ETEC474 - Western Washington University
SGPRS: Hardware
Description
Senior Project - 2013
Justin A. King
6/4/2013
Contents
PIR Sensor ..................................................................................................................................................... 2
Solar Powered Circuitry ................................................................................................................................ 3
3.3V Regulator .............................................................................................................................................. 4
6V regulator .................................................................................................................................................. 5
MSP430G2553 and Servo ............................................................................................................................. 6
Parts List ........................................................................................................................................................ 7
1
PIR Sensor
The above circuit provides the motion detection functionality of the SGPRS project. The PIR sensor,
XDCR1 is, as its symbol indicates, essentially a FET with a gate that is driven by two IR light sensing
elements. When the gate is tripped, the positive rail is attached to ground through a large resistor (R5 =
47k), and current flows through the rest of the circuitry. The response from XDCR1 is very small, so the
signal needs to be conditioned so that it can be useful. U6-A and U6-B and accompanying resistors and
capacitors provide enough gain (36dB) to boost the signal to an acceptable level. The signal is then
passed through a window comparator that is formed by U6-C and U6-D so that it will only output if the
signal is between 78% and 21% of Vcc (determined by the resistors R14, 12, and 13). When the signal
falls between these levels, the output is the 6V rail, minus the voltage drop across the diode (D3 or D2).
This output is used to drive the input of the MOSFET Q2, which connects the 3.3V rail to an input pin on
the MSP430G2553. The other resistors and capacitors that are spread throughout the circuit are used
for decoupling and removing ripples from the signal. The large resistor values and the MCP6044 make
the quiescent current for this module very low (in the µA range).
2
Solar Powered Circuitry
The above circuit provides solar charging capabilities for the battery that powers the SGPRS. XDCR2 is an
array of solar panels that generate 20V at 200mA (Imax). U4 is used as a buck converter for the solar cell,
as it regulates a range of voltages to 5V. The input range for U4 is 7V to 36V, and the output current can
be up to 1.5A, which is somewhat irrelevant because, as previously stated, the maximum current that it
will be receiving is 200mA. The quiescent current for U4 is around 5mA. C3 is a decoupling capacitor for
the lithium polymer battery charger circuitry IC, U3. U3 monitors the voltage of B1 and charges the
battery at a current of up to 200mA (determined by Imax of the solar cells). As the voltage level of B1
decreases, the VBAT pin detects the changes and provides the correct amount of current to charge B1
back to its maximum voltage level (4.2V). This charge current is large (up to 200mA) at low levels, and
small at higher voltage levels (approaching 4.2V). LED1 and R21 that are attached to the STAT pin are
used to show that the LiPo charger is functioning correctly and will cause the LED to light up when the
battery is charging. The output of the solar circuitry is the voltage of B1, which can range from 2.5V
(depleted) to 4.2V (fully charged).
3
3.3V Regulator
Because the voltage that is powering the project comes from a battery, it varies with the charge that the
battery has. The voltage level that is powering the MSP430G2553 needs to be steady, so U1 is used to
regulate the voltage to the commonly used 3.3V level. U1 is a Texas Instruments TPS63001, which is a
SEPIC converter. SEPIC converters act as a BUCK converter if the voltage at the input is higher than the
output voltage level and a BOOST converter if the input voltage level is below the output level. The input
voltage range is 1.8V to 5.5V, which is perfect because the battery B1 can only output voltages between
2.5V and 4.2V. The maximum output current for this module is 800mA, which is far more than the
MSP430G2553 requires. Generally, the MSP430G2553 requires less than 10mA of current, so 800mA
max is more than enough. C1 and C2 are simply used to reduce ripple and decouple the input and
output voltages.
4
6V regulator
As with the 3.3V regulator, the 6V, step up regulator is required to provide a constant voltage level for
the servo and the PIR sensor circuitry. The LT1170 is a high current switching regulator, which is
necessary due to the high current draw from the servo. The servo can pull up to 700mA when
encountering strong resistance, and the maximum output current of the LT1170 at 6V is around 1.5A, so
the LT1170 will be able to supply ample current for both the servo and the PIR sensor. L2 is used as the
means for stepping up the voltage to the 6V level. It has a low inductance value (only 50µH), but it has
an incredibly high current rating (up to 5A). This is because the switch current can exceed the output
current level, and if the inductor is blown than the boost capabilities of the circuit are nullified. The
𝑅23
output voltage of 6V is set by the equation 𝑉𝑜 = 1.244(1 + 𝑅24). Because of this relationship, the
values of R23 and R24 set the feedback level to be such that the output is a constant 6V. The large
capacitor C22 is used to reduce ripple on the output, while C23 provides the same functionality for the
input voltage. R25 and C5 are used to condition the current that flows through Vc, which is used as an
error term in internal voltage reference calculations. Having R25 = 1k and C5 = 1µF is suggested in the
datasheet for typical applications.
