Building a GLOBE Sun Photometer (pc board V3.0)
Building a GLOBE Sun Photometer (pc board V3.0)
The GLOBE Program establishes specifications for
instruments.
However, GLOBE does not sell instruments nor does it
officially endorse instruments manufactured and/or sold by others (including members of the Science Team).
Most GLOBE protocols use readily available commercial materials and instruments. However, the situation for the
GLOBE sun photometer is somewhat different because no commercial source exists.
This document describes how to build a sun
photometer that meets the specifications established by the Science Team. Most components are
commercially available, but the printed circuit (PC) board and LED detectors should be obtained directly
from the Science Team. The parts suppliers listed below include those used by the Science Team in developing the
current version of the GLOBE sun photometer, but the parts are available from other suppliers, too.
Although it is possible to build a GLOBE sun
photometer "from scratch" (except for the LED detectors) a much easier approach is to work with parts identical to those used by the
Science Team. A complete kit of parts, including a pre-drilled case and battery but NOT including the
digital voltmeter required to monitor the output from the instrument, is available for $35
(check or money order from a U.S. bank or credit union only), from:
David R. Brooks
2686 Overhill Drive
Center Point
Norristown, PA 19403 USA
These instructions do not include general information on electronic construction,
soldering techniques, or safety precautions, because they assume knowledge of and practical experience with
such matters. It is especially
important for students doing any kind of electronic construction to be under adult supervision for both practical and
safety reasons. A soldering iron can cause serious burns. Some of the components of the GLOBE sun photometer are very
heat-sensitive and can easily be destroyed by overheating during construction. Careless soldering techniques can produce
solder bridges and/or cold solder joints, either of which will lead to an instrument that will not be work. Electronic
components must be installed properly, including observing the polarity of some components. Neither the
Science Team nor the GLOBE Program can assume responsibility for improperly assembled instruments, and I cannot promise
to offer advice or help past that which appears in this document.
Having issued these caveats, it is nonetheless true that I have found construction of
a GLOBE sun photometer from a kit of parts to be a perfectly reasonable undertaking for high school students.
Certainly, commercial instrumentation plays an
essential role in making environmental measurements. However, I believe it is a valuable experience for students
to make their own instruments whenever possible, as this enhances their understanding of and appreciation for the
challenges of making reliable measurements. I have worked with several
groups of students and teachers to build
GLOBE sun photometers. These experiences show that it is rare to find students or teachers with electronic construction
skills. In every case, it has been necessary to provide a tutorial on electronic construction, some practice
materials and components, and careful supervision of the process. It is easier to work in pairs, so it makes sense for
each pair of participants to build two instruments.
A completed instrument must be calibrated. This
is a challenging task and, at present, the Science Team is the only
source of calibrated GLOBE sun photometers. It is an interesting exercise for high school students to
perform a "Langley plot calibration" (as described elsewhere on my web site), but such calibrations will not
be reliable unless they are done at sites (usually high elevation sites) with very stable atmospheric conditions.
The Science Team's goal is to try to support all
serious efforts to collect aerosol data with the GLOBE sun photometer.
If you build your own sun photometer, you are invited to discuss calibration issues with the Science Team before
you undertake an aerosol measurement program. The good news is that it is possible to take measurements now and
calibrate your sun photometer later. It is even possible to guess at an approximate calibration by taking measurements
and estimating sky conditions through careful observation. GLOBE's computers will not accept measurements
from an uncalibrated instrument, but you can work directly with the Science Team.
Parts
Item description and source
Case, 2"x3-1/8"x6", plastic
Do not
substitute a case of a different size and do not change the location of the printed circuit board inside
the case, as described below.
SPDT toggle switch (2)
For the on/off switch, one terminal of one of the SPDT switch is not used.
