On Sunday, April 3, 2016 at 7:07:50 AM UTC+5:30, Dennis Lee Bieber wrote:
>
>
> This is a follow up to my prior response...
>
> On Thu, 31 Mar 2016 00:16:28 -0700 (PDT), Sumit Bhut
> <[email protected] <javascript:>> declaimed the following:
>
> >Hi, Dennis Lee Bieber
> >
> >Thanks for the valuable effort but i am unaware of the python language
> and
> >hence it would be really appreciable if you could provide me your help in
> >C/C++ language only.
>
> Python may not have been fast enough for the toggling -- combined
> with
> the fact that time.clock() seemed to have a granularity of 0.01 seconds
> (or
> 10 milliseconds) which would make it difficult to tell how long the time
> was between transitions.
>
> I attempted to generate something in C++ which took hours. For
> some
> reason I can't seem to find a GPIO pin that was actually toggling when
> under an oscilloscope. Even when manually setting the pin value using the
> echo 1 > /sys/class/gpio/gpio#/value
> from a command line. I could read back the 1 (or 0) value, but never found
> a level change on the 'scope -- the pin was either tied high, or tied to
> ground.
>
> My last version is showing some activity, but is still failing, as
> shown (I'm wondering if usleep() has some obscenely large granularity on
> the BBB, because it took 53 seconds to go from "beginning measurement" to
> the first timeout error on the first byte, sixth bit):
>
> debian@beaglebone:~$ sudo ./DHT11
> Beginning measurement pass
>
> Timeout counting bit length 0 5
>
> ***** Error while reading sensor
>
> Beginning measurement pass
>
> Timeout counting bit length 0 6
>
> ***** Error while reading sensor
>
> Beginning measurement pass
>
> Timeout counting bit length 0 5
>
> ***** Error while reading sensor
>
> Beginning measurement pass
>
> Even worst case (all 1 bits) the entire data read (40 bits @ 120
> uSec
> each) is less than 5 msec, and the 20 msec wake up brings the total to
> around <30 msec... So where did the other 53000 msec delay come from?
>
> debian@beaglebone:~$ date && sudo ./DHT11
> Sat Apr 2 21:25:45 EDT 2016
> Beginning measurement pass
>
> Timeout counting bit length 0 3
>
> ***** Error while reading sensor
>
> Beginning measurement pass
>
> Timeout counting bit length 0 4
>
> ***** Error while reading sensor
>
> Beginning measurement pass
> ^Cdebian@beaglebone:~$ date
> Sat Apr 2 21:27:37 EDT 2016
> debian@beaglebone:~$
>
>
> Based upon where it is timing out, the code must be seeing some
> toggling of the signal coming in, or it is reading atmospheric noise; as
> it
> gets past the bus available, wake up response, and a couple of data bits
> --
> all actions that require seeing a LOW then HIGH sequence.
