Nuts & Volts - August 2006

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 _IPhumidity 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

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

^C820pF

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