Sunday, October 10, 2010

Hacking an Infoglobe - part 2

In the first part, we saw how to open an Infoglobe.
Let's see now how to modify it for our purposes.

Infoglobe Modification

In the Andrew original modification, he added  a second IR LED, handled by an external generator, after disabling the original one.
It is actually feasible, but the big problem for this approach, is mechanical.
The original IR LED is mounted and glued in the optimal position to transmit to the rotating arm.
Basically the original Andrew circuit, is a duplicate of the original one already present on the Infoglobe, so it make logical to try to reuse the circuit already present instead to duplicate it.
Also, we don't need to optocouple our circuit, since it will be embedded in the Infoglobe anyway.

The first step to better work on the prototype, is to "bring out" from the Infoglobe, 4 signals :
  • VCC (+5v)
  • LED IR input (base) transisto
  • Infoglobe message generator
  • GND
It is possible to proceed in this way :
  • mount a 4 wire pin connector (DIN - RJ11 - ecc.) in the base (be careful to drill the hole for the connector, since it is better to don't take apart ALL the circuit)
    I used an RJ11.
  • remove the SMD resistor R117 (4k7 ohm)
    This resistor enter in the base of the transistor who is driving the IR LED. The other side is connected to the Infoglobe microcontroller.
  • connect 2 wires of the connector to the places where the resistor R117 was attached
  • connect 2 wires for the power supply (+5V - GND)

This is a schematic of the modification.

Is important to pay attention to the wiring, so to be sure to connect correctly the external interface (in my case I used an RJ11)
And this is a standard RJ11 color code:

In this picture I marked some optimal places to pick up the power supply and where to connect on the R117.

In my specific case, I reused an old RJ11 outlet 6 positions, using only the 4 central wires.
I used to connect the outlet, a phone wire using the standard color code.
So I had :

  • not used
  • black - to the IR LED transistor
  • red - +5V
  • green - GND
  • yellow - to the Infoglobe microcontroller
  • not used

Below, some pictures of the modification.
You can notice the black wire attached directly to the transistor, because removing the R117 resistor, the PCB was damaged.
Also it would be better to use a more thin wire than the one I used.
Attaching a square outlet in a curve box is not really easy and my mechanical skills are not very good.
Fortunately the hot glue helps to fix many imperfections and attach strongly the RJ11 outlet :-)
It is true this is just a prototype, the final version will not need holes since the ZigBee module and the circuit will be all inserted inside.

At the end of this work, I have now an Infoglobe modified, with 4 signals ported out, so to be able to experiment and design an interface.
In order to have the Infoglobe working as usual, I prepared an RJ11 plug with a 4k7 resistor between the pins 1 and 4 (the external ones) in order to allow the signal generated by the Infoglobe base to reach the IR LED.
This plug will be substituted by the MSP430 interface connection.

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