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Topic: Help us get terms right- waves- DCDW (Read 1 time) previous topic - next topic


Jan 12, 2011, 04:13 pm Last Edit: Jan 12, 2011, 04:19 pm by tkbyd Reason: 1
Sorry... please infer a "please" in that thread title? (Speaking of which, if anyone can tell me how the person who started a thread can modify the title of a thread after there's been a reply, a PM on the subject would be welcome!)

In the growing documentation for the Dirt Cheap Dumb Wireless module, I have attempted to set out the correct meaning of a bunch of terms connected to datastreams consisting of "on"s and "off"s.

If you would be willing to cast a critical eye over my Dr Johnson efforts, and bring errors to my attention, I would be very grateful, and you would be helping move the DCDW project forward.

Definitions at...



Jan 13, 2011, 05:58 am Last Edit: Jan 13, 2011, 06:02 am by AltairLabs Reason: 1
Nice work !

1) The "xxx" shows the output from the receive module when the transmit module is not switched on. "Inter-packet dead interval"? NEEDS A MORE CONCISE NAME! During such periods, unless another DCDW unit nearby is transmitting, the output of the receiver will be undefined, and, shortly (define more closely?) after tx shuts down, the output from rx will start swinging (sharply?) from 0 to 1 and back again, randomly. (Nature of this random signal?) Note that if a DCDW module is connected directly to the monitoring computer, no RF link, for debugging or other reason, then during "inter-packet dead interval" state of input will be determined by the passive components, in particular a likely pull up (or pull down) resistor.

I'll have a go at this one and what we have learned about these

For name of what happens between data packets how about "message gap" or just "gap".  

The gaps are full of Boltzman's thermal noise, kTB, as shaped by the RX filter and detector. The filter passes about 15 kHz worth of Boltzman and the detector thresholds itself just below the average.  So you see 0v out the data pin with random pulses to 5v somewhat less than 50% of the time. The analog nature starts to show, as the "data" pin often rises above 0v and wanders about then goes back to 0v without ever getting anywhere near +5v.  So these little beasties put out quite a complex and disorderly signal as "RX Data" when "nothing is happening".

Using these with serial USART would produce sporadic random characters when the TX is turned off.  But they so darn CHEAP we at DCDW love them and forgive them for having no hardware squelch.  Fortunately software squelch is working out quite well!

One final note, on mine the RX Data pin seems weak, not able to overcome even a modest resistor, have to disable Arduino pull-up to read data. Anybody else observe this? Need to open my only "spare" and see if acts the same or maybe 1st one is damaged.

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