9V battery snap connector
screws: (2) #6-1/4" pan head Phillips sheet metal
Screws can be round head or pan head, Phillips
or slot, but I find Phillips head screws easier to work with. The
sheet metal screws are for fastening the L-brackets (corner irons) to the top of the case.
pin plug jack: (1) red and (1) black
(2) 1" x 1/2" zinc- or brass-plated corner irons (L-brackets)
These metal brackets are typically sold packaged
with wood screws, but the sheet metal screws listed above should
be used to fasten the brackets to the case.
PC board
You should use the PC board that has been
custom-designed for the GLOBE sun photometer, which is available from
the Science Team. In principle, it is possible to substitute a standard perf board configured for dual inline package
(DIP) components, but this is not recommended.
op-amp, Linear Technology LTC1051CN8
Op-amps typically are available in more than one
package configuration. The CN8 specifies an 8-pin dual inline
package (DIP) configuration. Although other op-amps can be used, substitutions are not recommended.
LED detectors: Hewlett-Packard (Agilent) HLMP-D600
emerald green, or equivalent; HLMP-3762 high intensity red, or
equivalent
The LED detectors are the most critical
components in the GLOBE sun photometer. The spectral response of these
detectors has been studied extensively by the Science Team. In order for a sun photometer to be approved for use in the
GLOBE program, its detectors must be obtained directly from the Science Team.
resistors: 2.0 Mohm, 1/4-Watt, 5% carbon film; 5.6 Mohm, 1/4-Watt, 5% carbon film
Different resistance values may be included with your kit. This is based on
continuing instrument development by the Science Team and will not adversely affect the performance of your
sun photometer. In any case, the larger of the two resistors (5.6 MOhm, for example) is always for the red channel
and the smaller (2.0 MOhm) is always
for the green channel. You can determine the value of resistors supplied with your kit by interpreting the colored bands
painted around the body of the resistor. Here's a web link to an explanation
of the color code.
capacitors: 0.1 uF ceramic disc (1), 220 pF polystyrene or ceramic disc (2)
The voltage rating and tolerance of these
capacitors are not critical.
hookup wire, 22 gauge solid or stranded
black, approximately 15 cm (6")
red, approximately 15 cm (6")
green, approximately 5 cm (2")
Stranded wire is OK, but it is somewhat more difficult to work with in the small holes of the PC board and the
small terminals of the switches. It is easy to "nick" solid wire when you are removing insulation from the ends, which
can cause the wire to break after it's soldered in place. My personal preference is solid wire.
cyanoacrylate glue ("superglue") or two-part epoxy
For corner irons. This is not included.
You can get this glue or epoxy at a hardware or home improvement store.
9V battery, standard rectangular
Any 9V battery should last many months in normal
use. Alkaline batteries are more expensive than other types and
are not required. You can use rechargeable batteries in this application, but it may not be worthwhile because
of the very long life of regular batteries.
Equipment/tools
soldering iron
25-Watt with small pencil tip. (Do not use
any kind of "soldering gun" or a soldering iron with a power rating of more than 30 watts.) I use a soldering iron
switchable between 15 and 30 Watts. The 15-Watt setting is for work on the PC board and the 30-Watt
setting is for the switches and connecting the output wires to their pin jacks. To minimize the chance for
accidental burns, a cage-type soldering iron stand is highly recommended.
solder
This must be rosin-core solder specifically
intended for electronic work. I find the most widely available diameter,
0.062” (1.6 mm), to be too large for work on this PC board, so I always use 0.032” (0.8 mm) diameter solder.
Lead-free solder is available if you prefer to use that, but it is significantly more expensive.
screwdrivers
Phillips for case screws and Phillips or
straight blade for battery and corner iron screws.
pliers
Regular, needle nose and diagonal cutting
small craft knife
This is needed to cut away the aluminum tape
around
the sunlight aperture.
small straight-bladed knife or wirestripping tool
forceps or spring-loaded clip-on heat sink.
