little manual dexterity.  You are unlikely to wreck your board, but if you do it is solely your responsibility, I take no responsibility for these procedures.

• Put something soft on your table and place the display face down

• Examine your board locate the CPU on your board, it is labelled IC3 and has an intel part number N80C32.  Locate pin 7 and 8, these are your I/O pins
  
  
  
  
  

• Using a knife or a small PCB drill, cut the tracks leading from these pins
  
  
  
  
  
  

• Reconnect the cut pads to either +5V (1st image) for a standard configuration or to +5V and ground (second image) for 010 devices.  The connection in the second image enables a 1Mbit (eg Am29F010B) Flash device to be used in the socket.
  
  
  
  
  

• Connect your external wires to the two pins now left unconnected.  Note that the command deliberately use active low as the CPU is capable of pulling enough current to turn a led on (~5mA).  Your should not drive anything requiring current from this pin, the most it can deliver is about 5 micro (ie. 10E-6 not milli) amps.  You should use a current driver eg DS75452N to drive any external devices like the backlight power supply.  I used the last two spare pins on the 20 pin connector to the keyboard/driver board.
  
  
  
  
  

• The DS75452 is an open collector driver. Wire it to the ground of the inverter and connect JUST the ground of the battery to the board ground. The +ve of the battery stays connected ONLY to the +5V of the inverter.
  This assume you want to continue to drive the inverter from something other than 5V. See below for a suggested circuit for connecting the driver to the display.

                              +5v
                           |
                           |8
                       --------         | -ve of inverter
                     1|        |3       |
from display      ----|        |--------
------------------|   | 75452  |
                  ----|        |
                     2|        |
                       --------
                           |4
                           | 
----------------------------------------- battery -ve

(nb. most of these images were done with a low cost scanner - hence the quality is at best ok)