使用 Raspberry Pi 开发板进行批量更新
此示例展示如何使用运行 Python 2.7 的连接 Wi-Fi 的 Raspberry Pi 板收集数据。您可以每 15 秒连续收集一次 CPU 温度和 CPU 利用率，并每 2 分钟批量更新一次 ThingSpeak 通道。本示例使用 Bulk-Write JSON Data API 批量收集数据并将其发送到 ThingSpeak 通道。通过使用批量更新，您可以减少设备的功耗。由于 Raspberry Pi 开发板没有配备实时时钟，因此您可以使用相对时间戳来批量更新消息。
设置
按照在新通道中收集数据所示创建一个通道。
代码
1) 导入脚本必要的库。
import json import time import os import psutil import requests
2) 定义跟踪上次连接时间和上次更新时间的全局变量。定义更新数据的时间间隔，并将数据发布到 ThingSpeak。
last_connection_time = time.time() # Track the last connection time last_update_time = time.time() # Track the last update time posting_interval = 120 # Post data once every 2 minutes update_interval = 15 # Update once every 15 seconds
3) 定义您的 ThingSpeak 写入 API 密钥和通道 ID 设置，以及 ThingSpeak 服务器设置。
write_api_key = "YOUR-CHANNEL-WRITEAPIKEY" # Replace YOUR-CHANNEL-write_api_key with your channel write API key channel_ID = "YOUR-CHANNELID" # Replace YOUR-channel_ID with your channel ID url = "https://api.thingspeak.com/channels/" + channel_ID + "/bulk_update.json" # ThingSpeak server settings message_buffer = []
4) 定义函数 httpRequest，向 ThingSpeak 发送数据，并打印服务器的响应代码。响应代码 202 表示服务器已经接受请求并将处理它。
def httpRequest():
# Function to send the POST request to ThingSpeak channel for bulk update.
global message_buffer
bulk_data = json.dumps({'write_api_key':write_api_key,'updates':message_buffer}) # Format the json data buffer
request_headers = {"User-Agent":"mw.doc.bulk-update (Raspberry Pi)","Content-Type":"application/json","Content-Length":str(len(bulk_data))}
# Make the request to ThingSpeak
try:
print(request_headers)
response = requests.post(url,headers=request_headers,data=bulk_data)
print (response) # A 202 indicates that the server has accepted the request
except e:
print(e.code) # Print the error code
message_buffer = [] # Reinitialize the message buffer
global last_connection_time
last_connection_time = time.time() # Update the connection time
5) 定义函数 getData，以摄氏度为单位返回 CPU 温度以及以百分比为单位的 CPU 利用率。
def getData():
# Function that returns the CPU temperature and percentage of CPU utilization
cmd = '/opt/vc/bin/vcgencmd measure_temp'
process = os.popen(cmd).readline().strip()
cpu_temp = process.split('=')[1].split("'")[0]
cpu_usage = psutil.cpu_percent(interval=2)
return cpu_temp,cpu_usage
6) 定义函数 updatesJson 每 15 秒持续更新消息缓冲区。
def updatesJson():
# Function to update the message buffer every 15 seconds with data.
# And then call the httpRequest function every 2 minutes.
# This examples uses the relative timestamp as it uses the "delta_t" parameter.
# If your device has a real-time clock, you can also provide the absolute timestamp
# using the "created_at" parameter.
global last_update_time
message = {}
message['delta_t'] = int(round(time.time() - last_update_time))
Temp,Usage = getData()
message['field1'] = Temp
message['field2'] = Usage
global message_buffer
message_buffer.append(message)
# If posting interval time has crossed 2 minutes update the ThingSpeak channel with your data
if time.time() - last_connection_time >= posting_interval:
httpRequest()
last_update_time = time.time()
7) 运行无限循环，每 15 秒连续调用函数 updatesJson。
if __name__ == "__main__": # To ensure that this is run directly and does not run when imported
while True:
# If update interval time has crossed 15 seconds update the message buffer with data
if time.time() - last_update_time >= update_interval:
updatesJson()
