add dhtreader example

Author: houqp

Adafruit_DHT_Driver_Python/README.md

@@ -0,0 +1,25 @@
+Build dependencies for dhtreader python library
+
+* python-dev
+* bcm2835 library: http://www.airspayce.com/mikem/bcm2835/
+
+Run following command to build the library:
+```
+python setup.py build
+```
+
+After that you should be able to find a dhtreader.so file inside `build`
+directory. Put that library file in the same directory with your Python script,
+then you are good to go.
+
+Usage example:
+
+```python
+import dhtreader
+
+type = 22
+pin = 24
+
+dhtreader.init()
+print dhtreader(type, pin)
+```

Adafruit_DHT_Driver_Python/dhtreader.c

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+/*  Python module for DHT temperature/humidity sensors
+ *
+ *  Modified by Qingping Hou from DHT reader example, original header:
+ *
+ *  How to access GPIO registers from C-code on the Raspberry-Pi
+ *  Example program
+ *  15-January-2012
+ *  Dom and Gert
+ */
+
+
+/* for usleep */
+#define _BSD_SOURCE
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <dirent.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <bcm2835.h>
+#include <unistd.h>
+
+#include <Python.h>
+
+#define MAXTIMINGS 100
+
+//#define DEBUG
+
+#define DHT11 11
+#define DHT22 22
+#define AM2302 22
+
+int readDHT(int type, int pin, float *temp_p, float *hum_p)
+{
+	int counter = 0;
+	int laststate = HIGH;
+	int i = 0;
+	int j = 0;
+	int checksum = 0;
+#ifdef DEBUG
+	int bitidx = 0;
+	int bits[250];
+#endif
+	int data[100];
+
+	// Set GPIO pin to output
+	bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP);
+
+	bcm2835_gpio_write(pin, HIGH);
+	usleep(500000);  // 500 ms
+	bcm2835_gpio_write(pin, LOW);
+	usleep(20000);
+
+	bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT);
+
+	data[0] = data[1] = data[2] = data[3] = data[4] = 0;
+
+	// wait for pin to drop?
+	while (bcm2835_gpio_lev(pin) == 1) {
+		usleep(1);
+	}
+
+	// read data!
+	for (i = 0; i < MAXTIMINGS; i++) {
+		counter = 0;
+		while ( bcm2835_gpio_lev(pin) == laststate) {
+			counter++;
+			//nanosleep(1);		// overclocking might change this?
+			if (counter == 1000)
+				break;
+		}
+		laststate = bcm2835_gpio_lev(pin);
+		if (counter == 1000) break;
+#ifdef DEBUG
+		bits[bitidx++] = counter;
+#endif
+
+		if ((i>3) && (i%2 == 0)) {
+			// shove each bit into the storage bytes
+			data[j/8] <<= 1;
+			if (counter > 200)
+				data[j/8] |= 1;
+			j++;
+		}
+	}
+
+#ifdef DEBUG
+	for (int i=3; i<bitidx; i+=2) {
+		printf("bit %d: %d\n", i-3, bits[i]);
+		printf("bit %d: %d (%d)\n", i-2, bits[i+1], bits[i+1] > 200);
+	}
+	printf("Data (%d): 0x%x 0x%x 0x%x 0x%x 0x%x\n", j, data[0], data[1], data[2], data[3], data[4]);
+#endif
+
+	if (j >= 39) {
+		checksum = (data[0] + data[1] + data[2] + data[3]) & 0xFF;
+		if (data[4] == checksum) {
+			/* yay! checksum is valid */
+			if (type == DHT11) {
+				/*printf("Temp = %d *C, Hum = %d \%\n", data[2], data[0]);*/
+				*temp_p = (float)data[2];
+				*hum_p = (float)data[0];
+			} else if (type == DHT22) {
+				*hum_p = data[0] * 256 + data[1];
+				*hum_p /= 10;
+
+				*temp_p = (data[2] & 0x7F)* 256 + data[3];
+				*temp_p /= 10.0;
+				if (data[2] & 0x80)
+					*temp_p *= -1;
+				/*printf("Temp =  %.1f *C, Hum = %.1f \%\n", f, h);*/
+			}
+			return 0;
+		}
+		return -2;
+	}
+
+	return -1;
+}
+
+
+static PyObject *
+dhtreader_init(PyObject *self, PyObject *args)
+{
+	return Py_BuildValue("i", bcm2835_init());
+}
+
+static PyObject *
+dhtreader_read(PyObject *self, PyObject *args)
+{
+	int type, dhtpin;
+
+	if (!PyArg_ParseTuple(args, "ii", &type, &dhtpin))
+		return NULL;
+
+	float t, h;
+	int re = readDHT(type, dhtpin, &t, &h);
+
+	if (re == 0) {
+		return Py_BuildValue("(d,d)", t, h);
+	} else if (re == -1) {
+#ifdef DEBUG
+		printf("sensor read failed! not enough data received\n");
+#endif
+	} else if (re == -2) {
+#ifdef DEBUG
+		printf("sensor read failed! checksum failed!\n");
+#endif
+	}
+
+	return Py_BuildValue("");
+}
+
+
+static PyMethodDef DHTReaderMethods[] = {
+	{"init", dhtreader_init, METH_VARARGS,
+	 "initialize dht reader"},
+	{"read", dhtreader_read, METH_VARARGS,
+	 "temperature and humidity from sensor"},
+    {NULL, NULL, 0, NULL}        /* Sentinel */
+};
+
+PyMODINIT_FUNC
+initdhtreader(void)
+{
+    PyObject *m;
+
+    m = Py_InitModule("dhtreader", DHTReaderMethods);
+    if (m == NULL)
+        return;
+}
+
+

Adafruit_DHT_Driver_Python/setup.py

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+#!/usr/bin/env python
+# -*- coding:utf-8 -*-
+
+from distutils.core import setup, Extension
+
+dht_mod = Extension('dhtreader',
+                    include_dirs = ['.'],
+                    libraries = ['bcm2835'],
+                    sources = ['dhtreader.c'])
+
+setup (name = 'dhtreader',
+       version = '1.0',
+       description = 'Python library to interface with dht sensors',
+       ext_modules = [dht_mod])