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Old 27th April 2011, 04:55 PM   #1
Havoxx is offline Havoxx  United States
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Default Help with reading a schematic

Hey all, I'm having a bit of trouble reading some symbols in some of my schematics I have, I know they are resistors, because they use the R symbol, and the squiggly line(only thing I can think to call it), but instead of having ratings, they have a single number, like 1, or 2, or a letter, such as L, I can't figure out what those mean? There is one schematic, where it seems the numbers are just to tell you there's 5 resistors, is that what the 1-5 would be? and 1m, would be 1milliohm? I'm trying my best to learn all this stuff, and considering I've only been doing it for a week I think I'm doing ok


Also, where's the best online site to get resistors, and capacitors from?
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Old 27th April 2011, 05:31 PM   #2
DF96 is offline DF96  England
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It is normal on a schematic to name each component. So resistors are named R1, R2 etc. They have no meaning other than simply being a label for each component. The value and other parameters may be on the schematic too or in a separate list.

1m would be 1milliohm if it is a resistor, but it could be someone who does not understand SI units trying to specify 1 megohm which is 1M.
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Old 27th April 2011, 06:25 PM   #3
Mooly is offline Mooly  United Kingdom
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Can you post an example showing these resistors on the circuit...
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Old 27th April 2011, 06:28 PM   #4
Havoxx is offline Havoxx  United States
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Well the M, is in uppercase and it's a NS schematic, I can't make it write out properly on the PC, but the RL, is an R with a smaller uppercase L to the bottom right of it, it's on the fifth page of this data sheet, under the bass boost schematic http://www.national.com/ds/LM/LM386.pdf it's towards the end of the output signal

The M is in this one http://www.national.com/ds/LM/LM1875.pdf right on the first page



p.s. nice avatar mooly
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Old 27th April 2011, 06:35 PM   #5
Mooly is offline Mooly  United Kingdom
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Thanks

RL is the load... speaker etc
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Old 27th April 2011, 06:36 PM   #6
Mooly is offline Mooly  United Kingdom
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And that 1M is 1 meg ohm (1,000,000 ohms)
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Old 27th April 2011, 06:41 PM   #7
Havoxx is offline Havoxx  United States
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Alright, thank you so that would mean it needs a resistor in the ground wire of the speaker?

I also had something that I'm pretty sure about, but I do want to clarify, when the resistors/caps are just connected to it like _____._____ is that pretty much just put whatever it says to connect to it there, and then ground it(if it says to ground it), like that bass boost circuit? Where it has em going off into space, I've been teaching myself this, so it's a bit difficult to know how exactly something is, and the book I have just says it means it's connected.
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Old 27th April 2011, 07:01 PM   #8
Mooly is offline Mooly  United Kingdom
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There's no resistor added to RL which is just the speaker itself.

The grounds have to be connected so as to avoid instability and oscillation. That really means using a "star" as shown... bit of a grotty drawing lol
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Old 27th April 2011, 07:04 PM   #9
DF96 is offline DF96  England
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I think the resistor is the speaker, not part of the connection to the speaker. As Mooly says, RL is the normal name given to the load resistance - the thing the circuit is supposed to drive.

Most circuits put a small blob where wires are to be joined. This is unnecessary where only three wires meet, but it is one way to resolve an ambiguity when four wires meet or two wires cross. The modern method is to put a blob if they join, and leave plain if they cross without touching. The old method, which you may sometimes see especially on hand drawn circuits, is to leave plain if they join and put a little half-loop if they don't touch.

As you have now discovered, in electronics there is a difference between 'm' and 'M'. There is also a difference between 'k' (kilo) and 'K' (degrees Kelvin), and 's' (seconds - time) and 'S' (siemens - conductance). Lots of people get these wrong, but it is best if you decide to be pedantic about units as that will help later on when you start to think about calculations.
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Old 27th April 2011, 07:08 PM   #10
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The R with small uppercase L is a generic symbol for the circuit load. Hardly ever really a resistor, it will be a speaker or headphones, LED or bulb, a motor, etc. or maybe even another circuit. A dot means a connection of two or more wires or components. Ground is the 3 tapered horizontal lines.
"Going off into space"? I'm not sure what you mean. In that bass boost circuit, at the bypass capacitor, the dashed lines just mean that it's an optional component.
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