(optional)
For holding parts and wires in place. Surgical forceps
will also work as a heat sink -- these are often available from tool suppliers. Spring-loaded clip-on aluminum heat
sinks are often included with soldering iron kits.
magnifying glass (optional)
This is handy for examining your solder connections on the PC board.
digital voltmeter
Any digital voltmeter or multimeter will do. One possibility is RadioShack's
Model 22-802 digital multimeter (about US$25). It has an
auto-ranging DC volts scale and is small enough to fit into a shirt pocket. It is also small enough to be attached to your
sun photometer with Velcro tape so one person can make measurements easily. Another possibility is Kelvin Electronic's
50LE digital multimeter (about US$8, see www.kelvin.com). This is a very inexpensive digital meter that appears to be satisfactory for this
purpose.
The voltmeter is needed both to test
your sun photometer during construction and to make measurements with a completed instrument. An analog voltmeter
is not accurate enough to use for these measurements.
Step-By-Step Instructions for Building a GLOBE Sun Photometer
The schematic diagram for the GLOBE sun photometer is shown at the right. This diagram
uses standard symbols to show how the circuit operates, but it is insufficient as a guide to actually building such an instrument. If you do not have any experience with electronic
construction, get help from someone who has. This is not a
difficult project, but it is easy to make mistakes and VERY difficult to correct those mistakes later! It may
be a good idea to practice soldering some components before tackling this project. Buy a piece of "perf board" (available
at RadioShack and other electronics stores)
and a few resistors and capacitors and practice soldering them.
The GLOBE version 3.0 printed circuit (pc) board used provided with the kit is the same board used by the
Science Team for its own instruments. It is a multi-purpose board (including space for two additional detectors).
Consequently, not all the connections on the board are used for the GLOBE two-channel sun photometer.
As you go through these assembly instructions, it is important to use only the indicated connections on the pc
board. The accompanying photos are important guides to where parts do and do not go.
In some of the steps below, you are instructed to
strip the insulation off the ends of wires. You can do this
with a small knife or a wirestripping tool. In either case, if you are using solid (rather than stranded) wire,
you must be careful not to "nick" the relatively
soft copper. Once the wire is nicked, it may break when it is bent. Unless noted otherwise, you should
strip about 6 or 7 mm (1/4") of insulation of the end of the wire. Both ends of the wire should be stripped even
if a particular construction step involves connecting only one end. If you haven't done this before, practice on
some pieces of wire.
A. Prepare the Channel Select Switch
There are two SPDT (single-pole, double-throw) switches supplied with the kit.
One will be prepared now and the other will be used later.
It is easy to overheat the solder terminals on
these small switches, so be prepared to work quickly.
Test the "feel" of the switch action before you solder the wires. If the action changes
significantly after you connect the wires, the switch may be damaged.
Cut and strip three pieces of wire:
4 cm (1-1/2") red wire, with one end stripped 1 cm (3/8")
4 cm (1-1/2") green wire
4 cm (1-1/2") red wire
Using needle-nose pliers, form a small hook in one end of
each wire. For the first (red) wire, the hook goes in the end with 1/4" of insulation stripped off.
Connect the hooked end of the
first (red) wire to the center terminal of the switch and gently crimp the hook around the terminal.
Solder it in place. In the same way, connect and solder the green wire to one of the
outer terminals and the remaining red wire to the remaining outer terminal. Make
sure that none of the wires are touching adjacent wires or terminals.
B. Wire the Printed Circuit Board.
The photo shows an older version of the pc board. On newer kits,
the top corners will be square and the bottom corners will be slightly broken. This is to allow the
board to fit in the channels in the sides of the case even if there is a little cement at the bottom of the channel.
(The case sides are cemented in place.) The copper traces on this PC board are fragile, so you must be careful not to
overheat the connections. Parts mounted on the PC board are
always inserted from the printed (front) side of the board and soldered on the back side.
For steps 1-5, the direction of the component leads does not
matter. The components should be mounted close to the front surface of the
board.
1. Solder the 2.2 MOhm resistor (red-red-green, or the smaller value of the two resistors provided)
at component position R1. Do not overheat the resistor.
Trim the excess resistor leads from the back of the pc board.
