Wireless temperature measurement

[DrWhoF]

adf7020 picaxe

I need to measure temperature about 50m apart. Temperature range is 10C to 80C and accuaracy 0.5C.
At receiver end I need to send the result to PC's serial port.
I can't have cables and there is no power point.
Any advices about temperature sensor, ADC and wireless Tx are welcome.

 

[IanP]

ds18b20 sensor picaxe08m

I think you are already familiar with PICAXE microcontrollers, so cutting story short, yo can do this:
At the "transmitter" endyou can use PICAXE-08M as microcontroller, DS18B20 as temperature sensor and "el cheapo" 433MHz transmtter module (plenty of inf on them in this Forum) ..
At the receiver end the same PICAXE-08M can be employed as microcntroller with matching "el cheapo" 433MHz receiver module ..
As PICAXE-08M has already build-in RS-232 port (2 resitors and 3 wires: Rx, Tx and GND) that part is already done ..

Power for the transmitter can be fed from3 x AA batteries (can be lithum, NiCad ..) that will depend on how often the temperature reading has to be aquired and sent ..

Softwarerwise, the code for transmitter can be <10 lines long as PICAXE-08M has special command to read the DS18B20 temperature sensor ( readtemp pin, register ), so can be the code for the receiver: read data when it arives from 433MHz module and send data through the serial port:

RX:
serin, pin, bla, bla, bla ; wait for data from RF module
sertxd (#register, " ") ; send data trough the RS-232 Tx pin
goto RX


Regards,
IanP

 

[alienay]

I THINK THE OPTIC FIBER IS GOOD IDEAL

 

[rat_race]

you will surely find good information about measuring temperatures in the following book which you'll find in rapidshare.. :

Newnes Interfacing Companion by fischer cripps

 

[rupeshbartunia]

Use MAX6662 (1.37$ ) chip or LM92CIM for temperature measument .It havig 12 bit output and SPI interface .Interface sensor chip with Nordic Semiconductor RF Chip nRF9E5 (4$) ,which works on 868/915 MHZ ISM band with maximum distance 50m .This RF chip having in build 8051 core inside so you can easly interface with PC serial port .

 

[DrWhoF]

Thank you guys for your responses.
I need something simple and inexpensive.

IanP. Can you suggest circuit for transmitter and receiver.
I already have PICAXE-08 and I can get DS18B20.

 

[IanP]

Below is the transmitter circuit ..
Please note that the RS-232 Rx and Tx terminals are used to program the PICAXE ..

Regards,
IanP

 

[IanP]

And here is the receiver ..

Regards,
IanP

 

[DrWhoF]

Thanks, IanP.
Can you suggest software for transmitter and receiver.
I need to take readings every >1minute.

 

[IanP]

Here is an example of a code that you can use for transmitter:

TX_Loop:
 high 2
 wait 1
 readtemp 1, b1
 low 2
 serout 4,n300,(85,85,85,85,"123",b1)
 sleep 25
 goto TX_Loop

This code will:
- supply power to the DS18B20 at OUT 2 ..
- read temperature in °C ..
- turn off the DS18B20 ..
- send out data through OUT 4
- go to sleep for ≈ 60 seconds
and repeat this sequence all over again ..

Regards,
IanP

 

[IanP]

And here is the code for the receiver:

Rx_Loop:
  serin 1,n300,("123"),b1
  sertxd (#b1, " ")
  goto Rx_Loop

This code will:
- wait for data string from INPUT 1, write temperature to register b1 after the sequence"123" is received ..
- send the value of b1 through the RS-232 Tx pin, followed by a space ( " ") ..
- and do it all over again ..

Regards,
IanP

 

[ilamseeker]

ommmm

 

[PaulHolland]

Hi Use an ADF7021 type of transceiver !. Why. It has a buildin Temperature sensor that can be read-out digitally .

Regards,

Paul.

 

[DrWhoF]

IanP: can you explain lines:

serout 4,n300,(85,85,85,85,"123",b1)

serin 1,n300,("123"),b1

 

[IanP]

serout 4,n300,(85,85,85,85,"123",b1)

4 = OUTPUT 4
n300 = 300bps
85 = 01010101 - wakeup sequence
"123"= string to decipher, followed by usable data

serin 1,n300,("123"),b1

1 = INPUT 1
n300 = 300bps
"123" = as above ..

Regards,
IanP

 

[DrWhoF]

Thank you for explanations.
I have one more question: can you suggest size and shape of antennas.

 

[PaulHolland]

Hi, If you use a ADF7020 from Analog devices with a buildin temperature sensor you can use a simple wire antenna. Wire should be 7 cm long (3 inch). This is more than you need for a 50 meter range.

ADF7020 is very easy to use and low-cost !.

regards,

Paul.

PS: No affiliation with Analog devices in any way!)

 

[IanP]

For 434MHz an antenna can be build of a piece of welding (or copper) wire: 1.2-1.5mm in diameter and 6 1/2 " (or 165mm) long .. this will be 1/4λ antenna ..

Regards,
IanP

 

[DrWhoF]

Paul, thank you very much for your suggestions but I have easy access to components which IanP proposed.
IanP, is it possible to use smaller antenna.
Once again thank you very much.

 

[IanP]

Of course it is possible to use shorter antenna ..
The only difference will be the range: with 1/4λ whip the range will be at its maximum (≈100-200m), if you shorten it you can expect also shorter range ..
For 50m, as you intended to use it, you might be OK with just a short piece of wire - possibly as short as 50mm ..
Other option is to use the whole length (165mm) and coil it so the overal size will come significantly down .. in the latter case you will need to experiment a little bit ..

Regards,
IanP