433.92 MHz ASK transceivers and data rate / protocol

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1

Hi All...

I have been looking at 433.92 MHz receivers and transmitters commonly used in remote control devices and trying to understand how they work. I'm wondering if these devices use a standard bit rate and protocol? I have been searching but not found much. I'm thinking these must be very simple devices since I see even at Spark Fun they are very inexpensive.

If they are not all the same, is there a receiver that is generic, so that it could receive any protocol? That is, leave the protocol decoding to the software?

Thanks very much!

2

Those units do not have a protocol. The transmitter is on if the DATA pin is high. Furthermore the receivers have automatic gain control and will output random noise when there is no signal.

For communications you need software that implements an error checking protocol, like VirtualWire (easiest to use) or RadioHead.

3

"If they are not all the same, is there a receiver that is generic, so that it could receive any protocol? That is, leave the protocol decoding to the software?"
Yes. Can write some code to try a bunch of speeds (4800, 9600, 19200, etc) & formats (8N1, etc) and see if anything valid looking comes out.
Nice thing with VirtualWire (now part of Radiohead as RH_ASK) is that it sends out a training preamble for the receiver to get in sync with the transmitter's speed, and does Manchester Encoding to create a nice stream of 0s/1s for the data to be recovered from.
http://www.airspayce.com/mikem/arduino/RadioHead/

4

Thanks very much guys! That's good news and bad. Good in that I guess I can use any hardware, bad in that I'll have some reverse engineering work to do. I'm trying to build a receiver for remote device and all I know about it is that it's 433.92MHz ASK. I guess the protocol analyzer and my new O Scope will come in handy.

Is there a particular receiver people have had good luck with?

Hi Crossroads, nice to see you again! Thanks for the reference to the library!

5

The data rate is very low with those devices, and you can use audio signal processing (PC and sound card) to reverse engineer an unknown protocol.

See this example. Interface with Remote Power Sockets – Final Version « RAYSHOBBY.NET

6

jremington:
The data rate is very low with those devices, and you can use audio signal processing (PC and sound card) to reverse engineer an unknown protocol.

See this example. Interface with Remote Power Sockets – Final Version « RAYSHOBBY.NET

Very cool, thanks! And that RF Toy things is pretty cool too, had to have one of those!

7

Rather than doing all the work from scratch.. why not look at this project:
RFLink Gateway

Fully working and low cost solution.. you only need an Arduino Mega and a decent 433mhz receiver/transmitter..
firmware is free and already supports a few dozen of protocols.. might even support your set.