雖然
Grove – Temperature and Humidity Sensor Pro
中文 Go pro in temperature and relative humidity measurement applications with this Grove gadget. This is a powerful sister version of our Grove – Temperature and Humidity Sensor. It has more complete and accurate performance than the basic version. The detecting range of this sensor is 5% RH – 99% RH, and -40°C – 80°C. And its accuracy satisfyingly reaches up to 2% RH and 0.5°C. A professional choice for applications that have relatively strict requirements.
Specification
| Item | Parameter | Min | Norm | Max | Unit |
|---|---|---|---|---|---|
| VCC | – | 3.3 | – | 6 | V |
| Measuring Current Supply | – | 1 | – | 1.5 | mA |
| Standby Current Supply | – | 40 | – | 50 | uA |
| Measuring range | Humidity | 5% | – | 99% | RH |
| Temperature | -40 | – | 80 | °C | |
| Accuracy | Humidity | – | – | ±2% | RH |
| Temperature | – | – | ±0.5 | °C | |
| Resolution | Humidity | – | – | 0.1% | RH |
| Temperature | – | – | 0.1 | °C | |
| Repeatability | Humidity | – | – | ±0.3% | RH |
| Temperature | – | – | ±0.2 | °C | |
| Long-term Stability | – | – | – | ±0.5% | RH/year |
| Signal Collecting Period | – | – | 2 | – | S |
| Respond Time | 1/e(63%) | 6 | – | 20 | S |
───
是連接在『小樹林系統』之『數位埠』上，但是只要粗略考察 Grove System 派生界面原始碼︰
【 GrovePi/Software/Python/grovepi.py 】
# line 284
# Read and return temperature and humidity from Grove DHT Pro
def dht(pin, module_type):
write_i2c_block(address, dht_temp_cmd + [pin, module_type, unused])
# Delay necessary for proper reading fron DHT sensor
time.sleep(.6)
try:
read_i2c_byte(address)
number = read_i2c_block(address)
time.sleep(.1)
if number == -1:
return -1
except (TypeError, IndexError):
return -1
# data returned in IEEE format as a float in 4 bytes
if p_version==2:
h=''
for element in (number[1:5]):
h+=chr(element)
t_val=struct.unpack('f', h)
t = round(t_val[0], 2)
h = ''
for element in (number[5:9]):
h+=chr(element)
hum_val=struct.unpack('f',h)
hum = round(hum_val[0], 2)
else:
t_val=bytearray(number[1:5])
h_val=bytearray(number[5:9])
t=round(struct.unpack('f',t_val)[0],2)
hum=round(struct.unpack('f',h_val)[0],2)
return [t, hum]
以及韌體 Source Code ︰
【 GrovePi/Firmware/Source/v1.2/grove_pi_v1_2_5/DHT.cpp 】
# line 82
boolean DHT::read(void) {
uint8_t laststate = HIGH;
uint8_t counter = 0;
uint8_t j = 0, i;
unsigned long currenttime;
// pull the pin high and wait 250 milliseconds
digitalWrite(_pin, HIGH);
delay(250);
currenttime = millis();
if (currenttime < _lastreadtime) {
// ie there was a rollover
_lastreadtime = 0;
}
if (!firstreading && ((currenttime - _lastreadtime) < 2000)) {
return true; // return last correct measurement
//delay(2000 - (currenttime - _lastreadtime));
}
firstreading = false;
/*
Serial.print("Currtime: "); Serial.print(currenttime);
Serial.print(" Lasttime: "); Serial.print(_lastreadtime);
*/
_lastreadtime = millis();
data[0] = data[1] = data[2] = data[3] = data[4] = 0;
// now pull it low for ~20 milliseconds
pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
delay(20);
cli();
digitalWrite(_pin, HIGH);
delayMicroseconds(40);
pinMode(_pin, INPUT);
// read in timings
for ( i=0; i< MAXTIMINGS; i++) {
counter = 0;
while (digitalRead(_pin) == laststate) {
counter++;
delayMicroseconds(1);
if (counter == 255) {
break;
}
}
laststate = digitalRead(_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 > _count)
data[j/8] |= 1;
j++;
}
}
sei();
/*
Serial.println(j, DEC);
Serial.print(data[0], HEX); Serial.print(", ");
Serial.print(data[1], HEX); Serial.print(", ");
Serial.print(data[2], HEX); Serial.print(", ");
Serial.print(data[3], HEX); Serial.print(", ");
Serial.print(data[4], HEX); Serial.print(" =? ");
Serial.println(data[0] + data[1] + data[2] + data[3], HEX);
*/
// check we read 40 bits and that the checksum matches
if ((j >= 40) &&
(data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) ) {
return true;
}
return false;
}
就可以發現這可不是簡單的『 0 』與『 1 』狀態而已，而是一種『單線』 One Wire 種類之『存取規範』。因此必須細讀 AM2302 溫‧濕度感測器之 Data Sheet ︰
才能了解與解讀韌體寫作的程式邏輯。
雖說樹莓派上也有
1-Wire
1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signaling, and power over a single signal.[1] 1-Wire is similar in concept to I²C, but with lower data rates and longer range. It is typically used to communicate with small inexpensive devices such as digital thermometers and weather instruments. A network of 1-Wire devices with an associated master device is called a MicroLAN.