5
MSP430G2553 and Servo
The MSP430G2553 is the MCU that this project utilizes. It is powered by the 3.3V regulator as previously
mentioned. C20 and C21 are decoupling caps that reduce any possible ripple coming from the 3.3V
source. P1.7 is connected to the output of the PIR sensor circuitry, and will be used as the main input for
the program’s functionality. The RST pin is tied high through R1 to avoid constant resets (because it is
active low). P2.7 and P2.6 are connected to a 32.7678kHz crystal, X1, which is used by the program to
create reliable 1 second ticks for real time clocking. P1.2 is connected to the gate of the MOSFET, Q1,
which is used to connect the ground pin of the PT-100T servo to the analog ground. This pin essentially
performs enable functionality for the servo. P1.4 is connected to the signal input for the PT-100T servo.
The MSP430 will output a PWM signal over the SERVO_CTRL wire to control the position of the servo
arm. The GND pin of the MSP430 is connected to its own D_GND to prevent noise on the A_GND node
due to CMOS switching. All unused pins are shown as no connects. As per the MSP430 documentation,
these pins should be set to outputs and tied to nothing.
6
Parts List
Item #
Qty
Description
Designator
2
1
BAT-3.7V LIPO SINGLE CELL
B1
4
2
CAP-Cer, X7R, 10uF, 3V, 10%, RAD
C1-2
6
2
CAP-Cer, X7R, 4.7uF, 16V, 10%, RAD
C3-4
8
1
CAP-Cer, X7R, 1uF, 3V, 10%, RAD
C5
10
6
CAP-Cer, X7R, 0.1uF, 16V, 10%, RAD
C6 C8 C14 C17 C19 C21
12
1
CAP-Cer, X7R, 3.3uF, 16V, 10%, RAD
C7
14
1
CAP-Electrolyic, 10% 47uF, 25V
C9
16
2
CAP-Electrolyic, 10% 10uF, 16V
C10-11
18
3
CAP-Cer, X7R, 0.01uF, 16V, 10%, RAD
C12-13 C20
20
3
CAP-Electrolyic, 10% 100uF, 16V
C15-16 C23
22
1
CAP-Electrolyic, 10% 220uF, 16V
C18
24
1
CAP-Electrolyic, 10% 1000uF, 16V
C22
26
1
Diode-Schottky, 1N5817, Axial, 20V, 1A
D1
28
2
DIODE-SWITCH SS 75V 300MA DO35
D2-3
30
1
Diode - Schottky, 30V, 5A
D4
32
1
Inductor- RAD, 2.2uH, 10%, >400mA,
L1
34
1
Inductor- RAD, 50uH, 10%, >5A,
L2
36
1
LIGHT EMITTING DIODE
LED1
38
1
MOTOR-SERVO, DC, 4.8V TO 6V
M1
40
2
MOSFET-N-CH 100V 1.3A 4-DIP
Q1-2
42
1
RES - 5k, 1%, 1/4W, AXIAL
R1
44
2
RES - 47k, 1%, 1/4W, AXIAL
R5 R7
46
3
RES - 18k, 1%, 1/4W, AXIAL
R6 R12 R14
48
1
RES - 1M, 1%, 1/4W, AXIAL
R8
50
2
RES - 15k, 1%, 1/4W, AXIAL
R9 R18
52
2
RES - 100k, 1%, 1/4W, AXIAL
R10 R20
54
1
RES - 2.7M, 1%, 1/4W, AXIAL
R11
56
3
RES - 10k, 1%, 1/4W, AXIAL
R13 R15-16
58
1
RES - 150k, 1%, 1/4W, AXIAL
R17
60
1
RES - 5.1k, 1%, 1/4W, AXIAL
R19
62
1
RES - 470, 1%, 1/4W, AXIAL
R21
64
1
RES - 2k, 1%, 1/4W, AXIAL
R22
66
1
RES - 22.6k, 1%, 1/4W, AXIAL
R23
68
1
RES - 5.9k, 1%, 1/4W, AXIAL
R24
70
1
RES - 1k, 1%, 1/4W, AXIAL
R25
72
1
IC-REG BUCK BST SYNC 3.3V 10SON
U1
74
1
IC-MSP430G2553
U2
76
1
IC-CONTROLLR LI-ION 4.2V SOT23-5
U3
7
78
1
IC - Conv DC/DC, OKI78SR-5/1.5-W36-C, 7.5W, 7-36Vin, 5Vo, 1.5A
U4
80
1
IC-REG MULTI CONFIG ADJ TO220-5
U5
82
1
IC-OPAMP 1.4V QUAD R-R 14SOIC
U6
84
1
CRYSTAL
X1
86
1
IC-PIR SENSOR, D203B
XDCR1
88
1
Solar Cell Bank - 0 to 20V, 0 to 200mA
XDCR2
90
1
DIODE-ZENER 5.1V 1.3W DO41
Z1
8