ESP8266 Community Forum

- Sat Jul 30, 2016 5:52 am #51766 I am playing around with a mobile ESP12-based Si7021 temperature/humidity sensor.
As it runs on LiIon battery, it deepsleeps for about 5 minutes, resets, reads out the sensor, posts the data to my local python cgi script and goes to sleep again.

Weird thing is that upon startup, this takes about 2.4-2.5s. After deepsleep, this rises 500-600ms up to 3.05-3.15s. This is with optimizations in place already: Compiling the Si7021.lua module to .lc, compiling the main program and renaming it to init.lua. This reduced the time it takes about 500ms already.

I was starting with a DHT22 which works well and was the same speed without any of such optimization thanks to the firmware included module. But it's quiescent current is way too high and the values are way off, the Si7021 is by far superior.

Anyhow, I wonder why it takes half a second longer to transmit the values after the initial faster round. Does anyone have a clue? Here's the code:

Code: Select allstarttime = tmr.now()
-- setup Wifi only once after power cycle
local val = rtcmem.read32(0)
if val ~= 32767 then
  wifi.setmode(wifi.STATION)
  wifi.setphymode(wifi.PHYMODE_N)
  wifi.sta.config("<SSID>", "<password>3")
  -- save more power by using static IP instead of DHCP
  wifi.sta.setip({ip="<my ip>",netmask="255.255.255.0",gateway="<my gw ip>"})
  wifi.sta.connect()
 
  rtcmem.write32(0,32767)
end

-- read AM3220 / Si7021 on GPIO2/0 = Pin 4 / 3 -
sda_pin = 4
scl_pin = 3
si7021 = require("si7021")
si7021.init(sda_pin, scl_pin)
si7021.read(status)

wifi.sta.status()
--print(wifi.sta.getip())


-- Deep sleep time in ms (300s)
deepsleep_time = 300000

local sensor = "mobile"
local host_ip = "<receiving host ip>"

function loop()
  if wifi.sta.status() == 5 then
    -- Stop the wifi connection wait-loop
    tmr.stop(0)
   
    conn=net.createConnection(net.TCP, 0)
    conn:on("receive", function(conn, payload)
--      print(payload);
    end)
    conn:connect(80,host_ip)
    conn:on("connection", function(conn, payload)
--      print("Connected")
      -- read battery voltage
      local vbat = 5.555*(adc.read(0)/1024)
      local humi = si7021.getHumidity()
      local temp = si7021.getTemperature()
--        buf = temp.."\n"..humi.."\n"
      local my_table = {}
      my_table[#my_table + 1]="GET /send.py?sensor="
      my_table[#my_table + 1]=sensor
      my_table[#my_table + 1]="&temp="
      my_table[#my_table + 1]=string.format("%.2f",(temp/100))
      my_table[#my_table + 1]="&hum="
      my_table[#my_table + 1]=string.format("%.2f",(humi/100))
      my_table[#my_table + 1]="&vbat="
      my_table[#my_table + 1]=string.format("%.3f",vbat)
      my_table[#my_table + 1]="&time="
      my_table[#my_table + 1]=string.format("%.3f",((tmr.now() - starttime) / 1000000))
      my_table[#my_table + 1]=" HTTP/1.1\r\nHost: "
      my_table[#my_table + 1]=host_ip
      my_table[#my_table + 1]="\r\nAccept: */*\r\n"
      my_table[#my_table + 1]="User-Agent: Mozilla/4.0 (compatible; esp8266 Lua; Windows NT 5.1)\r\n\r\n"
      local my_string=table.concat(my_table)
      conn:send(my_string)
    end)
    conn:on("disconnection", function(conn, payload)
--      print('Disconnected')
      conn:close()
--      print(buf)
--      collectgarbage()
--    print("Going to deep sleep for "..(deepsleep_time/1000).." seconds")
      node.dsleep(deepsleep_time*1000)
    end)
  else
--    print("Waiting for Wifi ...")
  end
end

tmr.alarm(0, 100, 1, function() loop() end)

-- Watchdog loop, will force deep sleep if the operation somehow takes to long
tmr.alarm(1,15000,1,function() node.dsleep(deepsleep_time*1000) end)
-- eof

- Sat Jul 30, 2016 11:54 am #51779 The reality looks even worse. The ESP is active for nearly 10s until going to deep sleep. Just soldered a 2 * R500 connection to look at the power usage with the scope (click leads to bigger image):



Closer look:


Maybe going to deepsleep directly in the OnConnection event handler may help there. This is quite a waste of energy until now. :-/

- Sat Jul 30, 2016 5:30 pm #51807 Just for completeness:

Improved situation. When moving the DeepSleep call to the on:receive callback function, the ESP goes to sleep after close to 4s - at startup and after wakeup.

Further optimization are still welcome, though.

- Sun Jul 31, 2016 8:42 am #51845 Can I finally post without moderation? This is really a bit over the top, no fun to post.

In case someone else wants to speedup his lua Wifi sensor, I managed a bit more. I repeated the static IP line after the "setup wifi only once" block. This isn't clean coding, but ...

Startup time is down to 3.6s (click leads to bigger image):


But most impressive is the result after deepsleep:


Down to 1.2s from 4s awake time! The ESp measures 300-400ms from start to sending the data, by the way, which was 3s before.

Together with the 45µA quiescent current from the ESP+EEPROM, Si7021 and MCP1700 LDO this now gives me real long runtime with measuring and transmitting temperature, humidity and battery voltage every 5 minutes!