DHT22, AM2302 and pic18F2320

[bitmaniac]

Hi! my friends!

I am starting a project for my father's home-made incubator egg machine.

Αs I had an DHT22 (ΑΜ2302) humidity sensor in-hand I tried to make a quick code to see if I can use it....

I studied carefully this datasheet http://dlnmh9ip6v2uc.cloudfront.net/...ther/RHT03.pdf
BUT I also found another datasheet elsewhere (I will upload the link as soon as I find the link) with slightly different timming values for starting pulse etc

Here is a rough description of connected circuit + the code I tried out

DHT-22 connected to PORTB.4 of 18F2320
I use NO external pull-up on pin2 (DATA) but pic PORTB PULL-UPS ,instead.

my code:

'***************************************
'*  Name    : 18f2320_DHT22_AM2302.BAS *
'*  Author  : BITmaniac                *
'*  Notice  : Copyright (c) 2013       *
'*  Date    : 1/3/2013                 *
'***************************************

;include "ALLDIGITAL.pbp"
;@ __CONFIG _CONFIG1H, _INTIO2_OSC_1H & _IESO_OFF_1H ' use internal osc
@ __CONFIG _CONFIG1H, _XT_OSC_1H & _IESO_OFF_1H ' use internal osc
@ __CONFIG _CONFIG2L, _PWRT_OFF_2L & _BOR_OFF_2L
@ __CONFIG _CONFIG2H, _WDT_OFF_2H & _WDTPS_512_2H
@ __CONFIG _CONFIG3H, _MCLRE_OFF_3H & _PBAD_DIG_3H ;& _CCP2MX_OFF_3H
@ __CONFIG _CONFIG4L, _LVP_OFF_4L

define osc 4

DEFINE  LCD_DREG        PORTC	' LCD Data Port
DEFINE  LCD_DBIT        4		' Starting Data Bit
DEFINE  LCD_RSREG       PORTC	' Register Select Port
DEFINE  LCD_RSBIT       2		' Register Select Bit
DEFINE  LCD_RWREG       PORTC   ' LCD read/write port 
DEFINE  LCD_RWBIT       1       ' LCD read/write bit 
DEFINE  LCD_EREG        PORTC	' Enable Port
DEFINE  LCD_EBIT        0		' Enable Bit
DEFINE  LCD_BITS		4		' Data Bus Size
DEFINE  LCD_LINES		2		' Number of Lines on LCD
DEFINE  LCD_COMMANDUS 2000
DEFINE  LCD_DATAUS 50
pause 1000

ADCON0=0
ADCON1=00001111                         'All digital
CMCON=7                                 'Comparators OFF
INTCON2.7=0                             'RBPU =0 , TURN ON PORTB PULL-UPS

TRISA=%00000000
TRISB=%00001111


PORTA=0
PORTB=0

humread     var word                    '16-bit var to store humidity
tmpread     var word                    '16-bit var to store temperature
checksum    var BYTE                    '8-bit var to store checksum
x           var byte                    'general var
p           var byte [40]               'store pulse var

led         var LATA.0

clear
high LATA.1:high LATA.2:high LATA.3:high LATA.4
high PORTB.4
;---------- main program -------------
high led
pause 500
LCDout $FE,$1,"DHT-22 sensor"
LCDout $FE,$c0,"reading..."

start:
;---- check_DHT22 ----
;-== send StartSignal ==-
TRISB.4 = 0                             'Data port is output
high PORTB.4
low PORTB.4
pause 20
high PORTB.4
pauseus 20
;-== wait response from Sensor ==-
TRISB.4 = 1                             'Data port is input
while PORTB.4=1:wend                    'wait for low
pauseus 80
while PORTB.4=0:wend                    'wait for high
pauseus 20
low led                                 
;-== read 40bits data from DHT22 ==-
for x=1 to 40
pulsin PORTB.4,1,p(x)                   'measure 40 high pulses only & store  (resoloution is 10us)
next x
;-== convert to '0' & '1' ==-
for x=1 to 40
if p(x)>=2 and p(x)<=4 then p(x)=0      'if pulsewidth between 20 and 40uS then read as '0' 
if p(x)>=6 and p(x)<=8 then p(x)=1      'if pulsewidth between 60 and 80uS then read as '1'
next x
;-== convert bin to dec ==-
humread=32768*p(1)+16384*p(2)+8192*p(3)+4096*p(4)+2048*p(5)+1024*p(6)+512*p(7)+256*p(8)+128*p(9)+64*p(10)+32*p(11)+16*p(12)+8*p(13)+4*p(14)+2*p(15)+1*p(16)
tmpread=16384*p(18)+8192*p(19)+4096*p(20)+2048*p(21)+1024*p(22)+512*p(23)+256*p(24)+128*p(25)+64*p(26)+32*p(27)+16*p(28)+8*p(29)+4*p(30)+2*p(31)+1*p(32)
checksum=128*p(33)+64*p(34)+32*p(35)+16*p(36)+8*p(37)+4*p(38)+2*p(39)+1*p(40)
;-== show real values ==-
;-== show real values ==-
lcdout $fe,$01,"Hum:",dec humread,"% >",dec checksum
lcdout $fe,$C0,"Temp:",dec tmpread,"o"
goto start

(see remarks inside the code)

The problem I have is -as far as I can see- I get response from the sensor BUT with strange results ...see attached foto

Any ideas are welcome...

maybe the problem is with pulsin command trying to catch-up with the sensor pulses.... or timming problems....

