Sending ASCII does not guarantee this balance, as a stream of 01000000 characters, will have quite a different average 'on' level to 01111110 which is also a valid ASCII character. This system can send streams of 1 and 0's indefinitely and in any combination and the average RF level between on and off is always equal, so the AGC remains centered in its most sensitive and accurate zone. You need to investigate a coding process called Manchester Encoding.

If there are too many off's to on, then the average signal level will drift low, the AGC will follow it, and next thing data is being corrupted because it the Rx is not working at the mid-point.Ĭonsequently transmitting simple ASCII based text which you appear to be doing is fraught with danger. The Rx units do not have fancy level discriminators and rely on the signal to have equal parts above (ie =1) and below (ie =0) to have the average of the signal midway between on and off. If that frequency is strong enough the AGC dampens down the response of the Receiver and it only responds to the stronger pulses of the local signals, the digital output becomes a clean strong pulse stream. The answer is an Automatic Gain Control based on the fundamental frequency of the transmitter. The problem though is how to discriminate between random fluctuations (ie general RF noise around us which they respond to randomly) and a strong local signal with real data in it. The RF modules are generally provided with hi-gain receivers and can latch onto their tuned frequency, and produce a digital output, ie RF present = 1, RF absent =0.

So you can check the logic of the data sent and received without the vagaries of the RF connection. If you connect the output of the sending device at TTL levels (approx 0V=0, 5V=1) then the connections are at levels, that are sustained no matter what the baud rate or the 'on to off ratio'. The Rx & Tx lights only come on when there is serial comm's occurring.įrom the Arduino code sample at the sparkfun link, the Tx would transmit pretty frequently, and the Rx would not if it was not receiving anything, /*Īre you running the code on 2 different processors?Ĭould also bypass the Rf, connect Tx to Rx, Rx to Tx, Gnd to Gnd, confirm data is going across and being received, then go back to Rf.

System shock 2 transmitter code