A library for the use of AM2303 (a.k.a. DHT22), a temperature and humidity sensor.
Dependents: AM2303_Hello_World
Fork of DHT11 by
AM2303.cpp
- Committer:
- s_inoue_mbed
- Date:
- 2014-10-13
- Revision:
- 12:1ad0612823e9
- Parent:
- DHT11.cpp@ 11:e91c151d1798
File content as of revision 12:1ad0612823e9:
/* Copyright (c) 2014 Shigenori Inoue, MIT License * * Permission is hereby granted, free of charge, to any person obtaining a copy of this software * and associated documentation files (the "Software"), to deal in the Software without restriction, * including without limitation the rights to use, copy, modify, merge, publish, distribute, * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in all copies or * substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */ #include "AM2303.h" // Constructor AM2303::AM2303(PinName pin) : io(pin, PIN_INPUT, OpenDrain, 1), io_irq(pin) { io_irq.rise(this, &AM2303::pos_edge); io_irq.fall(this, &AM2303::neg_edge); io_irq.disable_irq(); io_irq.mode(OpenDrain); t.start(); first_time = true; } // Destructor AM2303::~AM2303(void) {} // Constants const int AM2303::t_tol_start = 100; const int AM2303::t_tol_pulse = 10; // Reading the data bits from the AM2303 int AM2303::readData(void) { // Checking the measurement frequency if (t.read_ms() < 2000 && first_time == false) { t.reset(); return READ_TOO_OFTEN; } // Initialize init(); // Checking the data bus if (io == 0) { t.reset(); return BUS_BUSY; } // Sending start signal, low signal for around 10 ms t.reset(); io.output(); io = 0; do { } while (t.read_us() < 1000 + t_tol_start); io.input(); io = 1; // Waiting for the start of the response signal t.reset(); do { if (t.read_us() > 100) { t.reset(); return NOT_PRESENT; } } while (io == 1); // Wainting for the start of the ready signal t.reset(); do { if (t.read_us() > 100) { t.reset(); return NOT_READY; } } while (io == 0); // Wainting for the end of the ready signal t.reset(); do { if (t.read_us() > 100) { t.reset(); return WATCHDOG_ERR; } } while (io == 1); // Starting the pulse width sensing // by the use of interruptions io_irq.enable_irq(); do { wait_us(100); if (wdt > 50) { t.reset(); return WATCHDOG_ERR; } wdt++; } while (eod == false); // Calculating the check sum chksum = ((data & 0xff00000000) >> 32) + ((data & 0x00ff000000) >> 24) + ((data & 0x0000ff0000) >> 16) + ((data & 0x000000ff00) >> 8); if ((chksum & 0xff) != (data & 0x00000000ff)) { t.reset(); return CHKSUM_ERR; } else { t.reset(); first_time = false; return OK; } } // Extracting humidity data from the received data float AM2303::readHumidity(void) { return static_cast<float>((data & 0xffff000000) >> 24) / 10; } // Extracting temperature data from the received data float AM2303::readTemperature(void) { return static_cast<float>((data & 0x0000ffff00) >> 8) / 10; } // Initialization of variables void AM2303::init(void) { t_pulse_us = 0; data = 0; chksum = 0; cnt = 0; wdt = 0; eod = false; t.reset(); } void AM2303::pos_edge(void) { // Disabling the interruptions io_irq.disable_irq(); // Initializing the Timer t.reset(); // Enabling the interruptions io_irq.enable_irq(); } void AM2303::neg_edge(void) { // Disabling the interruptions io_irq.disable_irq(); // Reading the positive pulse width t_pulse_us = t.read_us(); // Detecting 0 if the pulse width ranges around 25 us if (25 - t_tol_pulse <= t_pulse_us && t_pulse_us <= 30 + t_tol_pulse) { // Shifting the data buffer and not adding 1 (because this bit is zero) data = data << 1; // Counting up the bits cnt++; } // Detecting 1 if the pulse width ranges from 70 us else if (70 - t_tol_pulse <= t_pulse_us && t_pulse_us <= 70 + t_tol_pulse) { // Shifting the data buffer and adding 1 (because this bit is one) data = data << 1; data++; // Counting up the bits cnt++; } // Detecting the end of Data if (cnt < 40) { // Enabling the interruptions io_irq.enable_irq(); } else { eod = true; } }