Offhand:
- AC modulate (using a variety of encodings). A simple example would be keyed tones, one oscillator and one decoder for each signal.
- Make a simple DAC: combine the pulses, with binary weighted resistors, into a summing amp. Receive with comparators. As miso said, Gray code helps here.
- Do it in serial, but make it a real hack job, way fewer transistors than a uC. Example: send a long pulse to reset the receiver (use a timer to measure the pulse width). Then send a series of pulses, which are gated into a counter. Counter increments to whatever bit pattern is required (you might use a "one-hot" shift register since your signals are one-at-a-time). When counting is done, another long pulse (of opposite polarity or different time length) can be used to clock a second register, buffering the data, or to enable the outputs for the pulse.
Regular (asynchronous) serial can be used, too, but you need more accurate timing. Over a couple of bits, it's probably not a problem to use an RC oscillator for the job. In which case, you could use the start bit as an enable to start the timer, which keeps ticking for a certain number of cycles (an analog counter can be made with a couple of transistors, by the way, so you don't have to wire up a counter and gates to do it).
Note these will work with a single conductor (and ground) transmission line, and can be suitable for any combination of signal lines, not just one-at-a-time (you can usually squeeze them together with an N-to-2^N decoder, as you noted).
Tim
--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com
"Pimpom" wrote in message
news:ked3up$p09$1@news.albasani.net...
> Scheme: I have these three different sources of irregular
> low-repetition-rate pulses, no two occurring at the same time, and I
> want to send them over a long 2-core shielded cable. I suppose they
> could be sent as serial data, but my knowledge of MCUs is limited and
> dedicated encoder-decoder pair ICs introduce uncertainty periods of tens
> of milliseconds. Such periods can be tolerated but undesireable if they
> can be avoided.
>
> I thought I'd found a clever solution by encoding the signals to 01, 10
> and 11 signals and decoding them at the receiving end with a 2-to-4 line
> decoder like the CD4555. Then it occurred to me that slight differences
> in wire length and cable and stray capacitances could introduce
> different time delays between the two lines and cause decoding errors.
> The 11 signal in particular could be mistaken for a momentary 01 or 10
> pulse. Subsequent controlled stages will not be adversely affected by an
> erronous sub-millisecond 01 or 10 pulse at the rising edge of the 11
> signal, but the falling edge could cause problems.
>
> Proposed solution: Have the decoded 11 pulse at the receiver trigger a
> monostable. The 11 pulse is a reset signal and will override the effect
> of any spurious 01 or 10 signal during the mono period..
>
> Have I missed anything?
>