One distinctive feature of the bus is the possibility of using only two wires: data and ground. To accomplish this, 1-Wire devices include an 800 pF capacitor to store charge, and to power the device during periods when the data line is active.
───
GPIO 界面，之前在《勇闖新世界︰ 《 Kernel 4.X 》之整裝蓄勢‧事件驅動 →→ 設備管理及應用》文本中也曾談過︰
最後就讓我們再次回到『DS18B20』數位環境溫度感測器，當我們已經設定了『w1-gpio』的 dtoverlay ，也安裝了感測器，我們怎麼知道裝置正確工作了呢？也許可以用
pi@raspberrypi ~cd /sys/bus/w1/devices/ # 28-021463ab43ff 某個『DS18B20』數位環境溫度感測器 pi@raspberrypi /sys/bus/w1/devices
cd 28-021463ab43ff pi@raspberrypi /sys/bus/w1/devices/28-021463ab43ff
cat name 28-021463ab43ff # 第一行的 YES 代表第二行溫度取得正確，若是 NO 代表溫度取得錯誤。 # 讀取溫度， t=35937 意味 35937/1000 = 35.937 °C pi@raspberrypi /sys/bus/w1/devices/28-021463ab43ff
*** QuickLaTeX cannot compile formula: cat w1_slave 3f 02 55 00 7f ff 0c 10 89 : crc=89 YES 3f 02 55 00 7f ff 0c 10 89 t=35937 </pre> <span style="color: #808000;">這 個古怪的『類檔案裝置界面』顯然不怎麼對『使用者友善』 user friendly ，要是想一想所謂的『API』，指應用程式界面，原本就是設計給『程式』用的，自然就可以釋懷的了。即使是『程式』應用 ，『界面』也有使用上方便與否的問題，所以為『界面』再寫個易使用的『程式庫』，包裹成易記易讀的『新界面』也是常有的事。《 <a href="https://www.freesandal.org/?m=20150626"><span style="color: #808000;">M♪o 之學習筆記本《巳》文章︰【䷡】藩決不羸</span></a>》文本裡的 《<a href="https://github.com/timofurrer/w1thermsensor"><span style="color: #808000;">W1ThermSensor</span></a>》 就是這一類的『程式庫』。建議讀者閱讀它的『原始碼』《<a href="https://github.com/timofurrer/w1thermsensor/blob/master/w1thermsensor/core.py"><span style="color: #808000;">core.py</span></a>》，思索設備『應用』以及『管理』方法，或將能夠對『程式實務』有更深的認識耶！</span>！ ─── <span style="color: #666699;">畢竟類似歸類似，規範不同，『 w1-gpio 』恐難以介接也！所以說即使只是『一根』數位線而已，其內可能之文章，當真『大哉問』的耶？再者若從此感測器『規範』之『時序條件』需求來講，想自樹莓派直接以 Digital Read/Write 方式來控制，也是不切實際的了 ！！？？</span> <span style="color: #666699;">就像『室內舒適度』雖然可以假設為</span> <span style="color: #808080;">風速接近於零</span> <span style="color: #666699;">。且將<a style="color: #666699;" href="http://www.twwiki.com/wiki/%E4%BA%BA%E9%AB%94%E8%88%92%E9%81%A9%E5%BA%A6%E6%8C%87%E6%95%B8">人體舒適度指數</a>︰</span> *** Error message: You can't use `macro parameter character #' in math mode. leading text: <span style="color: # Unicode character 這 (U+9019) leading text: <span style="color: #808000;">這 Unicode character 個 (U+500B) leading text: <span style="color: #808000;">這 個 Unicode character 古 (U+53E4) leading text: <span style="color: #808000;">這 個古 Unicode character 怪 (U+602A) leading text: <span style="color: #808000;">這 個古怪 Unicode character 的 (U+7684) leading text: ...n style="color: #808000;">這 個古怪的 Unicode character 『 (U+300E) leading text: ...tyle="color: #808000;">這 個古怪的『 Unicode character 類 (U+985E) leading text: ...e="color: #808000;">這 個古怪的『類 Unicode character 檔 (U+6A94) leading text: ...color: #808000;">這 個古怪的『類檔SSD \ = \ (1.818 \times \ T \ + \ 18.18) \times \ (0.88 \ + \ 0.002 \ \times \ H) \ + \ \frac{(T \ - \ 32)}{(45 \ - \ T)} \ - \ 3.2 \times \ W \ + \ 18.2
(1.818 \times \ T \ + \ 18.18) \times \ (0.88 \ + \ 0.002 \ \times \ H) \ + \ \frac{(T \ - \ 32)}{(45 \ - \ T)} \ + \ 18.2$
就好！若問程式『加寫』在哪好呢？依舊是『費思量』的哩？？？
, 
and D.
, with period 
, low value 
and 
. The above expression then becomes:
as 
. From this, it is obvious that the average value of the signal (
) is directly dependent on the duty cycle D.
，那麼要『 A 』又有何用？因是之故，『科學假設』 
通常是說， 
，因此才可以判定『是非對錯』的吧！！
