Ramsey Electronics PM10DC User manual

Ramsey Electronics Model No. PM10DC
Ever need to tune up RF equipment, but didn’t have the money
for expensive watt meters and spectrum analyzers? Want to be
able to measure low-level signals and high-level signals without
changing slugs and flipping switches? This versatile piece of
test equipment should be standard on every RF experimenter’s
bench. Hundreds of uses!
•Accurately tune and match your antenna for maximum
performance!
•Can accurately measure signals from –29dBm to +47dBm; that’s
<2 microwatts to 50 Watts!
•Auto-scaling display shows forward power and reverse power in
dBm, watts, peak power, and average power! Also displays
percent of AM modulation!
•2x8 Line LCD display shows measurements on a clear and easy to
read display!
•Runs from 7-15V AC or DC. Use our AC-1 wall adapter.
•Highly accurate (+/-1dB) from 2MHz to 450MHz. Effective from
100kHz to 1GHz, however refer to the sensitivity charts in the
manual for conversions and limitations.
•Perfect match for tuning and testing our various transmitters such
as the FM100, FM25, PX1, TX433, AM1, AM25, and the QRP line of
transmitters. Tune your product for maximum efficiency!
•See transmission levels down where other meters simply cannot
go!

PM10DC y2
RAMSEY TRANSMITTER KITS
• FM100B Professional FM Stereo Transmitter
• FM25B Synthesized Stereo FM Transmitter
• MR6 Model Rocket Tracking Transmitter
• TV6 Television Transmitter
RAMSEY RECEIVER KITS
• FR1 FM Broadcast Receiver
• AR1 Aircraft Band Receiver
• SR2 Shortwave Receiver
• SC1 Shortwave Converter
RAMSEY HOBBY KITS
• SG7 Personal Speed Radar
• SS70A Speech Scrambler
• BS1 “Bullshooter” Digital Voice Storage Unit
• AVS10 Automatic Sequential Video Switcher
• WCT20 Cable Wizard Cable Tracer
• LABC1 Lead Acid Battery Charger
• LC1 Inductance-Capacitance Meter
RAMSEY AMATEUR RADIO KITS
• DDF1 Doppler Direction Finder
• HR Series HF All Mode Receivers
• QRP Series HF CW Transmitters
• CW7 CW Keyer
• CPO3 Code Practice Oscillator
• QRP Power Amplifiers
RAMSEY MINI-KITS
Many other kits are available for hobby, school, Scouts and just plain FUN. New
kits are always under development. Write or call for our free Ramsey catalog.
PM10DC DIRECTIONAL COUPLER POWER METER KIT MANUAL
Ramsey Electronics publication No. MPM10DC Revision 1.3a
First printing: July 2002 MRW
COPYRIGHT 2002 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.

PM10DC y3
PM10DC ADVANCED DIRECTIONAL
RF POWER METER
Ramsey Publication No. M PM10DC
Price $5.00
TABLE OF CONTENTS
Introduction ...........................................4
Theory of Operation ..............................5
Learn As You Build ...............................8
Parts List .............................................12
Assembly (Display) .............................14
Assembly (Main Board).......................16
Schematic Centerfold..........................18
Directional Coupler Assembly.............22
Front and Main Board Mounting..........26
Testing.................................................27
Using the PM10DC .............................30
How to Tune an Antenna ..............31-33
Board Layouts, Schematic .............34-35
Troubleshooting ..................................36
Sensitivity vs. Frequency Chart...........37
Pictures ...............................................38
Warranty..............................................39
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR

