How to Read Schematics?

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Sparky Williams
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How to Read Schematics?

Post by Sparky Williams » Tue Nov 25, 2003 2:53 am

I'm trying to learn about electronics and have a project in mind that I read about in a magazine. The problem for me at this early stage of the educational process is that I can't read schematics. I've learned many of the various symbols for components, but I can't understand how to actually connect components from the schematic diagrams. Can anyone advise me how I can go about learning to read them? Any recommendations on some good books or articles on the subject? Thanks.

cato
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Re: How to Read Schematics?

Post by cato » Tue Nov 25, 2003 3:50 am

Sometimes schematics in magazines are general in nature and do not contain enough information, by themselves, to acutally build the circuit. Instead they show the general ideas of a circuit...and amplifier here, a filter goes there, some feedback between these two points. I'm guessing that you are refering to these kinds of schematics.<p>A more detailed schematic, or a schematic in combination with a Bill of Material or Parts List would specify each component (which kind of amplifier or transistor, what value and wattage resistor. what value capacitor, etc) and specify pin numbers and everything else you need to build the circuit. The exception to that is, sometimes, even detailed schematics don't show some power and ground connections. It is assumed that you know how to make those connections or can find out by looking at data sheets for the parts in question. They are left off the schematic either to reduce clutter and make the schematic easier to read, or out of laziness.....take your pick.<p>If you are refering to these more detailed schematics, then please be more specific about what you don't understand.<p>In general, the answer to your question is the same as the answer to :How do I learn how to read. First learn the alphabet, then try to read and keep trying until the light comes on. It sounds like you have already started learning the alphabet and are trying to read....keep it up, you'll get there.<p>[ November 25, 2003: Message edited by: cato ]</p>

Lin Farquhar
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Re: How to Read Schematics?

Post by Lin Farquhar » Tue Nov 25, 2003 5:34 am

Don't get sucked into linear electronics, it's cheaper to buy an amp or filter (or whatever).
Amplifier design is not a science, it's a black art.<p>Digital - go for it!<p>There are 10 kinds of people, those who understand binary and those who don't.

Bernius1
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Re: How to Read Schematics?

Post by Bernius1 » Tue Nov 25, 2003 10:09 am

I got the same torment from textbooks. Everyone knows the basic NPN amplifier ( funny, I typed 'amplifire' first. How many of THOSE have been built?) circuit. Q1, Rc, Rb1 & Rb2, Re, & coupling & bypass cap's. But WHAT VALUES ?!?!?!
A) Set voltage source (say 12V)
B) Open Digi-key/Mouser/Radio Schlock/Future-Active catalog, & READ transistor spec's. Stay within them.
C)DO THE MATH regarding current/voltage in each leg of the circuit.
D) Choose component values to set those values ( Ohm's law - E=IR)
They don't always TELL you that Signal power is entirely different from DC/Quescient (in books),and like things.
What I'm telling you is that most 'generic' circuits are drawn that way to show a principle of operation which you can tailor to your own liking, with your own values. If you have an actual circuit to build, look for pinouts of the listed devices. Chipdir.com , google, Natsemi, or ONSEMI.
Can't we end all posts with a comical quip?

Sparky Williams
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Re: How to Read Schematics?

Post by Sparky Williams » Tue Nov 25, 2003 1:28 pm

Cato,<p>Thanks for your reply. I am referring to detailed schematics. In fact the project I have in mind appeared in the April, 2002 issue of Nuts and Bolts (Building a remote control transmitter and receiver to power appliances such as a lamp, radio, etc.). The article contains a parts list supplying the specifications for the parts, together with parts numbers, etc. <p>What I don't understand is how to put the parts together from looking at the schematics. For example, the schematic, like most schematics, shows intersecting lines running from various components (I doubt very much that the actual wiring of a circuit entails connecting intersections). Some intersections have dots in them and some don't. Do lines in a schematic illustrate the copper lines that appear on a printed circuit board? I believe - and I could be wrong - that intersecting lines with dots in them mean that the two are meant to be soldered together, and the intersections without dots in them are not meant to be soldered together. <p>Another question has to do with ground. Many schematics show ground symbols throughout a diagram. How do I ground these various items?

Bernius1
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Re: How to Read Schematics?