>
> Maybe next weekend I'll have time to convert the deprecated
> usleep()
> into current POSIX nano_sleep(). In the meantime, my code follows. Compile
> with
I tried it with my nanosleep() code as follow:
void pauseNanoSec(long nano)
{
struct timespec tmr1;
tmr1.tv_sec = 0;
tmr1.tv_nsec = nano;
}
>
> g++ -o DHT11 DHT11.cpp -std=c++0x
>
> -=-=-=-=-=-
> /*
> * DHT11.cpp Simple Humidity and Temperature Sensor
> * April 2, 2016 Dennis L Bieber
> *
> * This file defines (and uses) a class to read DHT11 sensors
> * on the BeagleBone Black
> *
> * Minimal error checking is performed, timeout testing is done
> * using cpu-hog polling loops
> *
> * As I've not done C++ in 15 years, there will be some construct
> * that may not be "proper"
> *
> */
>
> #include <iostream>
> #include <cstdio>
> #include <cstdlib>
> #include <cstring>
> #include <ctime>
> #include <unistd.h>
>
> using namespace std;
>
> enum /*class*/ Direction { OUT, IN };
> enum /*class*/ PinState { LOW, HIGH };
>
> struct TimeOutError {};
> struct CheckSumError {};
> struct DHTError {};
>
> class DHT11
> {
> int pinNum;
> long timeOutuSec;
> char pinDirPath[200];
> char pinDataPath[200];
> public:
> DHT11(int pin, int timeOut);
> ~DHT11();
> void readDegC(float &humidity, float &temperature);
> void readDegF(float &humidity, float &temperature);
> private:
> void read(float &humidity, float &temperature);
> void setDir(Direction dir);
> void writePin(PinState value);
> PinState readPin();
> };
>
> DHT11::DHT11(int pin, int timeOut)
> {
> FILE *exportCtl;
>
> // save pin number and timeout values
> // (though pin number may only be used here)
> pinNum = pin;
> timeOutuSec = timeOut * 1000; // msec -> microsec
>
> // export the pin for later access
> exportCtl = fopen("/sys/class/gpio/export", "w");
> fprintf(exportCtl, "%d", pinNum);
> fclose(exportCtl);
>
> // set up the pinData and pinDirCtl paths
> sprintf(pinDataPath, "/sys/class/gpio/gpio%d/value", pinNum);
> sprintf(pinDirPath, "/sys/class/gpio/gpio%d/direction", pinNum);
> }
>
> DHT11::~DHT11()
> {
> FILE *exportCtl;
>
> // unexport the pin for cleanup
> exportCtl = fopen("/sys/class/gpio/unexport", "w");
> fprintf(exportCtl, "%d", pinNum);
> fclose(exportCtl);
> }
>
> void DHT11::setDir(Direction dir)
> {
> FILE *pinDirCtl;
>
> pinDirCtl = fopen(pinDirPath, "w");
> fprintf(pinDirCtl, (IN == dir) ? "in" : "out");
> fclose(pinDirCtl);
> }
>
> void DHT11::writePin(PinState value)
> {
> FILE *pinData;
>
> pinData = fopen(pinDataPath, "w");
> fprintf(pinData, "%d", (HIGH == value) ? 1 : 0);
> fclose(pinData);
> }
>
> PinState DHT11::readPin()
> {
> int pinValue;
> FILE *pinData;
>
> pinData = fopen(pinDataPath, "r");
> fscanf(pinData, "%d", &pinValue);
> fclose(pinData);
>
> return (1 == pinValue) ? HIGH : LOW;
> }
>
> void DHT11::read(float &humidity, float &temperature)
> {
> char data[5] = {0, 0, 0, 0, 0};
> int toCnt;
>
> cout << "Beginning measurement pass" << endl;
>
> // ensure bus is high (no device is pulling it down)
> setDir(IN);
> toCnt = 0;
> try
> {
> while (LOW == readPin())
> {
> toCnt++;
> if (toCnt > timeOutuSec)
> throw TimeOutError {};
> usleep(1);
> }
> }
> catch (TimeOutError)
> {
> cout << endl << "Timeout waiting for bus available" <<
> endl;
> throw DHTError {};
> }
>
> // send wake up signal; spec gives minimum of 18msec
> setDir(OUT);
> writePin(LOW);
> usleep(20 * 1000); // deprecated, should use
> nano_sleep
> writePin(HIGH);
> setDir(IN);
>
> // wait for response start
> toCnt = 0;
> try
> {
> while (HIGH == readPin())
> {
> toCnt++;
> if (toCnt > timeOutuSec)
> throw TimeOutError {};
> usleep(1);
> }
> }
> catch (TimeOutError)
> {
> cout << endl << "Timeout waiting for response start" <<
> endl;
> throw DHTError {};
> }
>
> // wait for response indicator end
> toCnt = 0;
> try
> {
> while (LOW == readPin())
> {
> toCnt++;
> if (toCnt > timeOutuSec)
> throw TimeOutError {};
> usleep(1);
> }
> }
> catch (TimeOutError)
> {
> cout << endl << "Timeout waiting for response indicator
> end" <<
> endl;
> throw DHTError {};
> }
>
> // wait for first data bit start
> toCnt = 0;
> try
> {
> while (HIGH == readPin())
> {
> toCnt++;
> if (toCnt > timeOutuSec)
> throw TimeOutError {};
> usleep(1);
> }
> }
> catch (TimeOutError)
> {
> cout << endl << "Timeout waiting for first bit start" <<
> endl;
> throw DHTError {};
> }
>
> Here I guess we only need the low and high pulses while you have taken
three pulses as high, low and high which I didn't get.
