G-Pendant data logger
Base Station & Coupler
Solution to hidden Status LED
As part of an effort to measure Rapid Eye Movement while sleeping
there's two things needed, one is the eye movement and the other
movement. REM sleep is very similar to being awake except
REM sleep there are no large muscle movements. The G-Pendant
is a simple way of logging head position while sleeping.
I have used the Hobo H-8
logger and like
it so got the G-Pendant from the same company.
G-Pendant data logger
The G-Pendant made by Onset
consists of a small PCB ( 1" x 1.5") housed in a small water proof
clear plastic can whose lid is sealed with an O-Ring. On the
is a PIC 16F690
micro controller, an Analog Devices XL330
3-axis accelerometer, an 24LC512
EEPROM, a reed switch, 2 ea. LEDs, 2032 buttton cell battery and
parts. But to use it you also need a computer coupler and
software which is included in the G-Pendant
When the battery is changed in the pendant be sure to install the
into the groove in the can. The battery should be visable on
groove side of the can. The label can be read without the
distortion from the groove. It's possible to install the PCB
down then the LED in the can and the base station will not talk to
The G-Pendant uses a 3 Volt CR2032
coin cell. It's voltage is recorded by default along with
Y and Z acceleration values. A good scale is 2.5 V min to
max when plotting. If you autoscale a plot the voltages will
set to display the maximum and minimum recorded values which is
clear as the above fixed values.
After replacing the battery be sure that the PCB goes back into
in the slot . Also be careful to get the O-ring in is groove
not pulled out.
The XL330 3-axis accelerometer IC is designed to run on less than
uA and expect that it's only turned on long enough to make a
measurement so the battery drain is very small.
25 Apr 2007 - have used for 40 nights about 10 hours/night or
4000 hours and the battery is still at 90%! I don't sleep
hours each night but often do not stop the logging until 10 to 12
after starting. This is a good example of both the improved
Analog Devices 3 axis accelerometer and the Microchip Technology
Watt" feature set on the newer micro controllers.
31 May 2007 - have continued to use every night and the origional
battery is still strong. 40 + 36 = 76 nights * 10 hrs = about 760
13 Jun 2007 - origional battery is still working fine 89 nights or
about 890 hours.
25 Jun 2007 - still working about 1,000 hours
Optic USB Base Station for Pendant &
The base station is USB powered so doesn't require a
active part of the base station is packaged in the same type clear
plastic can as the pendant and has an LED in about the same
place. It's a USB to optical interface. The base
plugs into the coupler plain end and the pendant plugs into the
that has the permanent magnet. The magnet activates a reed
in the G-Pendant causing it to look for digital data at the
interface LED. The groove in the coupler and the ridge on
the can is to
make sure the two interface LEDs are looking at each other.
The red blinking LED that shows through the hole in the label is
different than the interface LED.
The reed switch in the G-Pendant also serves a couple of other
purposes. When you start the newer Onset data loggers (they
it launching) there are options relating to when the logger starts
as right now, on the next even minute, at some specified time, or
in the field when the event button is pressed. In the case
G-Pendant the button is replaced by bringing a magnet near it.
In order to save pendant battery power the PIC controller powers
when there's nothing to do. When the time between
gets too short to allow sleeping between tasks the current drain
up. This is also why you will drain the pendant battery if
store the pendant in the coupler even when the base station is
disconnected from the computer. What happens is that the PIC
the pendant sees the magnetic field and wakes up and starts
the base station LED data which is not there, but it keeps looking
Interleaving synchronous data and asynchronous data in a single
storage file, 711/157 ; 707/102 - In a standard data logging file
header would contain the start data - time and the interval
data fields. That way no starage is wasted lodding a date
time for each data point. An event logger only logs the date
time when the event occurs and otherwise does nothing, for example
rain gauge may be implemented as an event logger but the
and barometric pressure would be data loggers. This patent
way to combine the two different types of data in a single file
The Hoboware Lite softeware that
in the kit supports setting the time interval, starting time/mode
what things will be logged and does the launching. It also
status mode that allows you to see real time data from the
G-Pendant. But the more interesting part is reading to a
plotting the results. I'm now in the process of learning how
use the plotting function. Not only does it let you plot
individual axis, but in addition the total vector or tilt in any
planes. Also things like battery voltage and various events
Onset has a patent on how they record events in a data
Note that when data logging you do not need to remember a time or
for each measurement. All that's required is to remember
started and the time interval between measurements. But if
event is to be stamped with a date & time a different format
needed and that's what patent 6826664
Interleaving synchronous data and asynchronous data in a single
data storage file
Although the G-Pendant has a reed switch that's used to start
in the field by using a magnet or empty coupler, that switch does
support event recording (that's too bad, it would be a nice
when long intervals are used between measurements).