PM10DC y4
PM10DC INTRODUCTION
Welcome to the PM10DC kit (and if you don’t have the time, the wired and
tested version). This is a product that many of you were asking for; a powerful
bench-top power meter in our standard kit case. It is based around two AD8307
log detectors which have a 90dB dynamic range for signal strength
measurements. Tie that to a good directional coupler and you have yourself a
very easy to build and calibrate power meter! Since the AD8307s respond very
quickly to changes in signal level they are also perfect for deriving percent of
modulation, peak power, average power and more!
The real advantage to this power meter is its ability to measure very small
signals from low-power transmitters such as the FM10a, and even smaller. This
allows you to accurately tune the last stages of a transmitter’s filter or gain
stages for maximum efficiency and transmission range. Because it also has a
directional coupler, you can also check the match of your antenna by looking at
the VSWR reading as well as reflected power. The less reflected power, the
more power being transmitted over the air. Without this power meter, you might
simply have to go with your best guess!
Since this unit also contains a directional coupler you can not only measure
forward power (power which exits the generating device), but you can also
measure reverse power (power which returns into the generating device). The
measure of how good a directional coupler is is called directivity. Directivity is
defined in dB and tells us how much dB difference there is between forward
power measurements and reverse power measurements into a perfect 50 ohm
load. While this directional coupler does not cover the entire operating range of
the forward power meter, it has at least 20dB of directivity from 1MHz to
200MHz, and has 37dB of directivity at 50MHz, which is a factor of 5000 to 1.
We hope you enjoy building this kit since we had a lot of fun designing it for
you. To keep costs down, we have miniaturized the kit to fit in our standard
plastic case and panels. This is arguably one of the neater kits we have
developed!

PM10DC y5
PM10DC THEORY OF OPERATION
If we’ve done our job you will come away from this theory with a greater un-
derstanding of electronics, dBm, and how power is measured from transmit-
ters. You may also learn why this power meter has such fantastic range, and
you’ll find out why our engineer (me) has such a bad headache after writing
routines to convert an analog to digital value to dBm and then to watts, and
then to VSWR using nothing but assembly language on an 8-bit processor!
The C language equivalent just wouldn’t fit in such a small microcontroller.
The heart of the power meter is the broadband directional coupler. There are
several possible directional coupler designs, but the one we chose is the most
broadband, but also rather difficult to hand assemble. We figured you could
tackle this because it’s worth the trouble in the end.
Refer to figure 1: A directional coupler works
by having two cross-coupled transformers
that either cancel each other’s signal out, or
not, depending on the direction of power. It is
tricky to describe this in easy to understand
terms, but I will summarize by saying that
when power is going from port B to port A,
some small portion of power will be also be
on port C. The amount of power seen on port
C is determined by the ratio of the number of
windings, shown here as 7:1. Power coming
back flows from A to B, which causes a small
portion to be seen on D. If there is equal
power going in both the forward and reverse directions there should be less
power at D and C. The power is sampled on D and C, and this is done with
the AD8307 log detectors. VSWR is calculated from the ratio of the power be-
tween C and D.
The AD8307 IC used on each side of the directional coupler is pretty fantas-
tic. This IC has a range of roughly –80dBm to +12dBm. This translates to a
range of 92dB! This is simply amazing since it converts this range to a linear
dB to volts output, which can then be sampled by an analog to digital con-
verter. Since 10 Watts translates to +40dBm, we see that this little part would
be overwhelmed by such a high signal. So to remedy this, we make sure we
have 30dB of attenuation between the directional coupler and the AD8307.
Part of the attenuation is performed by the turns ratio, the other part is from a
small “pad” consisting of R12, R8, and R1 on the forward power side. This
means +40dBm becomes +10dBm, and –40dBm becomes –70dBm.
The AD8307 outputs 25mV per dB of signal so if we run this signal into an A/
D converter we can convert this 25mV/dB into a usable number for further cal-
culations. In our case we are using a 12-bit A/D converter to maximize resolu-
Power
In Power
Out
Forward
Out
Reverse
Out
GND
figure 1

