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Sending Data Using Cheap RF Modules

Wireless is easier today than ever, with many standards to choose from. But you don’t need anything elaborate if you simply want to cut the cord. A few years back, [Roman Black] experimented with the cheap RF modules you can find on auction sites and from surplus electronics vendors for only a few dollars, and wrote up his findings. They’re well worth a look.

Sending Data Using Cheap RF Modules

Sending Data Using Cheap RF Modules

These modules have pins for power and antenna, transmit input (TX) for the transmitter, and receiver output (RX) for the receiver. All the TX does is turn the carrier on and off and the RX output reports the carrier status. [Roman] first used 50% duty cycle square waves to characterize how well the RX followed the TX. Below 1 kHz the match was good. At higher frequencies the RX couldn’t maintain the 50% carrier on. He found that sending 1200 bps from a USART just worked under good conditions — resulting in 83 bytes per second.

Changing up to a long-short, pulse-period protocol, where a 1 and 0 are sent for 150 and 100 usec respectively, got him much better results. He maxed out at a throughput of around 800 bytes per second.

This is an interesting experiment which shows that the protocol used on the media, in this case simple continuous wave RF, has a large effect on the transmission of data. [Roman] attained distances of 20 meters through walls which is a good distance with cheap hardware. Are there even better protocols out there?

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