Circuit Common?

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Sparky Williams
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Circuit Common?

Post by Sparky Williams » Tue Dec 30, 2003 7:06 pm

The instructions for a circuit I'm planning to build say to connect the negative side of the power supply to "circuit common." Is "circuit common" ground?

Mike
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Re: Circuit Common?

Post by Mike » Tue Dec 30, 2003 7:42 pm

Well, I would think it would be, but connecting negative to ground isn't going to make the transformer / battery too happy...<p>So, I don't think so.<p>-Mike

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Re: Circuit Common?

Post by dyarker » Tue Dec 30, 2003 7:44 pm

You could say that. But common isn't neccessarily ground strickly speaking. Portable battery operated gadgits typically aren't connected to ground at all. But in lingo the common is often called ground.<p>Hope I haven't confused you worse.<p>Cheers,<p>[ December 30, 2003: Message edited by: Dale Y ]</p>
Dale Y

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Re: Circuit Common?

Post by dyarker » Tue Dec 30, 2003 8:14 pm

Mike - please stop.<p>Zeek - Follow the instructions. Common is often called ground, like I said. Whether common is actually connected to ground depends on the circuit. In some medical equipment definately NO, PCs have common connected to chassis to green wire ground at one point to reduce RFI. Battery operated stuff in plastic boxes don't need ground at all, home built radios generally play better if common is grounded. If you run 110 VAC to a metal box or box with exposed metal, the metal must be grounded for safety. Whether common is also connected to ground depends on isolation and circuit operation. It depends.<p>A battery or wall wart transformer does not care if one polarity is grounded.<p>Cheers,
Dale Y

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Re: Circuit Common?

Post by samsmiles » Tue Dec 30, 2003 9:19 pm

Hi Zeek,
Circuit common can be ground in terms of ground ground (such as the one on some prof. power supplies; battiers are not conncted to it and neither are wall warts).<p>Circuit common is just like a level in appartment building which you call common or start counting ground it can be something what's 3 floors above the ground but as long as everyone in attached appartment buldings knows where you count from everyone will know where to find you, like a reference.<p>Old type ground meaning 0 Volts is hardly ever needed in our circuits but then again you might have a circuit that might need it so make sure you check it. Circuits needing it are ones that need grounding(medical applications etc). I'm sure its specified in your application notes if you need it.<p>Hope this helps. I had same thoughts when I started with this electronics hobby some time ago ie was confused but folks here explained it to me and I read a bit and I guess I get it now ;-)
Good Luck, Sam<p>[ December 30, 2003: Message edited by: Sam Smiles ]</p>

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Re: Circuit Common?

Post by dacflyer » Wed Dec 31, 2003 4:52 am

Dale said DEPENDS..heehee<p>
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Joseph
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Re: Circuit Common?

Post by Joseph » Wed Dec 31, 2003 11:33 am

Well, curious, I did a little internet research and did not find the term. However here's my definition of circuit common: a voltage potential to where a set of electronic circuit paths return either electron or "hole" current. A "hole" is the positive potential following an electron as it moves through a conductive medium.<p>If anyone detects a flaw in my defination or has found one in a good reference source of electronics knowledge, feel free to comment.<p>[ December 31, 2003: Message edited by: Joseph ]</p>

Sparky Williams
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Re: Circuit Common?

Post by Sparky Williams » Thu Jan 01, 2004 1:11 am

Thanks guys for your input. To clarify things I think I should supply some more information on the circuit I'm planning to build: <p>The project is a wireless remote control gadget, consisting of a transmitter and a receiver. The receiver circuit calls for a 12 volt AC source. However, the article says the unit can be powered with a 12 battery instead -- which is what I want to do. <p>The instructions state, in part, as follows: " If it is desired to power the receiver from a 12 volt DC source, it may be done so by using the same PC pads as for AC, without regard to polarity. Alternatively, the diode bridge may be deleted from the circuit and the positive lead of the DC power source connected to the positive side of C3. The negative side of the supply would then be connected to circuit common." <p>Since I am a beginner at this hobby and am trying to learn, I went out and bought a solderless modular breadboard at Radio Shack and plan to build the circuit on it. I also intend, as suggested by the instructions, to omit the diode bridge. <p>My questionis this: Can I just dedicate a column in the breadboard as a ground or a "circuit common" and have all ground connections going to it?<p>Thanks.<p>Zeek

Sparky Williams
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Re: Circuit Common?