Also noticed that I get no CRC checksum data ! (following > charackter in the foto)



Any advice is welcome.

[Demon]

P is defined as byte, but referred as bit?

Edit: what if you display the data you receive, pause a few seconds, then continue. Confirm you're getting data as you expect it.

Edit 2: Does your array start at 0 or 1? (Haven't coded in a while).

Only 17 entries for temp, missing #17.

Robert

[bitmaniac]

P is defined as byte, but referred as bit?

It should be byte as it stores the width of the pulse (in uS) PULSIN receives.
Then it simply stores on itself the value of '1' or '0' according the width of this pulse.

Edit: what if you display the data you receive, pause a few seconds, then continue. Confirm you're getting data as you expect it.

Hmm! I will give it a try and let you knoiw ....Good thoughts my friend!

Edit 2: Does your array start at 0 or 1? (Haven't coded in a while).

I don't think is matter... Arrays start at 0.

Only 17 entries for temp, missing #17.

I just try to not capture the higher bit of temp (1 means temp is below 0 degrees Celsius) for the moment just testing....

Robert Thank you very much for replying

As I can see no example ANYWHERE in the net for DHT22 and picbasic , when completed it would be a good starting point for experiments with this low cost sensor!

[bitmaniac]

In order to find out what pulsin really grabs I used serout data to debug...
Here are the results so far -after reading the sensor 3 times.... :
NOTE I changed the code a little bit so I can capture all data (included the start transmit 1bit before each 'bit')

* * * START * * *
01=> 50uS  bit_val= 1
02=> 20uS  bit_val= 0
03=> 50uS  bit_val= 1
04=> 30uS  bit_val= 1
05=> 50uS  bit_val= 1
06=> 70uS  bit_val= 1
07=> 50uS  bit_val= 1
08=> 70uS  bit_val= 1
09=> 50uS  bit_val= 1
10=> 20uS  bit_val= 0
11=> 50uS  bit_val= 1
12=> 30uS  bit_val= 1
13=> 50uS  bit_val= 1
14=> 20uS  bit_val= 0
15=> 50uS  bit_val= 1
16=> 30uS  bit_val= 1
17=> 70uS  bit_val= 1
18=> 20uS  bit_val= 0
19=> 50uS  bit_val= 1
20=> 60uS  bit_val= 0
21=> 50uS  bit_val= 1
22=> 70uS  bit_val= 1
23=> 50uS  bit_val= 1
24=> 30uS  bit_val= 1
25=> 50uS  bit_val= 1
26=> 20uS  bit_val= 0
27=> 50uS  bit_val= 1
28=> 0uS  bit_val= 0
29=> 0uS  bit_val= 0
30=> 0uS  bit_val= 0
31=> 0uS  bit_val= 0
32=> 0uS  bit_val= 0
33=> 0uS  bit_val= 0
34=> 0uS  bit_val= 0
35=> 0uS  bit_val= 0
36=> 0uS  bit_val= 0
37=> 0uS  bit_val= 0
38=> 0uS  bit_val= 0
39=> 0uS  bit_val= 0
40=> 0uS  bit_val= 0
41=> 0uS  bit_val= 0
42=> 0uS  bit_val= 0
43=> 0uS  bit_val= 0
44=> 0uS  bit_val= 0
45=> 0uS  bit_val= 0
46=> 0uS  bit_val= 0
47=> 0uS  bit_val= 0
48=> 0uS  bit_val= 0
49=> 0uS  bit_val= 0
50=> 0uS  bit_val= 0
51=> 0uS  bit_val= 0
52=> 0uS  bit_val= 0
53=> 0uS  bit_val= 0
54=> 0uS  bit_val= 0
55=> 0uS  bit_val= 0
56=> 0uS  bit_val= 0
57=> 0uS  bit_val= 0
58=> 0uS  bit_val= 0
59=> 0uS  bit_val= 0
60=> 0uS  bit_val= 0
61=> 0uS  bit_val= 0
62=> 0uS  bit_val= 0
63=> 0uS  bit_val= 0
64=> 0uS  bit_val= 0
65=> 0uS  bit_val= 0
66=> 0uS  bit_val= 0
67=> 0uS  bit_val= 0
68=> 0uS  bit_val= 0
69=> 0uS  bit_val= 0
70=> 0uS  bit_val= 0
71=> 0uS  bit_val= 0
72=> 0uS  bit_val= 0
73=> 0uS  bit_val= 0
74=> 0uS  bit_val= 0
75=> 0uS  bit_val= 0
76=> 0uS  bit_val= 0
77=> 0uS  bit_val= 0
78=> 0uS  bit_val= 0
79=> 0uS  bit_val= 0
80=> 0uS  bit_val= 0
* * * END * * *