NOTE: The resistor values supplied with your kit may
be different from 2.0 and 5.6 MOhm. (In the photos shown in these directions, R1 is 2.2
MOhm (red-red-green)). Regardless of the values, the smaller
of the two is always R1 and the larger is always R2. Click here for a
resistor color code chart.
or do a search for "resistor color code" on the web.
2. Solder one 220 pF polystyrene capacitors at component position C1. Do not overheat the capacitor, as you
may actually melt the plastic housing. Trim the excess capacitor leads from the back of the pc board.
3. Solder the 5.6 MOhm resistor (blue-green-blue, or the remaing resistor) at component position R2. Do not
overheat the resistor. Trim the excess resistor leads from the back of the pc board.
4. Solder the remaining 220 pF polystyrene capacitor at component position C2. Do not overheat the capacitor.
Trim the excess capacitor leads from the back of the pc board.
5. Solder the 0.1 uF ceramic disc capacitor at C5. Trim the excess leads from the back of the pc board.
For steps 6 and 7, the orientation of the
components is critical. Do not reverse the pins of these components!
6. Solder the op amp at component position U1. The notch and/or white line printed on the top of the op amp case must match the
position of the notch printed on the PC board. This stripe is clearly visible in the photo. Note that, because the
lettering on the op amp is upside down, the
op amp appears to be mounted upside down on the pc board. The op amp in the photo is, in fact,
mounted properly. It may be necessary to
gently straighten the op amp pins so they will fit in the holes. Make sure that all eight pins
are in their respective holes AND THAT THE
OP AMP IS PROPERLY ORIENTED! Solder all pins. In order to avoid overheating the op amp,
wait a few seconds between each pin.
7. Solder the green LED at component position D1 and the red LED at D2. The small flat place on the shoulder of the LED housing must match
the flat side of the drawing on the front of the PC board. Note that the flat place on the green LED faces "up" on
the pc board and the flat place on the red LED faces "down." MAKE SURE YOU HAVE PROPERLY ORIENTED THE LEDs BEFORE
YOU SOLDER THEM! IMPROPERLY ORIENTED LEDs ARE THE MOST COMMON CONSTRUCTION MISTAKE. It is very easy to
overheat these LED connections. Make sure your soldering iron tip is clean. Try to minimize the time during which
the iron is
in contact with the LED pins and PC board connectors. Make sure the LED housing fits flat against the front surface
of the PC board. This is much easier to do with two people -- one to press the LED against the surface of the board
and the other to solder the pins. After soldering one pin (it doesn’t make any difference which one you do first),
check to make sure that the LED housing fits flat against the front of the board. If it does not, reheat the
connection and gently push the housing down against the board. Wait at least 15 seconds between soldering the first
and second pins. Trim the excess leads from the back of the board.
8. Insert the two battery connector wires through the hole from the back
of the board. Tie a single loop knot about 3 cm
from the end of the wires. (See the photo.)
9. Solder the black wire from the battery connector to a -9V BAT connection point on the PC board. There is a line of 5
possible connection points for -9V. In the photo, the black wire is attached to the leftmost of these 5 connection
points.
10. Cut and strip a 3 cm (1-1/4") piece of red wire. Make a hook in one end of the wire and connect it to the center
terminal of the remaining SPDT switch. Solder the other end of the wire to a +9V BAT connection point. There is a line of 4
possible connection points for +9V. In the photo, the red wire is attached to the topmost of these 4 connection points.
11. Make a hook in the end of the red wire from the battery connector and solder it to an outer terminal of the
switch.
12. Cut a 4 cm (1.5") piece of black wire. Strip 1 cm of insulation from one end and 7 mm from the other end. Solder
the end with 7 mm of insulation stripped off to the COM connection point at the righthand side of the PC board.
13. Solder the green wire from the channel select switch to the OUT 1
connection point. Solder the outer red wire to the OUT 2
connection point.
