Wireless multi sensor Humidity & Temperature system

Projects General Guidance
1

Hi..
I'm posting here get advice (help) on how to proceed in low budget and efficient way to build a Wireless multi sensor Humidity & Temperature system.

My requirements are:

  • Low cost
  • Wireless system (no cables).
  • Sensors (battery powered ,~AA batts)

Something like this :

i have put the dth11 sensor because i already used one in the past with good results and cheap but not mandatory
For the receiver i will use arduino uno with an LCD and usb connection the pc .

Main questions and worries:

What will i use for wireless ?

Options :
**1- NRF24L01 2.4GHz Wireless Transceiver Module **
What i like:

  • I read that i can use it on 6 members network
  • some libraries available.
  • Bidirectional

Don't like:
Will this mess with 2.4ghz wifi network ?

2 RF Link Transmitter - 434MHz (laipac).
What i like:

  • some libraries available (virtual wire)
  • Price

Don't like:
Don't know if i can do a network with this

My first approach for remote sensor:

  • Arduino mini pro
  • RF Link Transmitter - 434MHz
  • DTH11 sensor
  • 4 AA batts 4.8v

i will read the dth11 info and send it to the receiver identifying the sensor something like a string "SzTxx.xxHyy"
S=Sensor id
T= temp
H=hum

And i will send this information 5 in 5 minutes..

The receiver will be

  • Arduino uno
  • RF Link receiver - 434MHz (virtual wire)
  • lcd

I will be listening to radio and when a message arrives i will check the sensor who send it and then print to the serial console and to the lcd...

makes sense ?

will these communication work ?
how to reduce the sensor costs/equipment ? i don't need intelligence on the sensors some dumb wireless that has an ADC or way to read temp/hum sensor and pass the raw values to the receiver will be ok...

this will split in 3 floors :

floor 2:
2 sensors

floor1
1 sensor

floor 0
2 sensors

the distance will be lets say 20meters maximum between sensor module and receiver.

I would like to keep the sensors at 10€ but i'm already off

Arduino Pro Mini 168 - 5V/16MHz - 10€
Dth11 Sensor - 2€
Rf Link pair - 4€
batts 5€

So i'm at least a ~20€ per sensor.. i would need 5 making 100€...

Suggestions, new ideas, comments please (before i start to waste money ;)..

Regards..

2

I've gone with the NRF24L01 approach and it is working well. The spec says the system supports up to six input radio channels at each device i.e. each Arduino can listen to input from up to six other Arduinos at the same time, and send to them.

I don't know how the radio protocol works, because there is clearly some sort of handshake going on within the radio level, but I've found that in practice it is possible to have multiple senders all sending on the same channel. Hence it seems possible to have more than six remote Arduinos, as long as they don't need to transmit at the same time and as long as they are 'send only'.

Bidirectional comms would almost certainly require a separate channel for each remote Arduino though.

NRF24L01+ transceivers are available extremely cheaply on ebay, if you don't mind waiting for them to be posted from China.

3

Just ordered 2 nrf2401+ to start testing it and 2 dth11.

if the sensors won't need logical ack they always be sending not receiving, if i have to implement some kind of logic on arduino side to ack that i received then maybe they can also receive info...

I want them to work in sleep mode and lets and send the readings 5 in 5 minutes..

i can't control if they will send at the same time, i hope that the radio part take care of that or else i will have to to do a "pull " from the receiver to all the sensors that will not allow me to have them in sleep....
so i prefer the push from the sensors to the receiver..

thanks

4

For reading the DHT11 this lib might be usefull - Arduino Playground - DHTLib -

Note: the DHT22 has more digits for temperature.
Note: check the datasheets for the delay between readings to prevent "bad" readings.

5

fca:
i can't control if they will send at the same time, i hope that the radio part take care of that or else i will have to to do a "pull " from the receiver to all the sensors that will not allow me to have them in sleep....

You could put to sleep the sensors for 5 minutes after answering the receiver. After that time, just awake them and wait for receiver to ask. Reciever would never ask while they are sleeping as it waits for 5 minutes after the last sensor answers, and the sensors "go to bed" as soon as they answer, so if you always ask in the same order you could never ask while a sensor is waiting.

The alghorithm should something like that. Could be better if you wait for a while if a sensor doesn't answers and maybe some other trick to sync receiver and sensors.

Good luck

6

Hi there i just start to receiving the parts for the first sensor prototype..
I'm now after power supply..
I have several Lithium Polymer 454261A8T with a bq2060 protection circuit I'm thinking on use them on the sensors..

Advantages :
1º i can talk to the battery by i2c an know status and remaining time , etc,etc.. so i can know when is time ro change the batt .
2º Small size
3º price (i already have them)..

i will post a photo of the all circuit with battery, my batteries are sony, not varta..

batt specs (close)

batt controler chip specs