PM10DC y6
tion and accuracy. For our dB range of the detector (-40dBm to +40dBm) this
comes out to an output voltage range between 0.4V to 2.5V. Now if we have
the converter set up to convert between 0-2.5V, this means we have a poten-
tial accuracy of 2.5 / numSteps or 2.5 / 2^12 or 610uV per step, or in other
words 610uV / 25mV/dB = .024dB per step. A fair bit of resolution to start
with!
Before going directly to the analog to digital converter however, we do some
signal conditioning on the output of the AD8307s with U1:A and U1:B, which is
a non-inverting amplifier and low-pass filter. The low-pass filter helps to re-
move noise and higher frequency changes in power level, like very fast AM
signals, to give us a better average dBm reading. DC-wise this has a gain of
1+Rf/Ri or 1+10K/1K or 1.1. This means our 25mV per dB now becomes
27.5mV per dB. We simply adjust the code to scale the numbers differently to
get the correct results on the display.
U4 is an amazing little part, with accurate timers, a 10-channel 8-bit analog
to digital converter, all sorts of interrupts and more; there is a heck of a lot you
can do with this tiny part! In our case we are mostly doing math on the sam-
pled results of the AD8307s, and the rest is user interface stuff like looking at
the switch and updating the display. When the average power mode is se-
lected, we can take upwards of 100 dB results, convert it to power, add the
power to a total sum, then take the average of all of them and display it all
within one second’s time. All this while maintaining math accuracy of +/-
0.024dB!
So, how is the math done, you may ask? Well, there isn’t enough room to go
into detail but here are some basic formulas I used to get this to happen.
Since our A/D converter is measuring at 27.5mV per dB, and our reference
is 2.5V, it just so happens that the math works out to taking the conversion
value (0-4095) and multiplying it by 27.5 which gives us a result in dB * 1024.
1024 is a power of two, meaning that if we do some more shifting to the right
(essentially a single bit shift to the right divides by two) we can get the correct
value in dB. Let’s say our sample is 1000; we multiply by 27.5 so the answer
is 27500. This is now dB * 1024, so let’s bit shift the answer to the right 10
times, which divides by 1024. The answer becomes 26.86dB! Now we only
have to factor in the attenuation, and in the case of how we calibrate the
PM10DC and the attenuation, we need to subtract 48.6dB from this answer to
get actual dB. This comes out to the conversion of 1000 = -21.74dBm!
Now that we have our dBm result we have to calculate watts from it when we
need to display watts. This gets a bit tricky since we are talking about loga-
rithms. To the left is the formula which converts dBm to
power. This is implemented in the microcontroller in a
lookup table and some interpolation to get high speed
and high accuracy. Let’s just plug the numbers in and
Pdb()10
db
10 0.001
.

PM10DC y7
see what we get:
As you can see the result is in scientific, but if we look
close, we see the result is 6.7 micro watts! A pretty small
value to be sure.
Now if we need to display VSWR, we need to use the follow-
ing formula. This will give use the ratio of reflected power to
absolute power. The problem here is we need to convert
both forward and reverse powers to watts, divide the reverse
power by the forward power, take the square root of the re-
sult, find 1—answer and 1 + answer and divide those also. It
is a bit of a daunting task, and square roots are a bit tricky in
a small micro-controller when you have to write
your own math routines. Imagine doing this by hand
2 times a second!
Since this is an advanced meter, we not only
wanted to display peak power, but also average
power. Average power cannot be calculated by
simply summing all of the dBm readings and taking the average; you cannot
average power by averaging dBm! For example let’s say we have two read-
ings of 0dBm and –20dBm. The average dBm would be –10dBm, which is 0.1
miliwatts but the average watts is actually 0.5 miliwatts. Quite a difference,
and this is with only two samples. Imagine how far off we would be after 200
all averaged together. So to take average power, we need to convert the dBm
from the samples to watts each time, sum the watts, then take the average
watts, not dBm. This slows things down a bit, but at least the accuracy is
there. Luckily the processor is fast enough to average 100 samples before up-
dating the display, giving you a pretty good idea of average power.
Another useful thing the PM10DC does is show percent of AM. Since we
can take more than 200 samples between screen updates, we can take all of
the samples and look for the maximum level and the minimum level. Then
when we calculate the difference between the two, we can derive the percent
of AM modulation! Rather than do some really fancy math to find AM, we
cheat and use a lookup table. It is much faster and it can compensate for
slight error in the AD8307s not responding fast enough to high-frequency AM.
We wind up with an accuracy of +/-1% of AM, which is not bad at all! Since we
only look at the difference in level from peak to valley of the reading, the AM
modulation readings are good from 100kHz up to 1GHz, even though the ac-
curacy of the power meter falls off after 450MHz.
Well, if your eyes aren’t glazed over I hope you have learned something
from this; the math is a real challenge! Imagine doing all of this math on a little
calculator with just Add, Subtract, Divide, and Multiply. Now you begin to un-
derstand, grasshopper, why you are getting a LOT for your money!
Pdb()10
db
10 0.001
.
P 21.74( ) 6.7 10 6
.
=
VSWR
1
Pr
Pf
1
Pr
Pf
P020
2
1104
.
=
P0() P 20
()
2
5.05 10 4
.
=