This completes the wiring of the pc board for the GLOBE two-channel
sun photometer. The photo at the right shows the back of the completed pc board. Note that all leads are trimmed
close to the board. The solder connections are clean and shiny, with
no large "blobs" of solder or "crud" from a dirty soldering iron tip on any of the connections.
As noted at the beginning of these instructions, there are many
connection points on the pc board that are not used for this particular instrument.
C. Connect the battery and test the sun photometer.
It is helpful to complete the connections in the
order given so that you can test the operation of the instrument
before mounting it in its case.
1. Make sure the on/off switch is off -- when the switch toggle "points" toward the unused terminal of the switch,
the switch is in the off position. In the above photo of the completed pc board, the on/off switch is in the
on
position. Install the 9V battery in its clip by pushing the clip firmly down on the battery
terminals. Note that the terminals are different so the battery will connect only one way.
2. At this point, you can test the entire circuit. This is easier to do with two people. Read through all these
instructions first so you will know what to look for. Throughout this test, you must make sure that the bare ends of
wires from the switches and PC board do not touch each other anywhere.
For testing and using your sun photometer, use a
digital voltmeter (dvm) rather than an analog meter. Be
sure to select a DC volts setting. Some dvms are "autoranging," which means they will select an appropriate DC
volts range when a signal is applied to the test leads. In other cases, you must manually select a range. Typical
ranges are 200mV, 2V, and 20V.
When a dvm is connected to the output of
your sun
photometer with the battery switch off, you will see "junk"
readings on the voltmeter, but not the 0V you might expect. This is normal behavior for dvms. If you do not see the
voltages indicated below when the on/off switch is on, your sun photometer is not working.
To test the circuit, hold the
voltmeter leads against the output leads from the circuit board.
The positive (red) lead from the voltmeter should contact the red wire coming from the center terminal of the channel
select switch and the negative (black) lead should contact the black lead from the COM connection. In the photo,
a hook has been bent in the end of each output wire so that they will make good contact with the dvm leads. These hooks
will be needed later, too, when you complete the final assembly of your sun photometer.
Turn the on/off switch on. Depending on how well you can shield the LEDs from light,
your dvm should show a voltage of no more than a few millivolts. With the LEDs exposed to sunlight, test both channels by
changing the position of the channel
select switch. (It doesn't matter which channel you test first.) You should see an output of at least a few hundred
millivolts. In the photo, the dvm shows an output of about 202 mV for the red channel.
This test was made on a cloudy day. This wouldn't be an acceptable
condition for making a real measurement, but it is OK for testing the circuit.
If you have made a mistake in wiring the PC board, you will not see appropriate
voltages at the output. Such mistakes can include a short circuit somewhere on the PC board. This can cause the battery
to get warm, or even hot, to the touch. This is serious and you must find the source of the problem before proceeding.
Probably you will need to replace the battery, too.
3. When you're done, be sure to turn off both the sun photometer and your digital
voltmeter.
If your circuit passes this test for both channels, you are ready
to install the PC board, battery,
and switches in the case. It is unlikely that your sun photometer will not work if you have been careful with
construction. The components used to construct this instrument are very reliable and I have personally NEVER
had a properly constructed sun photometer fail to work. However, the emphasis is on "properly constructed."
If your
sun photometer doesn't work, it is almost surely due to an error on your part. Check your work, especially the
polarity of the LEDs and op amp and,
using a magnifying glass, the quality of the solder connections.
As you will find if you have to try it, it is very difficult to remove and
reinstall improperly connected
components. The copper traces on this PC board are delicate and it is easy to destroy the traces in the process
of removing and reinstalling components. For all practical purposes,
the op amp cannot be removed once it is soldered in place unless you have equipment specifically designed for
desoldering delicate electronic components. If not, you are better off starting over. With a great deal of
care, it is possible to reinstall the other components.
D. Install the PC board and battery in the case.
NOTE: In newer versions of the sun photometer kit, holes
for the pin jacks are in a line parallel to the top of the case, rather
than perpendicular to the top of the case. In this case, modify Step 1 to
include installing both the black and red pin jacks. The black pin
jack should go in the hole closer to where the PC board will go.