* * * START * * *
01=> 50uS  bit_val= 1
02=> 20uS  bit_val= 0
03=> 50uS  bit_val= 1
04=> 30uS  bit_val= 1
05=> 50uS  bit_val= 1
06=> 70uS  bit_val= 1
07=> 50uS  bit_val= 1
08=> 70uS  bit_val= 1
09=> 50uS  bit_val= 1
10=> 20uS  bit_val= 0
11=> 50uS  bit_val= 1
12=> 30uS  bit_val= 1
13=> 50uS  bit_val= 1
14=> 20uS  bit_val= 0
15=> 50uS  bit_val= 1
16=> 20uS  bit_val= 0
17=> 70uS  bit_val= 1
18=> 20uS  bit_val= 0
19=> 50uS  bit_val= 1
20=> 70uS  bit_val= 1
21=> 50uS  bit_val= 1
22=> 60uS  bit_val= 0
23=> 50uS  bit_val= 1
24=> 30uS  bit_val= 1
25=> 50uS  bit_val= 1
26=> 20uS  bit_val= 0
27=> 50uS  bit_val= 1
28=> 0uS  bit_val= 0
29=> 0uS  bit_val= 0
30=> 0uS  bit_val= 0
31=> 0uS  bit_val= 0
32=> 0uS  bit_val= 0
33=> 0uS  bit_val= 0
34=> 0uS  bit_val= 0
35=> 0uS  bit_val= 0
36=> 0uS  bit_val= 0
37=> 0uS  bit_val= 0
38=> 0uS  bit_val= 0
39=> 0uS  bit_val= 0
40=> 0uS  bit_val= 0
41=> 0uS  bit_val= 0
42=> 0uS  bit_val= 0
43=> 0uS  bit_val= 0
44=> 0uS  bit_val= 0
45=> 0uS  bit_val= 0
46=> 0uS  bit_val= 0
47=> 0uS  bit_val= 0
48=> 0uS  bit_val= 0
49=> 0uS  bit_val= 0
50=> 0uS  bit_val= 0
51=> 0uS  bit_val= 0
52=> 0uS  bit_val= 0
53=> 0uS  bit_val= 0
54=> 0uS  bit_val= 0
55=> 0uS  bit_val= 0
56=> 0uS  bit_val= 0
57=> 0uS  bit_val= 0
58=> 0uS  bit_val= 0
59=> 0uS  bit_val= 0
60=> 0uS  bit_val= 0
61=> 0uS  bit_val= 0
62=> 0uS  bit_val= 0
63=> 0uS  bit_val= 0
64=> 0uS  bit_val= 0
65=> 0uS  bit_val= 0
66=> 0uS  bit_val= 0
67=> 0uS  bit_val= 0
68=> 0uS  bit_val= 0
69=> 0uS  bit_val= 0
70=> 0uS  bit_val= 0
71=> 0uS  bit_val= 0
72=> 0uS  bit_val= 0
73=> 0uS  bit_val= 0
74=> 0uS  bit_val= 0
75=> 0uS  bit_val= 0
76=> 0uS  bit_val= 0
77=> 0uS  bit_val= 0
78=> 0uS  bit_val= 0
79=> 0uS  bit_val= 0
80=> 0uS  bit_val= 0
* * * END * * *

...remember that I use a 4Mhz crystal so the pulse width is returned in 10us increments.

Acoording to the above dubugging infos we can see a 50uS pulse wich according to datasheet is the pulse before each "0" or "1" pulse!

One weird thing is also tha after pulse number 27 I read no pulses!!

[Demon]

Did you use 100nF capacitor as mentionned in DHT22 datasheet?

Edit: there's a guy here that gets only 21 elements, sounds like a similar issue:
http://www.picaxeforum.co.uk/showthr...22-Please-Help

Edit 2: this is in C, but read the blog at top. Has several interesting comments.
http://blog.ringerc.id.au/2012/01/us...ht-22.html?m=1

Can you run faster than 4mhz? Can you use internal osc instead? 18F generally can go quite fast.

Robert

[bitmaniac]

Thanks for trying to help my problem out my friend!

Yes, I tried with 100nf on power.

I am searching over the net for a week now and came across 2 different datasheet of the same sensor...DHT22 and sites with code in C e.t.c I have read most of them and trying to use picbasic instead!

I will examine carefully your links (VERY good infos!!!) and come back....

[blueocean]

what is lata.0? it's not named in the variables

[mackrackit]

what is lata.0? it's not named in the variables

Yes it is, it is an LED.

[blueocean]

Yes it is, it is an LED.

microcode syntax error on this line:

INTCON2.7=0

and a bad data type on this line:

led var LATA.0

[blueocean]

Yes it is, it is an LED.

but i used a pic16f876a, how can i change those two instructions?

[mackrackit]

Try
PORTA.0