clock, data, and power on same line?

What I mean by this is that I have never seen any mention of something like this(although I think I do recall a 1-wire protocol somewhere but don't remember much). I do know that you can encode a clock with data(I think its manchester encoding?) but wonder why not move to the next "logical" step and add power. (I know its possible but it seems rarely used)

I imagine, say, if I have some speakers that need power for something(say some lights or maybe an active filter) but instead of running an extra wire for power(and I'll probably need one for ground) why I couldn't just run the power over the same analog audio lines.

Since the power is DC I could just use a cap to drain the power into and another to block DC for the audio part? (of course this is for analog stuff but I figure the same could be applied to digital)

I do realize that noise would probably become a much larger issue but I'm sure there are other things and such... which is why I ask.

Thanks guys. I'll look into it some more later now that I know it works and its actually used.

Jon

yes. just modulate the line and keep the level up to where the device will not suffer for it's rail supply. isolation with something like a diode and cap will help maintain the rail line to the device while the device can modulate it.

Of cours just because it *can* be done doesn't mean it *should* be done. A few more connections can make things a lot better.

Best regards, Spehro Pefhany

Not so in the case of the Dallas/Maxim 1-Wire iButton Products. Perfect example of how a 1-Wire interface can be used to make a unique and very effective product.

I just put a 1-Wire ID chip onto a whole bunch of boards that go into making up a product, and the ability to program the chip with info though a single wire interface while the board is un-powered is very flexible indeed. Then when the product powers up it can interrogate each board and know what boards are plugged in, what revision they are etc, and can then auto-configure itself accordingly. And it only takes a single wire which is great for retrofitting into existing designs.

Dave.

And I just yanked a DS1821 digital thermometer from a design cos it costs $12! Ive replaced it with a smt thermistor, a resistor and a capacitor, total cost $0.20. Funnily enough the IO pin it was connected to was also an ADC input.....

Cheers Terry

Welcome to the principle of horses for courses.

My $30 ThermoChron iButton is worth every cent when I can attach it to my shoelaces or harness to measure water and air temp when I go canyoning, or put them throughout my house or inside a product cabinet to log thermal profiles.

Can't use your 20 cent solution on a sole remaining I/O pin that doesn't happen to have an ADC input. And of course the DS1821 can also be used standalone when your product is too busy doing other things or went to sleep or something. Want to add some more sensors to the your only remaining I/O pin? - oops. You could of course add a $.50 PIC in that case if you were counting your pennies.

That's why there is a product for every purpose.

BTW, you were getting ripped off, the DS1821 is only $6.31 at Digikey.

Dave.

indeed. the original decision to use this part (not, of course, mine) was downright daft.

nice!

yes, you just need to think harder (and maybe spend another $0.10)

I suspect the "purpose" of the DS1821 is to allow softweare people to hook temperature sensors to micros without having to do any electrical engineering. Hell, I could use a 100nF Z5U cap to sense temperature here, I have a micro......

I built 5 prototypes of the rev 3 circuit, so didnt really care too much about the pricing; my BOM is being quoted as we speak (?!) but US$6.31 is about NZ$10, so its still more expensive than my large SCRs.

Cheers Terry

It is done. Model train buffs have a system called DCC, which uses a switched clock, the edge separation defining 1s and 0s. Communication in the reverse direction is by current loading. It's a bit slow and clunky, but it works.

Why the gratuitous razz?

Paul Burke

On a sunny day (Tue, 21 Aug 2007 19:14:45 -0500) it happened "Jon Slaughter" wrote in :

Sure it can be done, using different frequencies is one way. But the extra circuits needed are more complex then 2 extra copper wires.

The new PoE ethernet-cable-powered network devices are going to be pretty convenient.

The new PoE ethernet-cable-powered network devices are going to be pretty convenient.

Devil is always in the details. There are many examples of it being done, and being done for at least 70 or 80 years.

I actually like the old Westinghouse SCADA equipment that used 807's to put the carrier onto the power lines. I saw it being deinstalled as recently as ten years ago.

Tim.

Back in the days of ON TV (over-the-air subscription TV for you youngsters)...

Being at ~450MHz (IIRC) it was line-of-sight, and my house was in the shadow of Mummy Mountain.

But 150' to the west in my back yard it wasn't.

So I put a helical antenna (around 8" diameter by 6' long) up in a Mesquite tree, along with a UHF tuner enclosed in a ABS housing, so I could send IF at ~45MHz back to the house, rather than lose it all at

Power was 18-24V on the coax, regulated down to 12V for the tuner. The

Of course there were appropriate LC's at each end to separate signal from power.

So you can do anything with 1-wire if you set your mind to it ;-)

...Jim Thompson

It's already being done in a big way.

A DS1 rate (1.544 Mbit/s) signal (the data) uses the Alternate Mark Inversion (AMI) line-code (which can be modified by B8ZS, (binary 8 zero suppression). The data signal is used as the timing reference to sync a clock in the receiver. When the DS1 signal is transported on cable, DC voltage is transported on the simplex of the line transformers.

Data at 2.4, 4.8, 9.6, 19.2, 56, and 64 kbit/s are transported similarly, but use different codes for long binary zero strings.

If this sounds usable for you, you should get lots of good info if you google for Channel Service Unit, and Data Service Unit. The latter is because modern DSUs also contain the CSU functionality. (oops! Channel Service Unit and Data Service Unit).

Jim Thompson wrote in news: snipped-for-privacy@4ax.com:

I have an old 70 Mhz IF analog satellite receiver that uses that principal. Most others of that era had a separate power circuit. Tuning voltage was sent down the IF coax.

Of course, satellite now does something similar, but with the voltage powering the dish electronics, and sending polatiry adn satellite switching signals down the coax used to send the IF back (using fixed frequency LOs).

Just last month my employer installed a major SCADA-controlled frequency conversion system for AmTrak (I wasn't the engineer on that one; he was in the next cubicle). Sometimes old is good. :)

Power over coax is common for active GPS antennas.

snipped-for-privacy@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote in news:XNadnSQwGeXxs1DbnZ2dnUVZ snipped-for-privacy@megapath.net:

A lot of antennas and antenna mounted amplifiers do. Yes, especially microwave stuff.