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Safety Precautions to ensure
that your KeyMaker Board and ThinkPad are not damaged
In order to avoid damage to your KeyMaker
Board as well as the ThinkPad you are using it on, there are
certain precautions you MUST observe.
If you ignore these
precautions you will join the 3% of customers who bought a KeyMaker board
- ignored these precautions and damaged their KeyMaker Board by
being careless - then had to pay to have it replaced - and lost a lot of
time in the process.
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 prefer you can place your KeyMaker USB board inside
an Anti-Static 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 BEFORE 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.
You MUST NOT allow the SDA and SCL leads
from any KeyMaker KMX1 or KMX2 to come into contact with ANYTHING other
than the correct SDA and SDA EEPROM connections points and ONLY AFTER;
You have traced the wire
you are using for your probe right back to the label on the I2C header on
the KeyMaker board which reads SDA for YOUR SDA lead and reads SCL for
YOUR SCL lead.
You have absolutely
confirmed that you have correctly identified the SDA and SCL connection
points on your ThinkPad System Board.
3% of customers who purchased a KeyMaker
Board have somehow managed to damaged their KeyMaker board.
NOT ONE of those customers can tell me
exactly what he or she did to damage it.
I have tried all sorts of seriously
ridiculous ways to damage a KeyMaker board and I have NOT BEEN ABLE TO
DAMAGE ONE !
I only tried MILDLY STUPID THINGS like
connecting a solid 9 Volt source to SDA and SCL - theoretically that
should have damaged the I/O pin on that KeyMaker powered from 3.3 Volts,
IT DIDN'T.
Your KeyMaker board is a delicate piece
of equipment, treat it with respect.
Do NOT experiment or connect to anything
if you are not certain you have the correct connection points identified.
There are voltages much higher than 3.3
Volts inside your ThinkPad, in fact up to 20 Volts.
20 Volts is not a danger to YOU but it
is to the KeyMaker KMX1 or KMX2.
Connect SDA and SCL
leads ONLY if you have double checked and are CERTAIN you have correctly
identified SDA and SCL connection points
The above is VERY IMPORTANT - don't ignore it else
you WILL damage your KeyMaker KMX1 or KMX2 board and that is expensive,
wastes a lot of time and is not much fun.
The 4 leads from the KeyMaker I2C header 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 comes from the 5V DC supply from the
Mini USB cable connected to a PC or Laptop, it then passes through a 3,3V regulator and a self resetting Pico fuse, so it is
reasonably well
protected should you accidentally short it out, in 99.99% of use we do not
use the VCC lead anyway.
You 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 connection points of the EEPROM inside a
ThinkPad no damage will ever occur.
However if you are careless and connect
either SDA or SCL to GND or VCC on your KeyMaker Board or some higher
voltage point inside your
ThinkPad you will damage the KeyMaker 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 SAFE DC Current
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 a voltage source higher than the 3.3 Volts powering your KeyMaker.
Therefore you must double check that you do indeed have
the correct lead and you are about to connect it to the correct connection
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 a voltage SLIGHTLY HIGHER than 3.3V, this will NOT save your KeyMaker if you do
something really dangerous like connecting the leads to high voltages!
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.
Or you can use the KMX-LCD
which has the 2 protection resistors already fitted.
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.