Later, when you get to Step 10, you can ignore the instruction to
install the red pin jack.
1. Install the black pin jack in the case. The black jack goes closer to the bottom of the case.
The black plastic ring goes on from the inside of the case, with the small "shoulder" fitting into the 7 mm (1/4")
mounting hole. Slide the lock washer over the threaded end, and then screw on the nut. Tighten the nut with pliers.
Make sure it is tight, as it is hard to reach this nut after the assembly is completed. The red pin jack will be
installed later.
2. Attach the alignment brackets with the sheet metal screws. The part of bracket that sticks up from the case goes
at each end of the case. Place a straight edge (like a ruler) on the case along the side of the brackets to make
sure they are straight. Tighten the screws, making sure that the bracket alignment doesn't change. Place a small drop
of superglue on each side of each bracket where it sits on the case. Be careful not to let this glue get on your fingers
or clothing, as it is impossible to remove and can irritate your skin. Let the glue dry for several minutes. Put a
piece of sticky-back paper over the front of the rear bracket (opposite from the end with the sun aperture), press it firmly
in place, and trim it neatly around the edges of the bracket with a sharp knife. (You can cut this piece of
paper from one side of the GLOBE Sun Photometer label.)
You can use two-part epoxy in place of, or in addition to, the superglue to attach
the brackets to the top of the case.
3. Remove the backing from the GLOBE Sun Photometer label and press it in place on the front of the case so that the on/off and grn/red text will
be aligned with the holes. (Hold the case up to a strong light to help with the alignment. Using a craft knife, cut out
the label over the holes.
4. Remove one nut and both washers from both toggle switches. Discard the larger flat washers, but keep the small
toothed lock washers. On each switch screw the remaining nut down to the end of the bushing against the switch housing.
Tighten it gently. (It is sufficient just to use your fingers for this.)
5. Gently twist the on/off switch so that the unused terminal is facing away from the PC board.
Gently twist the channel select switch so that the terminal with the green wire is facing toward
the PC board.
6. Slide the PC board into the slot nearest the end with the toggle switch holes. The front side of the board should,
of course, face toward the end of the case with the sun aperture hole in it. The battery clip fits in the space
behind the PC board. Guide the two toggle switches into their holes. Use needle nose
pliers to gently bend wires as needed so that the toggle switches fit into their holes. Try not to bend a wire
where it connects to the PC board, as this is where the wire is mostly likely to break because of a nick that you
may have made when you were stripping it. If a wire breaks, unsolder the broken end from the PC board, restrip the
wire, and resolder it. (The original lengths specified for the wires are long enough to allow you to do this.) When
you are done with this step, the PC board should rest on the bottom of the case and the switches should be in their
holes oriented as noted in the previous step. Make sure no wires are near the LEDs, where they could block sunlight
shining on the ends of the LEDs.
7. Make sure the on/off switch is in the "off" position. Snap the 9V battery into its connector.
Hold the piece of foam plastic against the back of the PC board and push the battery into place,
between the end of the case and the foam plastic. Be sure that the foam plastic is between the battery and the back of the PC board.
8. From the outside of the case, slip the lock washer and nut over the protruding threaded bushing of the on/off
switch and screw the nut on. Tighten this nut with pliers. Do the same with the channel select switch. It
easy to strip the threads of these small nuts. If that happens, you can switch this nut with the one currently
screwed down against the switch housing and try again. Be careful not to put pressure on the toggle with the pliers
while you tighten the nuts, as it is easily broken.
9. Using needle nose pliers, make a loop in the end of the black wire coming from the COM connector on the PC
board. (You may already have made this loop when you tested your circuit in sunlight.) Wrap this loop around the end
of the black pin jack and solder it in place. This connection requires much
more heat than connections made on the PC board and it is important to heat the pin jack sufficiently that solder
flows around the wire and the jack terminal. I have found a 15-watt soldering iron insufficient to make a secure
connection to the pin jacks.