PM10DC y8
RAMSEY “LEARN-AS-YOU-BUILD” ASSEMBLY STRATEGY
Be sure to read through all of the steps, and check the boxes as you go to be
sure you didn't miss any steps. Although you may be in a hurry to see results,
before you switch on the power check all wiring and capacitors for proper
orientation. Also check the board for any possible solder shorts and/or cold
solder joints. All of these mistakes could have detrimental effects on your kit -
not to mention your ego!
Through-hole part installation:
Use a good soldering technique - let your soldering iron tip gently heat the
traces to which you are soldering, heating both wires and pads simultaneously.
Apply the solder to the iron and the pad when the pad is hot enough to melt the
solder. The finished joint should look like a drop of water on paper, somewhat
soaked in.
Mount all electrical parts on the top side of the board provided. The top side is
clearly marked with the word “TOP”; you can’t miss it. When parts are installed
each part is placed flat to the board and the leads are bent on the backside of
the board to keep the part from falling out before soldering (1). The part is then
soldered securely to the board (2-4), and the remaining lead length is clipped
off (5). Notice how the solder joint looks on close up, clean and smooth with no
holes or sharp points (6).
Since this is a “professional” piece of test equipment, we sincerely hope you
put this together in a professional manner. Follow good assembly techniques,
and follow all instructions. No matter how clear we may think our manual is, if
you have any questions give us a call at the factory instead of jumping to
conclusions, we will be happy to help you with any problems.
This is a mixed signal project meaning there is digital and RF circuitry all in
one unit. As with all RF circuitry, we want to mount the parts AS LOW AS
POSSIBLE to the board. A 1/4” lead length on a resistor not mounted close to

PM10DC y9
the board can act as an inductor or an antenna, causing all sorts of problems in
your circuit. Be aware though that there are stand up components in your
circuit. They don’t need to be squished to the board, but keep the portion of the
resistor closest to the board mounted right on the board.
For each through-hole part, our word "Install" always means these steps:
1. Pick the correct part value to start with.
2. Insert it into the correct PC board location, making sure the part is
mounted flush to the PC board unless otherwise noted.
3. Orient it correctly, follow the PC board drawing and the written directions
for all parts - especially when there's a right way and a wrong way to solder
them in. (Diode bands, electrolytic capacitor polarity, transistor shapes,
dotted or notched ends of IC's, and so forth.)
4. Solder all connections unless directed otherwise. Use enough heat and
solder flow for clean, shiny, completed connections.
Surface Mount part installation:
Check all received parts against the Parts list. The parts list describes the
various markings that may be found on the kit parts.
In the case of a surface mount component, INSTALL means these steps:
•Dab a small amount of solder on one pad on the PC board of the
component you wish to install. Usually choose pin 1 of ICs.

