Sudden Impact Wearables Design Challenge
Crown Tools - Helmet Impact Monitor
User Manual
by Doug Wong
The Crown Tools is a helmet mounted instrument to monitor head impacts that athletes might
encounter and transmit results via Bluetooth to an android smart phone.
This manual covers physical helmet installation, system operation, charging, and data reading,
including remote access via Bluetooth. The initial packaging is not intended to survive direct violent
impacts to the Crown Tools device itself, but rather it is intended to record direct impacts to the
helmet. If the Crown Tools is damaged by a direct impact, it may still be possible to download
recorded events via Bluetooth, including the event that damaged the Crown Tools. The Crown Tools
could be productized by shrinking it to fit completely in the channel on the helmet, making it less likely
to receive a direct impact. The case could also be made from polycarbonate, which would be much
less likely to sustain damage in a direct impact.
Installation of Crown Tools
The curvature of the Crown Tools was designed to fit a particular CCM helmet, but every helmet is
different and I also had to install it on a Itech helmet.
The method I use allows the helmet to be removed easily without no residue:
1. Cover the sensor installation area with black duct tape, stuck directly to the helmet - which can
be peeled off later.
2. Coated the underside of the Crown Tools with GE Silicone II (black) with enough silicone to fill
in any gaps between the curvature of the Helmet and the curvature of the Crown Tools
3. Spread a thin layer of silicone on the duct tape.
4. Press the Crown Tools in place, allowing excess silicone to squeeze out around the edges.
5. Allow the silicone to cure.
6. Tape the plastic edges of the Crown Tools to the helmet with black duct tape, leaving the
display and switch exposed.
Note1: It is critical for the area under the accelerometer to have full, bubble-free, silicone coverage.
Note2: The silicone does not form a great bond with the black side of the duct tape, so once it starts to
come off it can pop off.
Note3: The sticky side of the duct tape will not stick to silicone, so some of the tape should be stuck
to the PLA plastic of the Crown Tools case.
Removal of Crown Tools
Peel the duct tape slowly off the helmet starting at the back. This will eventually result in the Crown
Tools separating cleanly from the tape and the tape should leave no residue on the helmet.
Crown Tools System Operation
Before turning the Crown Tools on, it is essential to place the helmet or Crown Tools device on a
stable surface. When the device first turns on, the display comes on for 2 seconds, displaying
"CROWN TOOLS" and a 4 digit number, and then it goes blank. During this initial display period the
Crown Tools must be kept stationary because it is performing a self-calibration. Any accelerations
during this calibration period will degrade the calibration. The blank display is mainly to indicate that
the calibration is complete, but it also conserves a little battery power until the first impact is
encountered.
Power ON - slide the white power switch, located near the front left edge of the case, away from the
edge of the case. This can be done with a finger nail or a toothpick.
Power OFF - slide the white power switch towards the edge of the case.
Charging
The Crown Tools is wirelessly charged using a Qi
charger. To charge the device, simply plug the charger
pad into USB power and place the Crown Tools on the
pad. Proper alignment is achieved when the blue LED
illuminates as shown on the right.
When there is no device charging or the device is
improperly aligned, the led will be red as shown below.
Startup
When power is first turned on, the display will illuminate and display "CROWN TOOLS" and a 4 digit
number. This number is the current voltage of the battery in millivolts. Maximum battery voltage is
about 4200 millivolts, but anything over 4100 millivolts is a pretty full charge. Battery life tests have not
been performed yet, but the device has run for 3 hours with very little drop in battery voltage. The
nominal battery voltage is 3.9 volts - where it spends most of its discharge life, but it never went below
4.1 volts after 3 hours.
After the display comes on and then goes blank, the Crown Tools is ready to capture events and will
display any event that exceeds about 2 g's. A small tap on the device will cause an event to be
recorded, starting at event "0". The zero event is usually an intentional light hit used to verify the
device is working.
This is what an initial event might look like:
Display Legend
 The top number (0 in this case) is the event number
 The second number (200 in this case) is the peak resultant acceleration calculated using the
vector sum of all 3 orthogonal accelerometer readings (in g's x 10 so 62 = 6.2 g's)
 The last number (7631 in this case) is the integral of the acceleration (area under the resultant
acceleration wave form) in mm/s x 2. This roughly equal to twice the final velocity in a drop test
of equivalent energy to the impact.
Event Indication
After the first event, the display never goes off, but continues to display the last event. When a new
event occurs, the display updates and the backlight is illuminated for 1 second.
Maximum Event Count
The Crown Tools can record up to 50 events. These events are not overwritten if more than 50 events
are encountered, but the event counter continues to count any extra events and the last event data
(corresponding to the event counter) is displayed on the LCD. All recorded events are lost if the power
is turned off or the battery dies.
Recorded Events
Each recorded event has 4 parameters stored:
1. event number (0-49)
2. elapsed time (seconds since the device was turned on)
3. peak resultant acceleration in g's x 10 - as described in the display legend
4. equivalent velocity - as described in the display legend
Remote Data Access
The Crown Tools device can connect to any Bluetooth device running a serial port protocol (SPP)
terminal emulator program, such as the android app - Bluetooth Terminal V1.2. by Juan Sebastian
Ochoa Zambrano.
The Crown Tools are always ready to pair with a Bluetooth host - as long as the Crown Tools is
powered up.
The Bluetooth device ID for the Crown Tools is "98:D3:31:20:2A:24”
To pair the Crown Tools to a Bluetooth host requires a 4 digit pairing code which is "1234" for the
Crown Tools.
Once connected, all 17 Bluetooth commands from the host are single ASCII characters as detailed in
the following table:
Crown Tools Bluetooth Commands
Command Alternate
Character Character Command Description
0
Send event 0 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
1
Send event 1 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
2
Send event 2 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
3
Send event 3 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
4
Send event 4 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
5
Send event 5 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
6
Send event 6 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
7
Send event 7 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
8
Send event 8 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
9
Send event 9 acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
e
E
Send last event acceleration peak in g's x 10 and equivalent velocity in mm / second (x2)
d
D
List all events, 1 event/line: event #, time stamp (ET in seconds), peak acceleration, velocity
x
X
Send Current X acceleration reading in g's x 10
y
Y
Send Current Y acceleration reading in g's x 10
z
Z
Send Current Z acceleration reading in g's x 10
b
B
Send battery voltage in millivolts
a
A
Toggle LCD backlight on or off
Here is what a typical terminal program would look like on an android tablet:
The first command here is "3" - which was sent to the
Crown Tools.
The Crown Tools responded with
the peak acceleration (237) (which = 23.7 g's)
and
the equivalent drop velocity (5789) (which = 2894
mm/s)
The second command here is "d" which the Crown
Tools responded to by sending back 5 events.
The first event is:
0 12 271 6944
 The "0" is the event number
 The "12" is the elapsed time of the event
(12 seconds after power up)
 The "271" is the peak acceleration (27.1 g's)
 The 6944 is the equivalent drop velocity (3472
mm/s)