Some of you have voiced your
displeasure with my use of expensive
development tools and I’ve promised
those readers that I would keep my
project costs down as best that I can
for the good of all Design Cycle
readers. So, I’ll try to give you as
complete of an out-of-the-box package as possible, which includes a
ready-to-run compiled hex file you can
load directly into your temperature/
humidity monitor’s PIC18LF6722.
I was talking to a NASA embedded
programmer friend recently and the
discussion wandered into the nuances
of embedded network programming.
All said and done, if a NASA programmer loathes network coding, the
average programming Joe or Joan has
a bit more nasty network programming
water in his or her boat. So, to make
things a bit easier for the Design Cycle
readers, I’ve coded in a comprehensive
networking menu routine into the temperature/humidity monitor firmware.
The temperature/humidity monitor’s built-in menu allows you to
specify the intervals ■ PHOTO 2. This tiny combo
between measurements in sensor outputs a 14-bit
seconds, the temperature/ temperature value and a 12-bit
humidity monitor’s IP humidity value by default. By
programming the Sensirion
address, the target host’s IP SHT15’s Status Register,
address, and the source you can get eight-bit
and destination UDP port humidity readings with 12-bit
numbers. The temperature/ temperature measurements.
humidity monitor menu appears at S e n s i r i o n
power-up via the temperature/ SHT15temper-
humidity monitor’s 56K serial port. If ature/humidity
you don’t want to use the default sensor, which
Wi-Fi SSID of AIRDROP or you want happens to be mounted on our
to use WEP encryption, you’ll have to temperature/humidity monitor PCB.
make those changes in the firmware The Sensirion SHT15 comes in a dual
and recompile. sensor configuration, which provides
Now that you have a lowdown a calibrated digital output. The humid-on all of the temperature/humidity ity sensor component of the Sensirion
monitor’s subsystems and firmware,
let’s begin by taking a closer look
at the hardware that does most all
of the data collection work: the
temperature/humidity sensor.
THE SENSOR
Photo 2 is a bird’s eye view of a
■ SCHEMATIC 1. Note the absence
of a voltage regulator circuit. The
Sensirion SHT15 is very sensitive to
the heating of the printed circuit
board it resides on. Eliminating the
voltage regulator helps to keep the
temperature/humidity monitor’s printed
circuit board cooler. I’ve also left room
so you can route out the printed circuit
board material around the SHT15.
+ 3.3VDC
ICSP CONNECTOR
J1
R1
63
52
41
63
PGC 5 2
10K
R2
U1
PGD 4 1
10K
24
D1
C1
DATA 23
MCLR
.1
1N5819
SCK 22
21
28
27
SP3232 PIN 16 = Vcc
SP3232 PIN 15 = GND
U2
48
47
46
45
44
43
PGC 42
PGD 37
C9 20pF
30
10
TX 11
1
C2
.1uF 3
2
C3
R1IN R1OUT
R2IN R2OUT
T2IN T1OUT
T1IN T2OUT
C1+ C2-
C1-
V+
C2+
V-
RXIN 13 RX
8
12
9
14 TXOUT
7
Y2
C10 20pF
29
5
C5
4
.1uF
6
32.768KHz
33
34
35
36
TX 31
RX 32
C4
.1uF
.1uF
SP3232
SP3232 BYPASS CAP
+ 3.3VDC
RS-232 CONNECTOR
9
8
7
C6
6
5
.1uF
9
8
7
6
5
4
3
2
1
4
RXIN 3
2 TXOUT
1
J2/DB9 FEMALE
RA0 OSC1
RA1
RA2
RA3
RA4 OSC2
RA5
RD0
RB0 RD1
RB1 RD2
RB2 RD3
RB3 RD4
RB4 RD5
RB5 RD6
RB6 RD7
RB7
RE0
RC0 RE1
RE2
RE3
RE4
RC1 RE5
RE6
RE7
RC2
RC3 RF0
RC4 RF1
RC5 RF2
RC6 RF3
RC7 RF4
RF5
RF6
RF7
RG0
RG1
RG2
RG3
RG4
MCLR/RBG5
VDD
AVDD
VDD
VDD
VDD
VSS
AVSS
VSS
VSS
VSS
PIC18LF6722
+ 3.3VDC
C7 20pF
39
Y1
C8 20pF
20MHz
40
58 D00
55 D01
54 D02
53 D03
52 D04
51 D05
50 D06
49 D07
2 A00
1 A01
64 A02
63 A03
62 A04
61 A05
60 A06
59 A07
18 OE
17 IORD
16 REG
15 WAIT
14 RESET
13 IREQ
12 WE
11 IOWR
3 A08
4 A09
5 A10
6
8
7 MCLR
U3
1
DATA 2
SCK 3
4
GND
DATA
SCK
VDD
SHT15
J4
1
D03 2
D04 3
D05 4
D06 5
D07 6
CE1 7
A10 8
OE 9
A09 10
A08 11
+ 3.3VDC A07 12
13
C16 A06 14
A05 15
.1uF A04 16
A03 17
A02 18
A01 19
A00 20
D00 21
D01 22
D02 23
24
25
GND CD1
D03 D11
D04 D12
D05 D13
D06 D14
D07 D15
CE1 CE2
A10 VS1
OE IORD
A09 IOWR
A08 WE
A07 IREQ
VCC VCC
A06 CSEL
A05 VS2
A04 RESET
A03 WAIT
A02 INPACK
A01 REG
A00 BVD2
D00 BVD1
D01 D08
D02 D09
WP D10
CD2 GND
26
27
28
29
30 + 3.3VDC
31
32 CE2
33
34 IORD
35 IOWR
36 WE
37 IREQ + 3.3VDC
38
39 C17
40
41.1uF
42
43
44
45
46
47
48
49
50
RESET
WAIT
REG
CF CARD CONNECTOR
10
19
26
38
57
+ 3.3VDC
+ 3.3VDC
C11 C12 C13 C14 C15
9.1uF .1uF .1uF .1uF .1uF
20
25
41
56
J3
August 2006 75