PM10DC y10
•Locate the part from one of the bags.
•Use tweezers to pick up the part, grabbing it across the body of the part,
not the solder connections.
•Place the part in the assembly location. Use one hand to hold the
tweezers and part in place.
•Use the other hand to re-heat the solder dab to melt it to the component
connection.
•Let the solder cool and let go with the tweezers. Inspect orientation and
make sure the part is square and oriented over the correct pads. Also
make sure a connection doesn’t overlap or short across adjacent pads
and the part is placed flat on the PC board.
•Apply solder to the rest of the pads.
•Apply a touch more solder to the initial pad if needed to make sure there is
a good solder joint.

PM10DC y11
NOTE TO NEWCOMERS: If you are a first time kit builder you may find this
manual easier to understand than you may have expected. Each part in the kit
is checked off as you go, while a detailed description of each part is given. If
you follow each step in the manual in order and practice good soldering and kit
building skills, the kit is next to fail-safe. If a problem does occur, the manual
will lead you through step by step in the troubleshooting guide until you find the
problem and are able to correct it.
•If you have too much solder, and wish to remove it, user solder wick to
“mop up” the extra solder. Solder bridges on SMT IC pins are a frequent
occurrence so you should always have some solder wick handy.
Enough said. . . Let's get building!
You are going to want to use a VERY clean desk space to assemble the
surface mount parts of your kit. Drop a resistor into even the smallest amount
of clutter, and it will disappear like magic, in fact you would swear a magician
was hovering over your shoulder in some cases when part after part
disappears. There are probably enough parts hidden in the papers on my
desk to hide an entire communications system, but we wont go there.
Use only one surface mount part at a time, don’t pour them out all over the
desk, only retrieve a single component (I wet my finger a bit to have a part
stick to it), place the part on the desk, and then pick it up with the tweezers.
This lets me orient the part so the markings are on the top. It also provides me
with Tiddly Winks practice; *Ping* and I hear the part bounce off of the other
wall, and down into the heat register. If you are really careful, this won’t
happen.

PM10DC y12
RAMSEY PM10DC PARTS LIST
Supplies
1 1N4002 Rectifier Diode (Black body with white stripe marked 4002)
(D1)
1 78L05 Voltage Regulator (TO-92 Case) (VR1)
1 ADS7841PBN 12-Bit 4-channel A2D converter (U2)
1 LMC662 Dual Rail to Rail opamp (U1)
1 Pre-programmed MC68HRC908JK3 (U4)
8 0.01uF ceramic capacitors (Marked 103) (C1,3,4,6,7,15,25,26)
4 0.1uF ceramic capacitors (Marked 104) (C2,10,11,18)
1 10pF ceramic capacitor (Marked 10 or 10K) (C16)
4 10uF electrolytic capacitors (C5,8,19,23)
1 1000uF electrolytic capacitor (C24)
1 3.9uH inductor (orange-white-gold) (L1)
2 1K ohm resistors (brown-black-red) (R20,21)
1 10K ohm potentiometer (Orange top, 103) (R4)
2 50K ohm potentiometer (Orange top, 503) (R13,19)
1 47K ohm resistor (yellow-violet-orange) (R11)
2 100K ohm resistors (brown-black-yellow) (R14,18)
2 1.0K ohm 1% resistors (brown-black-black-brown) (R1,3)
1 2.0K ohm 1% resistor (red-black-black-brown) (R9)
3 10.0K ohm 1% resistors (brown-black-black-red) (R2,5,6)
1 13.0K ohm 1% resistor (brown-orange-black-red) (R7)
2 8-Pin dual row header (Or one 16-pin cut in half) (J2,6)
1 14-Pin dual row header (goes with display) (DS1)
1 20-Pin IC socket.
1 2x8 Line Optrex LCD display (DS1)
1 DPDT pushbutton switch (S3)
2 SPST pushbutton switches, long neck (S1,S2)
2 BNC board mounted connectors (J3,4)
1 2.1mm Power Jack (J7)
1 Binocular Core, type: (DC1)
48” Of #24 magnetic wire.
6” #16 Bus Wire
1 50 Ohm terminator.

