understanding multiplexing

KPierson wrote: My personal take on it, and it may just be my opinion, but multiplexing and data signals are two different concepts. Multiplexing is is a way of encoding multiple signals on one wire, usually by varying voltage (0-5vdc or 0-10vdc analog signals), by current (0-20ma or 4-20ma are commong) or by pulse widths (servo control).  In cars, generally you will only see voltage multiplexing and it's usually not 0-5vdc analog, it's usually a few precise voltages somewhere between 0 and 5vdc.  An example of this would be steering wheel buttons for radios, cruise control, air conditioning, etc.  If you push one button it will drop the voltage to 0.5vdc, another would drop it to 1.0vdc, and so on.  In the typical car scenario there are a limited number of possibilities. Data signals are different because they follow protocols (RS232, CAN, LIN, etc).  They have baud rates and have start/stop bits and data bits as well as other parameters predefined.  A data signal can transmit much more data much quicker then a typical multiplexed system.

KPierson,

Wow, awesome feedback. You obviously have an indepth understanding on the topic. So, you say here that data signals can transmit greater amounts of data than a typical multiplex system.  But, how can data signals tranmits "quicker," or at a faster rate when electrons on copper wire all travel at the same rate (appr. 66% the speed of light).  Are you saying that the data is "processed" at a faster rate?

Data and multiplexing are different as KP said, these are some sites on the data side of things!

KPierson wrote: My personal take on it, and it may just be my opinion, but multiplexing and data signals are two different concepts. Multiplexing is is a way of encoding multiple signals on one wire...

I'm too late on the admiration wagon, so I'll stay technical. Bingo! Spot on! Well put, etc etc. I was going to say "Multiplexing is is a way of encoding multiple inputs on one wire..." (or outputs). EG - 4 cameras, 1 input. Switch between the cameras. Or save cables - 4 cameras, one LONG tranmission line - switch 4 cameras successively thru the line. Then maybe switch each to their own monitor. IE - time-switch or multiplex 4 cameras thru 1 line and then de-multiplex to their 4 monitors. And that's a bad example. A common example is multiplexed displays - eg 7 segment LEDs (digits) that each require 8 connections - 7 segments and a common. Instead of a 4-digit clock having 4x8 = 32 wires to the display, why not 11 wires? IE - 7 wires that go to or though all 4 digits. Then the 4 separate common wires. Display "1" on digit #1 - turn on the 2 of 7 wires for the "1" segments, and the "common" for digit #1. Display "2" on digit #2 - turn on the 5/7 wires for "2" and the common for digit #2 (noting that common for digits #1, $3 & #4 are off!!). Etc. Similarly for inputs - a common modern example being several analog inputs like coolant temp, oil pressure, oil temp, voltage etc into a electronic or engine management systems (EMS). Because Analog to Digital Converters (ADCs) are expensive or a pain to manufacture, and because most analog signals are very slow compared to uPCs (micro-Processors) etc, they often use the same ADC for all analog inputs - ie, multiplex the inputs aka channels. I see multiplexing as a "mechanical" means of sharing a pipe. It can be called time-sharing etc. It is not necessarily digital per se, just the sequential time sharing of different input or outputs over the same line(s). "Data" is different. (Assuming "data" to be as in digital communications - computer speak etc.) Data is the encoding through the pipe or line from the inputs etc. Whether your sensors (temp, pressure etc) are multiplexed is irrelevant. You somehow collect their values, ADC them to a digital value comprising "bits" (ones & zeros), and send that "data" down the line to the <whatever> that decodes these 1's & 0's. EG - binary 111 = 7; 101 = 5 etc. Bitrate is how fast you send the data. High bandwidth is required for fast data because "speed is bandwidth" - but that gets a bit complicated. (Nyquist Theorem springs to mind.) I've seen a nice diagram somewhere that shows a multiplexed system output (maybe a screen or 7 segment displays?) as parallel things and a rotating switch underneath that selects each one at a time. The input is other parallel things (temp, oil-P etc, or time-digits) with a similar selector switch. There is a link between the two switches showing that they are synchronised. Not that I looked a the previous mentioned links! Is it here that I should add that there is no such thing as digital transmission? Nah - maybe not.

IOW analog encoding rather than time multiplexing. Still the same "sharing a single line between multiple signals" concept. (And no different to "digital transmission" lol!) My old Sony auto-reverse twin cassette (from 1980!) used that system for its remote. You unhooked its front panel and plugged in a 3.5mm stereo-plugged cable. Upon investigation () I found it multiplexed its 8 or so fwd, rwd, play, rec, etc buttons using different resistor values. It was cute for the time (30 years ago), but those systems were replaced by their easier manufactured digital encoders.    I would have thought a preference for non-analog systems in cars given the harsh electrical environment etc, as well as in general these days thanks to our lovely GSM system (hey - I refused GSM and used CDMA, but the bricks shut down our CDMA! ).