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Precautions to ensure
that your KeyMaker USB and ThinkPad are not damaged
In order to avoid damage to your KeyMaker USB there are
certain precautions you MUST observe.
Your KeyMaker has electrical contacts on both sides, you
must ensure that no part of your KeyMaker USB board comes into contact
with any conductive surfaces such as bare metal or bare wires.
You should place down a piece of paper and place your
KeyMaker USB on top of it in order to avoid any electrical contact
which may damage your KeyMaker.
There is no danger of receiving an electrical shock from
your KeyMaker USB as the highest voltage anywhere on the board is 5 Volts
which is a safe voltage to touch.
If you like you can place your KeyMaker USB board inside
a plastic bag during use, the board does not get warm at all, so there is
no issue with ventilation.
The same precautions apply to your ThinkPad when you are
performing any operation and your ThinkPad is switched on, you must ensure
that nothing can short out by coming into contact with other parts, you
can use sheets of plastic or plain paper to make sure things remain
electrically isolated.
The 4 leads from the KeyMaker I2C connector are VCC,
GND, SCL and SDA.
GND is connected back to GND on your mini USB connector
and onto your PC or laptop.
VCC is connected to the 5V DC supply from your USB
connection in your PC, it then passes through a self reseting Pico fuse, so it is well
protected should you accidentally short it out, in 99% of use we do not
use the VCC lead anyway.
You do need to take care with the SDA and SCL leads
as they are NOT protected and can be damaged.
If you are careful and NEVER connect SDA or SCL to anything
other than the SDA and SCL pins of an EEPROM no damage will ever occur.
However if you accidentally make a mistake and connect
either SDA or SCL to GND or VCC on your KeyMaker Board or inside your
ThinkPad you will damage the KeyMaker USB SDA and or SCL I/O pins.
The reason is that the SDA and SCL I/O pins connect
directly to pins on the Microprocessor on your KeyMaker USB.
The SDA and SCL I/O pins MAXIMUM DC Current from either
the SDA or SCL pin is 40 mA, that is 40 thousands of an Ampere, a VERY
small amount of current.
If you exceed 40 mA you will damage the I/O pin and your
KeyMaker will not function.
You will exceed 40 mA if you directly connect SDA or SCL
to either GND or VCC anywhere on your KeyMaker USB board or inside your
ThinkPad.
Therefore you must double check that you do indeed have
the correct lead and you are about to connect it to the correct point
BEFORE you actually connect it.
If you want the luxury of being
careless, make serious mistakes connecting to an EEPROM and not cause damage, there is a way you can protect your SDA and
SCL I/O pins so that they cannot be damaged even if you accidentally
connect either to VCC or GND.
The protection consists of 2 x 180 Ohm resistors.
Very inexpensive insurance.
One 180 Ohm resistor is connected in series
with the SDA lead.
Another 180 Ohm resistor is connected in
series with the SCL lead.
Below are photos of how I modified my 4 way I2C lead to make
it safe against accidental contact with GND or VCC
The original 4 way lead, 2 x 180 Ohm 1/4 Watt resistors
Cut out a length of lead from the SDA and SCL leads and
solder 2 resistors in series, I used heat shrink which must be threaded
onto the cable BEFORE soldering
Heat shrink in place
Clear sticky tape wrapped over the heat shrink for added
strength
The modified 4 way I2C lead connected to KeyMaker USB
board
Disclaimer
I make no warranty that any of my
information is correct, or safe, or does or does not breach any warranty
clause, or anything else, it is up to you to decide if you will
follow all or any of the instructions to recover the Supervisor Password
from a TP. It is up to you to decide, I am not responsible for the
results or for any consequential or incidental damages whatsoever.