PM10DC y13
Surface Mount
2 AD8307AR Log detectors (U3,5)
2 0.001uF ceramic SMT capacitors (C13,21)
4 0.01uF ceramic SMT capacitors (C12,14,20,22)
2 0.1uF ceramic SMT capacitors (C9,17)
2 33 Ohm SMT resistors (Marked 330) (R10,17)
2 75 Ohm SMT resistors (Marked 750) (R12,16)
2 120 Ohm SMT resistors (Marked 121) (R8,15)
2 1K Ohm SMT resistors (Marked 102) (R22,24)
2 47K Ohm SMT resistors (Marked 473) (R23,25)
Note: 1% resistors read a bit differently than 5% resistors. For example a 10K
ohm resistor in the 5% method would be Brown for 1, black for 0, orange for 3
places after the last defined digit, and then gold to identify the part as a 5%
component. So 1-0-000 ohms +-5%.
A 1% 10.0K resistor needs to identify one more place of precision than a 5%
resistor does, so it includes an extra stripe. In this case it would be brown for
1, black for 0, another black for another 0, red for two remaining zeros, and a
brown to indicate 1%. So 1-0-0-00 +-1%. It is easy to mix up what end is what
on these resistors, because either end begins with brown. Typically the preci-
sion stripe (which is always last) is wider than the rest, kind of like a period. So
always start from the end with the narrow stripe.

PM10DC y14
ASSEMBLY (DISPLAY)
Assembly of your PM10DC is fairly straightforward, and surprisingly simple
for a complex kit. We will assemble things in three different sections to keep
things simple. Note, however, that the drawings show all of the parts on the
top of the board. THIS IS NOT THE CASE! Headers J2 and J6 are mounted
on the back of the board. Follow the directions closely and we will get this
working right the first time.
1. We will begin with the display board. If this has not been done for you
already you will need to break off the display board from the main board
along the line of holes or routed notch. If necessary place the line of holes
along the edge of a table top and press down on the board to snap it off.
Afterwards you may find that there’s a lot of material hanging off the edge;
this is fiberglass. Use a file to smooth the edges down so it isn’t sharp.
2. We need to install the 14-pin dual row header into the LCD display but
be careful not to install it on the wrong side! The header will be installed
on the back of the LCD display. Soldering will all be done on the front of
the display (which is the side that displays things), and we will be
soldering the short ends on the display board. Make sure all 14-pins are
soldered well. Hold the heat there for a bit with the soldering iron to make
sure the solder has flowed down into the drill holes.
3. On the top of the display there are two screw hole tabs. These will get
in the way of mounting the PM10DC inside a case. We will need to cut
them off after bending them over flat toward the back of the display so
they don’t stick up. First bend over the tabs and then, using sharp
clippers, trim off the tabs so they don’t stick out further than the IC on the
back of the display board does.
4. Do not install yet. Locate J2 and J6, the 8-pin dual row headers. If you
only have a 16-pin header you will need to cut this in half to make two 8-
pin dual row headers. These headers will be used to mount and position
the display board to the main board, as well as run signals between the
two boards. These two jacks need to be soldered nice and square to the

