Didj and Leapster Explorer TV Out

From eLinux.org
Revision as of 13:43, 21 July 2010 by Nirvous (talk | contribs) (Hardware Setup)
Jump to: navigation, search

Introduction

This how-to outlines the basic steps to enabling your Didj to send a composite video signal to your television. For the story behind how we got this working see rosincore.com

To-dos

Add user-space dual-screen support.

Add user-space external screen control.


Requirements

A Didj you are willing to disassemble and solder parts to.

Kernel compilation environment. For example:

Buildcross Didj Build Environment

Scratchbox Didj Kernel Build Environment


DJHI or similar mechanism to perform a UART boot or SD Card boot.

Breadboard

75 Ohm resistor

220pF capacitor (may be optional. this has been known to work with just the 75 Ohm resistor)

Composite jacks and or plugs

Hardware Setup

On the Didj

The LF1000 processor contains a current-driven digital-to-analog converter that can drive an external screen via CVBS (composite video). On the Didj, the DAC connection is exposed via Test Pad 6 (TP6) which can be found on the CPU side of the board.


Bga-closeup.jpg


To access TP6, you will need to remove the Didj main-board from the case. You may also find it more comfortable to work on TP6 with the LCD panel ribbon cable disconnected (its delicate, so be gentle as you pull out the ribbon cable)


Didj Mainboard Front.jpg


Solder a strand of Kynar, or an IDE strand, or similar small-gauge wire to TP6. (Make sure the wire is long enough to exit the case where desired.)


SolderingToTP6.jpg


Solder another strand of wire to ground. (ex: The metal on the cartridge socket is grounded.) (Make sure the wire is long enough to exit the case where desired)


Solder the end of the wire connected to TP6 to the middle pin of an RCA plug


Solder the end of the wire connected to GND to the outer ring of the RCA plug


Reassemble your Didj, routing the additional wires appropriately.


Filter circuit


Build the filter circuit as follows:

(Note the capacitors may be optional. This hack has been known to work with just the 75 Ohm resistor)

DidjTVOutSchematic.png


Connecting

Connect the side of the circuit with the resistor to the Didj, and the other side to your TV's Composite input jack.

Software Setup

The LF Kernel sources already contains all the code necessary to enable you to connect your Didj to a TV via a Composite Video (RCA-style) connection.


To enable this capability, you must first have a kernel cross compilation environment set up (see Requirements).


The adjustment itself is simple. If you have just set up your kernel compilation environment and are compiling for the first time, set up your kernel by running make menuconfig. This generates a file called .config .


Edit .config and toggle (or if its not present, add) the CONFIG_LF1000_DPC_DUAL_DISPLAY directive as follows:


CONFIG_LF1000_DPC_DUAL_DISPLAY=y


Make any other adjustments you want and then build your kernel.

Take the resulting zImage and load it onto the Didj using Uart boot (or if toy have LB1.4 set up, an SD card)


Thats it! Shortly after rebooting, you should see an image on both the LCD and your TV.

DidjTVOutPlasma.JPG

(Note: This has been tested with a NTSC television. It is likely that some driver reconfiguration may be necessary to enable PAL.)