> // loop over 5 data bytes
> for (int i = 0; i < 5; i++)
> {
> // loop over 8 bits per byte
> for (int b = 0; b < 8; b++)
> {
> // wait for actual bit start
> toCnt = 0;
> try
> {
> while (LOW == readPin())
> {
> toCnt++;
> if (toCnt > timeOutuSec)
> throw TimeOutError {};
> usleep(1);
> }
> }
> catch (TimeOutError)
> {
> cout << endl << "Timeout waiting for
> actual data bit " << i
> << " " << b << endl;
> throw DHTError {};
> }
>
> // accumulate microseconds for duration of
> bit
> // until start of next bit signal
> toCnt = 0;
> try
> {
> while (HIGH == readPin())
> {
> toCnt++;
> if (toCnt > timeOutuSec)
> throw TimeOutError {};
> usleep(1);
> }
> }
> catch (TimeOutError)
> {
> cout << endl << "Timeout counting bit
> length " << i << " "
> << b << endl;
> throw DHTError {};
> }
>
> // determine short or long (0 or 1)
> if (toCnt > 45)
on what basis did you took this value 44 here?
>
data[i] = (data[i] << 1) + 1;
> else
> data[i] = (data[i] << 1) + 0;
>
> }
> }
>
> // checksum computation
> if ((data[0] + data[1] + data[2] + data[3]) % 256 != data[4])
> throw CheckSumError {};
>
> humidity = (float) data[0] + ((float) data[1] / 10.0);
> temperature = (float) data[2] + ((float) data[3] / 10.0);
> }
>
> void DHT11::readDegC(float &humidity, float &temperature)
> {
> // reports are that one should read twice as the first
> // read contains stale data
> read(humidity, temperature);
> read(humidity, temperature);
> }
>
> void DHT11::readDegF(float &humidity, float &temperature)
> {
> readDegC(humidity, temperature);
> // convert degC to degF
> temperature = (temperature * 9.0) / 5.0 + 32.0;
> }
>
> int main(int argc, char *argv[])
> {
> DHT11 mySensor = DHT11{48, 200}; // P9_15, 200mSec
> time-out
>
> float humidity;
> float temperature;
>
> try
> {
> while (1)
> {
> try
> {
> mySensor.readDegF(humidity, temperature);
> cout << "Humidity: " << humidity << "%\t"
> << "Temperature: " << temperature
> << " degF" << endl;
> sleep(5);
> }
> catch (CheckSumError)
> {
> cout << endl << "***** Checksum mismatch"
> << endl << endl;
> }
> catch (DHTError)
> {
> cout << endl << "***** Error while reading
> sensor" << endl
> << endl;
> }
> }
> }
> catch (...)
> {
> // Any exception should take this route
> cout << endl << "***** Something failed, I won't tell you
> what" <<
> endl << endl;
> }
>
> return (0);
> }
> -=-=-=-=-=-
> --
> Wulfraed Dennis Lee Bieber AF6VN
> [email protected] <javascript:> HTTP://wlfraed.home.netcom.com/
>
> Here also the problem remains the same as in my code, we are not able to
initialize the DHT11 sensor somehow... but yeah on a surprising note this
link proved to be quite handy in fetching the data from the sensor though
as i am not acquainted with python, whatever is happening inside the code
is mysterious to me.
https://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging/software-install-updated
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