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Driver For SHT75 Temperature & Humidity Sensor
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aslan



Joined: 11 Jul 2011
Posts: 1

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PostPosted: Mon Jul 11, 2011 4:21 am     Reply with quote

jecottrell wrote:
delene wrote:
My code also returns -4.6 and -39.9... :(

I have tried the suggestions above and still no joy
Any other suggestions???



I know this is an old topic, but I thought I'd post for future readers...

I had a similar problem after laying out a new board and accidentally swapping the data and clock lines. Got them squared away and it works fine.

So, double check your pin defines in the driver file.


Use "port_x_pullups(TRUE);" at the beginning of the main function.
x is the port name you use for sht data-clock lines.
output_float effects.. for example:
Code:

void main( ) // Main block
{   

   float restemp, truehumid;
   
   setup_psp(PSP_DISABLED);
   
   lcd_init();   
    sht_init();
    port_b_pullups(TRUE);                 //here you add this line
                                          //remove external pull-up
lazuribicci



Joined: 06 Feb 2010
Posts: 10

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The exact solution about reading -40ºC
PostPosted: Fri Jul 20, 2012 3:15 pm     Reply with quote

Hello friends,

I want to share my experiences about reading -40ºC.

Some sensors work well but the some doesn't work with same hardware and software. is the sensor broken? Actually it is not...
the problem is polymers inside the sensor. The polymers need re-hydration.

Some sensors that I used doesn't read temperature and humidity properly. In such cases, put the sensor into the water and let stand for one day. After that sensor works very well Smile

Quote from datasheet.
Quote:

IMPORTANT: After soldering the devices should be stored
at >75%RH for at least 12h to allow the polymer to rehydrate.
Otherwise the sensor may read an offset that
slowly disappears if exposed to ambient conditions.
Alternatively the re-hydration process may be performed at
ambient conditions (>40%RH) during more than 5 days.
lazuribicci



Joined: 06 Feb 2010
Posts: 10

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PostPosted: Sun Jul 22, 2012 4:20 am     Reply with quote

Another solution:

bake the PCB card with sensored at 100ºC for a couple of hours Smile
I have saved many sensors with these methods.
Gabriel



Joined: 03 Aug 2009
Posts: 964
Location: Panama

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PostPosted: Fri Jun 21, 2013 7:44 am     Reply with quote

I tried this code and IT WORKS... straight out of the box.

However, I did have some problems with the output formating.
Code:
  printf(lcd_putc, "Temp : %3.1f %cC   ", restemp, 223);
  printf(lcd_putc, "\nRH   : %3.1f %%   ", truehumid);


After re-coding the Printf's to print to a PC terminal, via FTDI, it was all good.
Code:
printf("T: %3.1fC - RH: %3.1f%%\n\r", restemp, truehumid);


I do not know if the reading were precise or not since i didnt have another temp/RH sensor around, but they seemed about right.

response time was good, humidity and temp changed accordingly when i exhaled on the sensor...

My setup:
PIC16F886 @ 20MHz
PCM 4.135 + MPLAB 8.85
5V
SHT15 - Scavenged from a HOBO datalogger.
FTDI for TX/RX

I noticed this code is from 2006, so i will be updating small things like:

Code:
 for(i=0; i<9; i++)
  {
   output_bit(sht_clk_pin, 1);  //toggle clk 9 times
   delay_us(2);
   output_bit(sht_clk_pin, 0);
   delay_us(2);
 }


with simpler things like: output_toggle(sht_clk_pin)

... and will re-post with due credit to Hansolo


Thank you Hansolo for posting this.

G.
_________________
CCS PCM 4.135 & CCS PCH 5.013
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