Does RF transmitter transmit all the time?

Using Arduino Networking, Protocols, and Devices
1

Hi,

I want to connect two arduino boards with RF link. What I don't want is that the transmitter will transmit all the time. I just want it to transmit when pushing a button for example. Does the RF transmitter goes to idle by itself or I need to take care of it?

Thx

2

Which RF transmitter?

3

Example

http://www.ebay.com/itm/1pcs-433Mhz-RF-transmitter-and-receiver-kit-for-Arduino-project-/261100136245?pt=LH_DefaultDomain_0&hash=item3ccac7e735

4

Those will transmit constantly, but only a carrier frequency. There will only be data overlaid on that when you send data.

5

Thx

So what is the simple way to stop transmission and enable it only before I want to transmit something?

Eyal

6

So what is the simple way to stop transmission and enable it only before I want to transmit something?

Why do you want to?

You could see how much power they draw. If it is less that 20mA, you could power the radio from a digital pin, and turn that pin on and off as the need to transmit data arises/goes away.

There will only be data available to be read when the receiver receives data, so turning the sending radio off won't have any affect on the receiver.

7

I can't see the e-bay link - is that for parts like these?

http://www.robotshop.com/search/search.aspx?locale=en_us&keywords=434 mhz

http://www.robotshop.com/433mhz-transmitter-receiver-pair.html

http://www.robotshop.com/433mhz-high-sensitivity-transmitter-receiver-pair-rxa33.html

http://www.robotshop.com/433mhz-high-sensitivity-transmitter-receiver-pair-rxa30.html

They work well with virtual wire to ensure that the receiver only passes on valid data:

"
RF ASK Transmitter/Reciever Example
//
// This code depends on the VirtualWire Library for Arduino and is
// based on the example code provided by Mike McCauley (mikem@open.com.au)
// See VirtualWire.h for detailed API docs.
//
// This example shows how to use the VirtualWire library to send and receive
// simple messages and use them to control digital I/O pins. Buttons are
// connected to the transmitting Arduino on pins 8-11 (to ground, internal 20k
// pull-up resistors are set in the code) and in the same fashion,
// LEDs are connected to the recieving Arduino on pins 8-11. When a button is
// pressed on the transmitter, the corresponding LED will light on the reciever.
"

8

The ebay page says the transmitter does "Modulation mode: ASK /OOK".
In order to do OOK there would have to be a way of keying the transmitter on and off - n'est-ce pas?
However, the "documentation" is sparse at best, so that might be wrong.

Pete

9

ASK simply means that the transmitter is on (transmitting) when the data pin is high, and not transmitting when its low.
Which is why there needs to be some kind of signal processing of the data going to the transmitter, so that a continuous string
of logical 0 can never be sent, otherwise the transmitter would never transmit.
Manchester coding is used, which fixes the problem.

10

Just opened the e-bay link - maybe a good price in 2 days, and delivery in 2 1/2 weeks to a month!
I'll be 3 projects on by then - but, uh, go e-bay!

"Delivery:Estimated between Tue. Oct. 9 and Mon. Oct. 22"