PM10DC y15
board to make sure the display will mount properly in the case, so only
solder one lead and then check positioning.
5. Install J2 ON THE BACK of the board, which is clearly marked. Solder all
eight pins.
6. Install J6 ON THE BACK of the board. Solder all eight pins. All parts from
this point on will be installed on the front of the board.
7. Install R18, one of the 100K ohm resistors (brown-black-yellow).
8. Install R14, another 100K ohm resistor (brown-black-yellow).
9. Install R4, the 10K ohm potentiometer (orange top marked 103). This will
be used to adjust the display contrast. If you see nothing on the display
later when we get to the testing phase you’ll probably need to adjust this.
10. Install C10, a 0.1uF ceramic capacitor (Marked 104). This capacitor
keeps any noise that the display may be generating away from the rest of
the circuitry.
11. Install C7, a 0.01uF ceramic capacitor.
12. Install S1, one of the momentary pushbutton switches. Make sure it is
flush and square to the board before soldering.
13. Install S2, the other momentary pushbutton switch. These two switches
will be used to toggle through the various modes of your power meter.
14. Install the display as shown. Make sure the display is mounted as flush
as possible to the board so that it will press up to the front panel of the case
and knob set properly. If it sits too far out, the display will push against the
front panel. Trim off the remaining leads of the long end of the connector
when finished.
You’ve now completed the display panel! We will eventually be attaching this
display panel to the main board but we will get to that later. If we attached it
now it would be very difficult to install parts on the main board later, especially
the power switch. On the next page we will begin working on the main board.

PM10DC y16
ASSEMBLY (MAIN BOARD)
We are now going to build the main board. We will refer to the parts
placement page in the later part of this manual for placement. This is where
the brains and the brawn of the project are. It contains the microcontroller (U4)
and the 12-bit analog to digital converter, as well as some signal conditioning.
We will begin at the front of the PCB and work towards the back. Note that J1
and J5, which are indicated on the board, are actually J6 and J2 respectively,
so you don’t need additional headers for these parts. They are installed when
we mount the display panel to the main board later.
1. Install C11, a 0.1uF ceramic capacitor (Marked 104).
2. Install C26, a 0.01uF ceramic capacitor (Marked 103).
3. Install R21, a 1K ohm resistor (brown-black-red).
4. Install R9, a 2.0K ohm 1% resistor (red-black-black-brown).
5. Install R7, a 13.0K ohm 1% resistor (brown-orange-black-red).
6. Install C6, a 0.01uF ceramic capacitor (Marked 103).
7. Install R5, a 10.0K ohm 1% resistor (brown-black-black-red).
8. Install C5, a 10uF electrolytic capacitor. Note that electrolytic capacitors
are sensitive to polarity; they are only properly installed in one direction!
The capacitors typically have a stripe indicating the negative side (-), and
we indicate the positive side on the board (+). Make sure to mount the
negative side of all electrolytic capacitors away from the positive symbol
indicated on our boards.
9. Install C2, a 0.1uF ceramic capacitor (Marked 104).
10. Install R2, a 10.0K ohm 1% resistor (brown-black-black-red).
11. Install C1, a 0.01uF ceramic capacitor (Marked 103).
12. Install R1, a 1.0K ohm 1% resistor (brown-black-black-brown).
13. Install R3, a 1.0K ohm 1% resistor (brown-black-black-brown).
14. Install C4, a 0.01uF ceramic capacitor (Marked 103).
15. Install R6, a 10.0K ohm 1% resistor (brown-black-black-red).
16. Install R20, a 1K ohm resistor (brown-black-red).
17. Install C25, a 0.01uF ceramic capacitor (Marked 103).
18. Install C18, a 0.1uF ceramic capacitor (Marked 104).
19. Install R11, a 47K ohm resistor (yellow-violet-orange). Note this
resistor is installed in a stand-up position.