10. Install the red pin jack in the remaining hole. Make a loop in the end of the red wire coming from the center terminal
on the channel select switch and solder it to the red pin jack. When you finish this step, make sure that wires do not
touch adjacent terminals on the channel select switch. Check to see that the nuts on the on/off and channel select
switches are tightened from the outside of the case. It is important for the switches to be aligned as shown in the photo.
Make sure that the black pin jack does not touch any terminal of the channel select switch.
NOTE: As you should know from reading the protocols, it is important to try to keep your sun photometer as close to
room temperature as possible (around 20°C) when you are making measurements, because the output varies a little with
temperature. This problem cannot be solved completely except by actively
controlling the temperature of the electronics -- a solution that is much too expensive for this GLOBE instrument.
It is possible, however, to employ simple passive techniques.
I have made
an outer case of 1-cm thick rigid plastic foam (Styrofoam) with cutouts
for switches, etc., held together with aluminum tape.
This is especially useful in the summer, as the white styrofoam is an excellent reflector and insulator.
E. Test your completed sun photometer in sunlight. Do this with the case cover off.
1. Plug your digital voltmeter into the output jacks. Select a DC volts
setting. If the range must be manually set, use a range that will measure
up to 2V.
2. Take your sun photometer outside and turn the on/off switch on. Position the open side of the case so sunlight
falls on the detectors. Your voltmeter should read somewhere between 0.5 V and 2 V in full sunlight. Test both
channels. It is possible that the output voltage for one or both channels in full sun will exceed 2V. This is OK,
but you may need to choose a different DC volts scale on a dvm that is not autoranging.
If if it not possible to test your sun photometer in sunlight, it should respond
even to bright artificial lights. In my own shop, sun photometers typically read a few tens of millivolts when I
hold the detectors close to a double-tube fluorescent fixture.
F. Complete the assembly of your sun photometer.
1. Make sure there is no dust or debris inside the case. Gently clean the ends of the LEDs with the corner of a
damp paper towel. After doing this, do not touch the ends of the LEDs with your fingers.
2. Determine which way the cover fits best -- usually one orientation lines up with the sides of the
case a little better. Fasten the adhesive foam plastic strip on the
inside of the cover so that it will press down on the edge of the circuit board when the cover is fastened
to the case. (The purpose of this strip is to keep the circuit board in place, pushed against the bottom of
the case.)
3. Attach the cover with the four self-tapping Phillips head screws.
4. Follow the alignment procedure described elsewhere on this web page.
Your GLOBE sun photometer is now ready to use. Note that there is space for a serial
number on the label.
Your sun photometer must have a serial number before you can enter measurements through the GLOBE web site. Serial numbers
are assigned only to instruments that have been calibrated by or in consultation with the Science Team.
Parts Included With Kit
Be careful not to lose any parts, as no duplicate or extra parts are provided.
One GLOBE sun photometer case, predrilled, with screws for cover
One GLOBE sun photometer printed circuit board, Version 3.0
One 2.2 MOhm, 1/4W, 5% carbon film resistor (color coded red-red-green-gold, or some other value)
One 5.6 MOhm, 1/4W, 5% carbon film resistor (color coded green-blue-green-gold, or some other value)
One 0.1 uF ceramic disc capacitor
Two 220 pF polystyrene or ceramic disc capacitors
One LT1051CN8 op amp
One red LED (modified by GLOBE Science Team)
One green LED (modified by GLOBE Science Team)
Two SPDT miniature toggle switches with hardware
One 9V battery
One snap-on battery connector
One red pin jack with hardware
One black pin jack with hardware
Two #6x1/4" sheet metal screws
6" #22 red wire
6" #22 black wire
2" #22 green wire
Two L brackets (corner irons)
One self-adhesive label
One square of foam plastic
Two colored alignment dots (red and green)
Small piece of blank adhesive label (for rear alignment bracket)