OrangePi Zero LTS vs DHT22

[DoubleHP]

Hello.

 

First, I have an LTS board that provides only 3.05 on the 3.3 pins. Is it normal ?

 

Anyway, in case this was the issue, I have built a new voltage regulator, and now supply the DHT22 and pullup resistor with 3.60V

 

My issue is simple: when plugged on normal 1W bus, the DHT22 kills the bus, and makes other devices non working. I have moved all other devices on a new bus, leaving the DHT on a bus I know works fine. Some people mentionned the DHT is not compliant with official 1W libraries, and can not be recognised with normal timings, so, special libs are required. I have removed param_w1_pin=PA06 for the hysical pin 7, and installed new software.

 

I have a very bad experience with python, and I have never been able to make any python lib/project, on any board of any brand; I always get some error at some point.

 

The only non python lib/app for DHT22 I have found is

https://github.com/pilkch/climbatize

but after heavily patching it (to fix various bugs), the app still seems unable to communicate with the probe.

 

I have checked more than 12 times the sensor is connected to the so called pin 7 (PA06), pin 2 in WiringPi, and changed the physical sensor (paid for  a new item).

 

Who can help reading this probe ? I am just running out of ideas.

 

The only issue that bothers me is that I am not physically 100% certain that Climbatize manipulates pin7. I have entered the loop that manipulates some pin, but at some point it's calling wiringPi, and my multimeter always shows 3.6V on the pin; I don't have a scope to check the pin goes down, and applying a LED on a pulledup pin will not produce a perceptible OFF time. I would need to solder an inverted gate to transform the logic, but even then, the light pulses may be too short for my eyes.

 

I really dont think 3.60V could burn the oPi board; and 3.05 could be a huge reason  for the DHT22 to refuse to work. I could plug a lab regulated supply, but I think it would be overkill.

 

I do have spare/new/unused boards; but all my LTS boards deliver 3.05. (yes I have some boards left in 2022; I had bought *MANY* spare ones years ago).

[DoubleHP]

For example, I see a /lib/modules/./4.13.16-sunxi/kernel/drivers/iio/humidity/dht11.ko , how can I try using this ?

[DoubleHP]

WORKS FOR ME

 

It was my VERY LAST try before giving up completely:

https://www.uugear.com/portfolio/read-dht1122-temperature-humidity-sensor-from-raspberry-pi/

fix the ping to 7 (instead of 3 in the source), compile with

cc -Wall dht.c -o dht -lwiringPi -pthread

 

and it does the job:

 

Quote

./dht
Raspberry Pi DHT11/DHT22 temperature/humidity test
Humidity = 46.0 % Temperature = 23.5 *C (74.3 *F)
Humidity = 37.9 % Temperature = 27.4 *C (81.3 *F)
Data not good, skip
Data not good, skip
Data not good, skip
Data not good, skip
Humidity = 37.5 % Temperature = 27.2 *C (81.0 *F)
Data not good, skip
Data not good, skip
Humidity = 37.7 % Temperature = 27.2 *C (81.0 *F)
Data not good, skip
Humidity = 37.6 % Temperature = 27.2 *C (81.0 *F)
Humidity = 37.6 % Temperature = 27.2 *C (81.0 *F)
Data not good, skip
Data not good, skip
Data not good, skip
Data not good, skip
Humidity = 37.6 % Temperature = 27.2 *C (81.0 *F)
Data not good, skip
Humidity = 37.7 % Temperature = 27.2 *C (81.0 *F)
Humidity = 37.6 % Temperature = 27.3 *C (81.1 *F)
Data not good, skip
Humidity = 37.7 % Temperature = 27.3 *C (81.1 *F)
Data not good, skip
Data not good, skip
Data not good, skip
Humidity = 37.6 % Temperature = 27.2 *C (81.0 *F)
Humidity = 37.6 % Temperature = 27.3 *C (81.1 *F)
Data not good, skip
Data not good, skip
Data not good, skip
Humidity = 37.7 % Temperature = 27.3 *C (81.1 *F)
Humidity = 37.6 % Temperature = 27.3 *C (81.1 *F)
Data not good, skip

 

According to other forums, 60% misses is ordinary for this probe.

 

Note that the very first value is completely wrong; I did not read anything about this, but I am not surprised. CO2 probes need 15 pre heat; and this is the very first successfull read of the probe, so some miss-configuration or badly initialised variable are likely. So, on production line, I will take care to ignore the first 3 values after service start/reboot.

 

 

[DoubleHP]

In case the other website goes down, I will duplicate their original code here. Don't forget to fix your PIN number.

 

My WiringPi lib is probably https://github.com/zhaolei/WiringOP (not 100% certain).

 

/*
 *  dht.c:
 *    read temperature and humidity from DHT11 or DHT22 sensor
 */
#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#define MAX_TIMINGS    85
#define DHT_PIN        3    /* GPIO-22 */
int data[5] = { 0, 0, 0, 0, 0 };
void read_dht_data()
{
    uint8_t laststate    = HIGH;
    uint8_t counter        = 0;
    uint8_t j            = 0, i;
    data[0] = data[1] = data[2] = data[3] = data[4] = 0;
    /* pull pin down for 18 milliseconds */
    pinMode( DHT_PIN, OUTPUT );
    digitalWrite( DHT_PIN, LOW );
    delay( 18 );
    /* prepare to read the pin */
    pinMode( DHT_PIN, INPUT );
    /* detect change and read data */
    for ( i = 0; i < MAX_TIMINGS; i++ )
    {
        counter = 0;
        while ( digitalRead( DHT_PIN ) == laststate )
        {
            counter++;
            delayMicroseconds( 1 );
            if ( counter == 255 )
            {
                break;
            }
        }
        laststate = digitalRead( DHT_PIN );
        if ( counter == 255 )
            break;
        /* ignore first 3 transitions */
        if ( (i >= 4) && (i % 2 == 0) )
        {
            /* shove each bit into the storage bytes */
            data[j / 8] <<= 1;
            if ( counter > 16 )
                data[j / 8] |= 1;
            j++;
        }
    }
    /*
     * check we read 40 bits (8bit x 5 ) + verify checksum in the last byte
     * print it out if data is good
     */
    if ( (j >= 40) &&
         (data[4] == ( (data[0] + data[1] + data[2] + data[3]) & 0xFF) ) )
    {
        float h = (float)((data[0] << 8) + data[1]) / 10;
        if ( h > 100 )
        {
            h = data[0];    // for DHT11
        }
        float c = (float)(((data[2] & 0x7F) << 8) + data[3]) / 10;
        if ( c > 125 )
        {
            c = data[2];    // for DHT11
        }
        if ( data[2] & 0x80 )
        {
            c = -c;
        }
        float f = c * 1.8f + 32;
        printf( "Humidity = %.1f %% Temperature = %.1f *C (%.1f *F)\n", h, c, f );
    }else  {
        printf( "Data not good, skip\n" );
    }
}
int main( void )
{
    printf( "Raspberry Pi DHT11/DHT22 temperature/humidity test\n" );
    if ( wiringPiSetup() == -1 )
        exit( 1 );
    while ( 1 )
    {
        read_dht_data();
        delay( 2000 ); /* wait 2 seconds before next read */
    }
    return(0);
}

 

[atomic77]

Thank you for sharing this! I have a DHT22 that i've been trying to get working with an OrangePi Lite and I've had terrible results with all of the python-based libraries i've tried. I'm getting about 25-30% of the readings with this every 2s, which is good enough for my purposes.

 

FWIW, my opi lite is showing about 5.2 and 3.8v for the 5V and 3.3V pins