Post by Sparky Williams » Thu Jan 01, 2004 1:16 am

I forgot to mention -- for what it's worth -- this article appeared in Nuts & Volts (April, 2002). <p>Zeek

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Re: Circuit Common?

Post by bodgy » Thu Jan 01, 2004 2:48 am

In this particular circuit common as others have said, is just the return or negative rail for this circuit.<p>If you leave the bridge rectifier in place, and connect the battery to the AC inputs, you have what can be termed a bi-directional poer input, meaning that it actually won't matter which way around the battery is as there will always be two diodes of the correct polarity allowing the circuit to be correctly powered. However the power to the circuit will be approximately 0.6 to 1.2 volts less than your battery voltage. Removing the bridge rectifier, will allow the full battery voltage to be seen by the circuit, BUT the polarity of the battery connection will now be important.<p>Some designs will have bridge rectifiers as a way of 'idiot proofing' power connections.<p>Note that what I've said applies to the above DC powered circuit.<p>If you research Full Wave Rectifiers or Bridge Rectifiers (same thing in this context) you will see why the input can accept an AC or DC voltage.<p>Colin
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Re: Circuit Common?

Post by bridgen » Thu Jan 01, 2004 7:32 am

I shall borrow and modify the first few words from the best selling book in the world, "In the beginning God created the heaven and the earth", viz. "In the beginning there was Earth". <p>When the telegraph was invented they strung up just one wire on poles. Instead of using two wires they connected the other side of the circuit to the planet on which we all live - Earth. <p>It doesn't/didn't matter which polarity of the circuit, pos or neg, was connected to the wire and which to earth. The Earth was used simply as another conductor. <p>And then came radio, or wireless as it was known.
The radio was connected to the antenna system by two connections. One to a long wire, the other to Earth - which was an important part of the antenna system. <p>With the advent of mains power and the use of metal for the chassis upon which the radio was built, the chassis was also connected to Earth for safety reasons. <p>If you look at the circuit diagram (schematic) of an old radio you will see that the chassis not only has the connection which goes to the Earth but also has a lot more things connected to it. One side of the tuning components, cathode bias resistors and their by-pass capacitors and the negative side of the h.t. supply. It could also have, in battery powered receivers, a connection to the positive side of the grid-bias bettery. <p>This/these connections got to be called circuit common. It was a connection common to many parts of the radio.<p>Just like in your city. You may have a street called Main Street many miles long which passes from one side of the city to the other. Along its route there will be several communities or barrios all with different names. Main Street is common to all of them.<p>In a tube radio the h.t. supply is also common to all the stages, but you can see that you would be well advanced on your path to stupidity if you started calling that "circuit common" too! <p>Moving forward towards the present and battery operated equipment. We still call the negative side of the supply the "common" - although when most, if not all, of the available transistors were pnp I suppose we used to think of the positive side (drawn at the bottom of the circuit) as the common. <p>You may know that some (mains powered) equipment has two or more power supply rails of different voltage and polarity. Possibly +24 +12 +5 -12. The other sides of those, i.e. the neg sides of the 24, 12, and 5, and the pos side of the other 12 will all be connected together and circuit "common". So the common in this case will be the negative pole of the 24V supply, one of the 12V supplies, the 5V supply and it will be the posistive pole of the other 12V supply. <p>If this proves troublesome for you to think about, metally replace the supplies with batteries and try again. <p>Somewhere, sometime, someone started to call the common connection/s "ground", which presumably was a euphemism for "earth". <p>Well Mister, not on my pocket radio it ain't! I can assure you that there's no connection to earth dangling from my pocket. <p>We have the unfortunate situation where people talk about "earth ground" and "chassis ground". You can see from this thread, and many which have gone before it on this and other forums what confusion has been caused. <p>This is simply because people misuse words which they don't properly understand because they think it's smart. It is prevalent with technical terms in particular and the English language in general. The lay press, and often the "specialist" press are both guilty. <p> <p>I have a voltmeter with a video amplifier in it.<p>A WHAT? A video amplifier. To most people the first thing that comes into their head will be the familiar offshoot of television.<p>Video amplifiers were in use long before television was invented.<p>Video = wide band.<p>See what I mean?

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