Need a cheap binary AM transmitting circuit

[hxtasy]

Need a cheap "binary" AM transmitting circuit

I'm posting this in a forum because I'm not really sure what to search for online. I need a circuit that transmits a one or a zero, basically I have a sensor and i want it to turn something on or off remotely. I was thinking about using an AM oscillator crystal, the range does not have to be far, like 20 feet. Most circuits I looked at were transmitting a frequency, carried on the AM - so I'm not really sure how I would just transmit an on/off state. I guess i could transmit like <1kHz for off and >2kHz for on, but I'm sure there is an extremely easier way to do this.

Any Ideas?

 

[berkeman]

I'm posting this in a forum because I'm not really sure what to search for online. I need a circuit that transmits a one or a zero, basically I have a sensor and i want it to turn something on or off remotely. I was thinking about using an AM oscillator crystal, the range does not have to be far, like 20 feet. Most circuits I looked at were transmitting a frequency, carried on the AM - so I'm not really sure how I would just transmit an on/off state. I guess i could transmit like <1kHz for off and >2kHz for on, but I'm sure there is an extremely easier way to do this.

Any Ideas?

I googled RF Remote Control Kits, and got lots of good hits. Here's one of the first:

http://store.qkits.com/category.cfm/RC

It's not a good idea for you to try to make your own RF transmitter -- too easy to violate FCC rules, and cause interference with other radio receivers (like Police / Fire / EMS radios). Using a kit should give you a transmitter that meets the TX rules.

 

[vk6kro]

I have seen modules for 433.9 MHz that would be suitable. You get a pair of one transmitter and one receiver for about $20.
This is a legal frequency for low powered low interference devices in some countries (although it was swiped from the 432 MHz ham band!).

It would be better to have a signal present all the time because you could get noise when the transmitter is not turned on.

If you wanted to make it bulletproof, you could have modem chips at each end.
One is the TCM3105 which was used for Packet Radio and may still be available.
These chips give specific audio frequencies out for digital input and produce digital output from the same audio frequencies.
Might be an overkill if you only want simple signalling..