RF Transmitter/Reciver

[Fredrick]

Can i use one transmitter to send the temperature from an DS18S20 to 3 recivers?

[mackrackit]

Yep, as long as they are all the same frequency.

[Fredrick]

Whats the diffrents between 315MHz, 418MHz, 433MHz modul? Only the MHz or has it to do whit other things?

To write a program to those modules i use SEROUT and just send a text and recive it whit SERIN?

[Acetronics2]

Hi,

The answer is quite simple :

Some frequencies are allowed in your country ... and some not.

Think to verify it before buying ...

Alain

[Fredrick]

Ok, my remote controll to my car is 433MHz so i asume that that is what i should buy.

[mackrackit]

The frequency is the only difference.

Here is a thread with some sample code
http://www.picbasic.co.uk/forum/show...0584#post50584

[dhouston]

The frequency and the allowed output power differ depending on the region or country. Europe uses 433.92MHz and allows far more power than is allowed in N. America.

[Fredrick]

Have just placed an order for 2 433.9 MHz transmitters and 2 recivers..

The parallax manual says upp to 500+ feets and LINX says upp to 3000 Feets, what is the actul range?
Can i make parallax 433.9 MHz transmitter to send whit more power?

[Fredrick]

Have looked at the datasheet for the TXM-433-LR and find an intressting point.

USING LADJ
The Level Adjust (LADJ) line allows the transmitter’s output power to be easily
adjusted for range control, lower power consumption, or to meet legal
requirements. This is done by placing a resistor between VCC and LADJ. The
value of the resistor determines the output power level. When LADJ is connected
to VCC, the output power and current consumption will be at its maximum. Figure
4 on Page 3 shows a graph of the output power vs. LADJ resistance.
This line is very useful during FCC testing to compensate for antenna gain or
other product-specific issues that may cause the output power to exceed legal
limits. A variable resistor can be temporarily used so that the test lab can
precisely adjust the output power to the maximum level allowed by law. The
variable resistor’s value can be noted and a fixed resistor substituted for final
testing. Even in designs where attenuation is not anticipated, it is a good idea to
place a resistor pad connected to LADJ and VCC so that it can be used if needed.
For more sophisticated designs, LADJ can be also controlled by a DAC or digital
potentiometer to allow precise and digitally variable output power control.

It´s look like i can easy modifie my RF module to work whit the range of 3000 feet or (900 meters) by removing or replace the resitor R5 (se Picture), and i think it´s still legal i sweden to transmit at this ranges on the private 433.92 MHz band.

http://www.parallax.com/Portals/0/Im...79/27980-L.jpg