Launching is the term Onset uses for
starting a data logger. The Launch window has a number of
fields. At the top there's an identification of the device,
serial number, a battery gauge, the number of times it's been
a text input box for a Description of the log.
In the Channels area there's a list of the possible channels with
a check box to select the ones you want to log.
In the logging interval area there are radio buttons for Fast or
mode. In normal mode there are text input boxes for Hours,
Minutes and Seconds. And if your logger supports Fast
(intervals shorter than 1 sec) there's a drop down list of 8
frequencies from 2 Hz to 100 Hz or a selection for Custom where
icrement/decrement window allows you to specify an interval in
Once you have set the logging interval and selected the channels
logged these two factors and the programs knowledge of the memory
for your logger are used to compute a logging duration. This
duration does not account for Events (button presses for those
that surrpot that feature. The G-Pendent does NOT support
The Launch Options are:
- Immediatle - the logger is connected to a computer and
should be started ASAP
- At Interval - launch at the next even minute
- Delayed - you enter a Year/Month/Day and Hour/Min/Sec and
logger will wait until then to start logging
- Trigger - the logger will wait until there's a long (3
button press or for the G-Pendant a long (3 second) exposure
magnet. Once the launch is done and Ready appears at the
of the screen the LED on the logger will flash once every 8
seconds. Right after the logger is triggered the LED
in a quick burst. For a logger with a button it's easy
to see the
LED burst, but for the G-Pendant you can not see the status
it's in the Coupler and the magnet used in the coupler does
not work to
start the G-Pendant when the G-Pendant is brought near it on
Last night I thought I had triggered logging, but did not
G-Pendant in the Coupler long enough and since you can not see
burst you need to count the time between LED blinks, which did
happen when I was tired.
Solution to hidden
a hole in the Coupler so that the status LED can be seen when the
G-Pendant is installed. This makes apparent some new things.
1) When the G-Pendant is in the Coupler the status LED blinks once
a second! That adds to the battery drain.
2) If it's been launched and left in the coupler it continues to
blink once per second.
3) When removed from the coupler the LED is blinking at an 8
4) If installed in a coupler (with or without the base station in
the coupler) the blink rate goes to once per second.
5) Now if the coupler is removed it will launch, i.e. the LED
burst of blinks within maybe 1/3 second of being removed.
If you remove it too slowly you will miss the burst.
after the burst the LED is at a 4 second interval, i.e. logging.
6) If the G-Pendant is put back into the coupler the LED blinks
per second and it's still logging. So a once per second
rate means the logger is in the coupler and may or may not be
10 Apr 07 - After stopping logging and downloading the data I shut
the software while the G-Pendant was in the coupler. The
LED was NOT blinking. Does this mean the G-Pendant is smart
enough to know to not look for data and so can be left in the
without the battery drain that it must have when the LED is
once per second? I think not because if the G-Pendant is now
installed into the coupler (base station connected to computer)
computer senses a new USB device and the status LED is NOT
blinking. So in the above cases where the status LED was
once per second the software was running.
12 May 2007 - Drilling a hole in each side of the coupler allows
the LED when you launch a G-Pendant go to the 1 blink per second
(confirming that it sees the magnet). This is good since if
pull it out slowly you will mis the rapid blink indicating that it
started logging. Not a big deal since you can then determine
blink interval and hence the mode.
Hint About Trigger Launching
If you choose the Trigger launch option and put the
into your pocket with a loose coupler, there's a good chance that
G-Pendant will get launched accidentally. One way to avoid
is to carry them separately, but that's not as conveinient as it
be. So just plug the G-Pendant into the base station side of
coupler. This will keep it separated from the magnet.
By drilling a hole on the base station side in the right spot you
see the LED on the G-Pendant to confirm that it's in the pre
25 June 2007 - It turns out that you
can do event recording with the Pendant, and also probably with
other Pendants. Whenever the Pendant is inserted into the
an event is date-time stamped. So if you plug the Pendant
the coupler (the base station is not part of this) the Pendant
the magnet in the coupler and records that event. So a
near the Pendant acts the same as the push button on other modern
the photo at left the G-Pendant is inserted into the Base Station
of the coupler. This is how I carry it after launch in the
logging on trigger mode. To record an event just unplug from this
and plug into the other side where the G-Pendant will see the
Now the question is what would be required in the way of an
electromagnet to trigger the Pendant?
There are two classes of
slow logging, where the time between measurements is 1 second or
and fast logging where it's less than 1 second. The latter
things like dynamic vibration or acceleration.
In my case I have the G-Pendant on a headband while I sleep.
This is related to studying REM
sleep. With a 30 second interval there are about 700
in a 6 hour sleep which is well under the max storage
Also after 4 nights the battery is still showing full.
Brooke's Home, Hobo
H8, Sensors, Page
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