Wifi temperature / humidity sensor for under £20
Overview
So I travel a lot, and want to know what's happening in the house whilst I am abroad.I've researched and there are many solutions out there (like here or here), but mostly they are way, way over priced at over £150 EACH per unit.
I need at least 5 units, for the bathroom, kitchen, boiler room etc. so even doing it with a raspberry pi would have been pricey at around £40-50 per 'sensor' (using the DHT22 for readings), so an outlay of about £250.
What I have found is something even better. The ESP8266. This is a self contained wifi module with built in TCP/IP stack for around £3 and under the size of a 50pence piece. Whoa - cheap eh? Ok, so the issue here is that it can't do a 5v-3v logic shift nor can I be bothered to figure out the electronics to step it down and connect it to USB TTL etc.
So.... I researched a bit more and there is a board that combines the ESP8266 and the step down and the USB TTL and allows me to either publish data via a message queue or host a webserver! This is the NodeMCU
Fantastic little thing that does everything you need it to + can be powered from a micro USB connection.
Parts list
ok so the parts list (you may not need to purchase everything, as you may have some parts already)1 x NodeMCU (Amazon or ebay) - Beware of the version you get tho! Check the PCB colour and size.
1 x DHT22 temperature/humidity sensor (Amazon or ebay)
A breadboard /protoboard to prototype stuff (pimoroni) - you'll solder it onto this.
A solderless breadboard to test things work (pimoroni)
Soldering iron
Micro USB cable for connecting to a PC
some cheap micro usb charger
Wires for testing (Jumper jerky makes it easier)
Wires for permanent installation (pimoroni)
Total cost of the above is about £30 for the first unit. Cost of the 2nd unit will be about £13, 3rd unit about £13 too, so for 5 units, it's about £16 each. Not bad
Circuit diagram
Dev software
ESP software - for loading up LUAs and code
Firmware
Download the firmware
Flashing firmware
config tab
select first slot
flash on tab one
ensure the MAC addresses show. If not, then something went wron.
A green tick at the end shows success.
Modules
DHT22 from hereUpload it with esplorer from above using the 'upload' button. Then compile by clicking reload on the middle right side, then a list of modules will appear. Right click and select compile.
Code
Set the wifi access point and set NIC to DHCPprint(wifi.sta.getip())
--nil
wifi.setmode(wifi.STATION)
wifi.sta.config("SSID","password")
print(wifi.sta.getip())
--192.168.18.110
View wifi SSIDs
function listap(t)
for k,v in pairs(t) do
print(k.." : "..v)
end
end
wifi.sta.getap(listap)
onboard LED
Flash the blue LED near the USB connector
gpio.write(0,gpio.LOW)
gpio.write(0,gpio.HIGH)
GPIO LEDs
Flash an LED on GPIO pin 2
pwm.start(2)
You can change the duty cycles by checking the docs http://www.nodemcu.com/docs/
pwm.setup(2,1,10)pwm.start(2)
Reading temperature/humidity
PIN=4dht22 = require("dht22")
dht22.read(PIN)
t = dht22.getTemperature()
h = dht22.getHumidity()
humi=(h/10).."."..(h%10)
temp=(t/10).."."..(t%10)
print("Humidity: "..humi.." %")
print("Temperature: "..temp.." deg C")
dht22 = nil
package.loaded["dht22"]=nil
All together:
print(wifi.sta.getip())
gpio.mode(2,gpio.OUTPUT)
--gpio.write(2,gpio.HIGH)
--gpio.write(2,gpio.LOW)
--gpio.write(1,gpio.LOW)
gpio.write(0,gpio.LOW)
BLUE=1 -- blue LED is on GPIO 1
pwm.stop(2)
pwm.stop(1)
pwm.setup(2,1,10)
pwm.start(2)
gpio.write(0,gpio.HIGH)
sv=net.createServer(net.TCP, 2)
sv:listen(80,function(c)
c:on("receive", function(c, pl)
print(pl)
Note the above server doesn't respond to normal HTTP requests. it responds with a simple:end)
gpio.mode(BLUE,gpio.OUTPUT)
gpio.write(BLUE,gpio.HIGH)
PIN=4
dht22 = require("dht22")
dht22.read(PIN)
t = dht22.getTemperature()
h = dht22.getHumidity()
humi=(h/10).."."..(h%10)
temp=(t/10).."."..(t%10)
print("Humidity: "..humi.." %")
print("Temperature: "..temp.." deg C")
dht22 = nil
package.loaded["dht22"]=nil
c:send("H:"..humi.." ; T:"..temp.."\r\n")
c:close()
gpio.write(BLUE,gpio.LOW)
end)
H:xx ; T: xx
and disconnects after the initial connect.
You can use either curl or netcat to get the data.
It also flashes the blue LED whilst a network operation is in effect.
The white LED I've used blinks every second, to show it is working.
Dashboard
RRDtool - Create the RRD
This creates a RRD for 5 sensors, values 0 to 100 and 524160 data points (60*24*7*52) so 1 data point a minute
<?
echo "Creates blank temp graphs";
$options = array (
"--step", "60", // Use a step-size of 1 minute
"--start", "-1 day", "DS:hum1:GAUGE:100:0:100",
"DS:hum2:GAUGE:100:0:100",
"DS:hum3:GAUGE:100:0:100",
"DS:hum4:GAUGE:100:0:100",
"DS:hum5:GAUGE:100:0:100",
"RRA:AVERAGE:0.3:1:524160",
);
$ret = rrd_create("./hum.rrd", $options);
if (! $ret) {
echo "<b>Creation error: </b>".rrd_error()."\n";
}
?>
echo "Creates blank temp graphs";
$options = array (
"--step", "60", // Use a step-size of 1 minute
"--start", "-1 day", "DS:hum1:GAUGE:100:0:100",
"DS:hum2:GAUGE:100:0:100",
"DS:hum3:GAUGE:100:0:100",
"DS:hum4:GAUGE:100:0:100",
"DS:hum5:GAUGE:100:0:100",
"RRA:AVERAGE:0.3:1:524160",
);
$ret = rrd_create("./hum.rrd", $options);
if (! $ret) {
echo "<b>Creation error: </b>".rrd_error()."\n";
}
?>