PM10DC y17
20. Install C16, a 10pF ceramic capacitor (Marked 10 or 10K).
21. Install C3, a 0.01uF ceramic capacitor (Marked 103).
22. Install L1, a 3.9uH inductor (orange-white-gold). This inductor keeps
any noise on the power supply out of the side of the circuit which contains
the AD8307. Any noise present on the ICs is detected and would give us
incorrect readings with low level signals if it were not blocked by the
inductor.
23. Install C19, a 10uF electrolytic capacitor. Again pay attention to
polarity.
24. Install U1, the LMC662 Dual Rail to Rail opamp. Make sure to align
the dimple or notch with the dimple as indicated on the parts layout
diagram. This indicates pin one of the device. Solder all 8 pins.
25. Install U2, the ADS7841PBN 12-Bit analog to digital converter. Make
absolutely sure you align pin one as shown! Solder all 16 pins.
26. Install the 20-Pin socket in place of U4; this will allow you to easily
replace U4 in case of any available code updates.
27. Install U4 in the previously installed socket. This is the
MC68HRC908JK3 (it may have a silver sticker). This is the micro-
controller, and therefore contains all of the intelligence of the kit. Make
sure pin 1 is aligned properly and that all 20 pins are lined up before
seating the IC into place.
28. Install C15, a 0.01uF ceramic capacitor (Marked 103).
29. Install VR1, the 78L05 voltage regulator. This part has the job of
making the supply voltage “flat” at 5.0V output with a number of varying
inputs.
30. Install C23, a 10uF electrolytic capacitor. Again check polarity.
31. Install D1, a 1N4002 type rectifier diode. This diode has the job of
converting AC power to DC power from your power supply and also
preventing you from accidentally applying the wrong polarity to the power
supply. This gives us pulsed DC, which C24 will smooth out for us.
32. Install C24, the 1000uF electrolytic capacitor. Pay very close attention
to polarity, since putting this big capacitor in backwards can be a large
problem.
Now we are going to install our surface mount components. Since it is really
easy to lose them we will want to put them in a small container or set of
containers like a cardboard egg carton. Plastic egg cartons will have too much
static since they are Styrofoam so don’t use those. Sort out all of your
components and note that we give you extra, because we know a few will fly

PM10DC y18

PM10DC y19

PM10DC y20
off and hide in the shag carpets. Ok, maybe not shag, but invariably they will
dive down into the smallest hole or under immobile furniture. Again refer to
assembly instructions for surface mount components in the start of this
booklet.
33. Install U3, one of the AD8307 ICs. Note how we indicate a dimple for
pin 1, but there are no dimples on the AD8307. That is because some
manufacturers think it is easier to identify part’s pin 1 by creating a
tapered edge on the part. Pin 1 is located on this tapered edge; line this
up with the side of the part that has a square to indicate pin 1 (as well as a
notch). Solder only one pin then you can reposition the part before
soldering the rest of the pins.
34. Install C13, a 0.001uF ceramic SMT capacitor.
35. Install C9, a 0.1uF ceramic SMT capacitor.
36. Install R24, a 1K ohm SMT resistor (Marked 102).
37. Install R25, a 47K ohm SMT resistor (Marked 473)
38. Install C14, a 0.01uF ceramic SMT capacitor.
39. Install R10, a 33 ohm SMT resistor (Marked 330).
40. Install R12, a 75 ohm SMT resistor (Marked 750).
41. Install R8, a 120 ohm SMT resistor (Marked 121).
42. Install C12, a 0.01uF ceramic SMT capacitor.
43. Install U5, the other AD8307 IC. Remember to only solder one pin and
check orientation before continuing.
44. Install C22, a 0.01uF ceramic SMT capacitor.
45. Install C20, a 0.01uF ceramic SMT capacitor.
46. Install R17, a 33 ohm SMT resistor (Marked 330).
47. Install R15, a 120 ohm SMT resistor (Marked 121).
48. Install R16, a 75 ohm SMT resistor (Marked 750).
49. Install C17, a 0.1uF ceramic SMT capacitor.
50. Install C21, a 0.001uF ceramic SMT capacitor.
51. Install R22, a 1K ohm SMT resistor (Marked 102).
52. Install R23, a 47K ohm SMT resistor (Marked 473).
53. Install R13, a 50K ohm potentiometer. (Orange top marked 503).
54. Install R19, another 50K ohm potentiometer. (Orange top marked
503).