Post by Bernius1 » Tue Nov 25, 2003 1:41 pm

You're right. Dots mean they connect. But the length of line between components and that dot may differ on the PC board. From one dot, lines may go all around the schematic, but on the PC you'll see a 1/4" oval with four holes where the leads get soldered. Look at some old junk PC boards. You'll see a large area of copper, usually with a line running the perimeter. This is usually GND, so pieces anywhere can connect. BUT !!! If your design is RF, NO closed loops, NO long lead protrusions, NO long lengths of parallel copper which carry interfering signals. If you can use Surface Mount Devices (SMD's), all the better.
Can't we end all posts with a comical quip?

hlreed
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Re: How to Read Schematics?

Post by hlreed » Tue Nov 25, 2003 1:54 pm

Zeek, understand that schematic and pcboard layout are different views of the same subject.
In order to build from a schematic, you must lay out a board that you can them plug your components into and solder them. Nothing can be made from a schematic except a pc board.
You can also use sockets and wire the pins together directly. For a one time project, that might be best.
Harold L. Reed
Microbes got brains

cato
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Re: How to Read Schematics?

Post by cato » Tue Nov 25, 2003 4:56 pm

Zeek -
Like the other guys said, dots mean connection, no dot means the guy who drew the schematic didn't see a way to draw the line from point A to point B without crossing the other lines. There is no electrical significants to the route a wire or line takes in a schematic. In fact, sometimes 4 op amps or 4 nand gates come in one package. Even so, the four devices may be drawn on 4 corners of the schematic or even on different pages of the the schematic. The schematic shows whats connected to what. It does not show where the components go on a circuit board.<p>The first rule in building a device from a schematic is connect all the pins together that are shown connected together.<p>After that comes defensive lay out. In order to avoid noise, ground loops and other stuff thats hard to track down and fix after the fact, try to mount parts that are connected together close to each other. You dont want to run wires or circuit board traces for a feedback resistor in an op amp circuit all the way across the board. They can act like antennas and pick up unwanted signals.<p>As far as ground is concerned, try to place grounded components close together so that they can be connected with short lenghts of wire (I use green)or copper traces. Failing that, connect grounded points back to a single point. This is called a star ground. The extream alternative is a daisy chain. Since wires are not acutally zero ohms, the current flowing to ground from a device at one end of the chain can raise the voltage on ground as seen by other devices. This is to be avoided, which is why the star ground is recommended. The best thing to do is use a multi-layer circuit board and have an entire plane or layer for ground. Similar recommendations apply to the power supply.<p>How are you planing to build the project? With a printed circuit board or point to point wiring? Do you know about "perf board"? It comes in sheets and has a grid of small holes in it. Generally you place components (or sockets for components) on one side and the leads go through the holes. You do your wiring between the pins on the other side.<p>I'm sure the other guys will have other tips. I think the only real way to learn is to try.

russlk
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Re: How to Read Schematics?

Post by russlk » Tue Nov 25, 2003 5:39 pm

I think the best route for a beginner is to use perf board and wire the parts. In many cases the leads of the components can be used, and where an IC is to be wired, #30 Krynar is easy to handle. The beginner will probably learn the hard way that power connections to a common point is better than daisy chain connections. The first thing for a beginner to learn is how to solder: heat the joint until the solder flows and clings to the wires.

Sparky Williams
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Re: How to Read Schematics?

Post by Sparky Williams » Wed Nov 26, 2003 4:02 am

No_Vice,<p>What are "pinouts"? Also, I've seen schematics where a line goes from a component to a ground in the middle of the diagram (in addition to other grounds in the diagram). Do I just have a single blob of copper (whatever that is called) for that one ground -- sort of like an island of copper? And, when you say "no closed loops" what exactly do you mean?

Sparky Williams
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Re: How to Read Schematics?

Post by Sparky Williams » Wed Nov 26, 2003 4:11 am

Harold,<p>I'm not sure what you mean when you say I must "lay out" a board. How do I get a board containing all the lines of copper that tract the schematic? Do I get a blank board with all copper on one side and then cut out the copper I don't need, leaving the lines of copper I do need?

Sparky Williams
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Re: How to Read Schematics?

Post by Sparky Williams » Wed Nov 26, 2003 4:27 am

Cato,<p>It sounds to me from what you and Russ Kincaid said that I should start with a perf board. When you say "wiring between the pins," I take "pins" to mean the leads from a component.

Bernius1
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Re: How to Read Schematics?

Post by Bernius1 » Wed Nov 26, 2003 4:55 am

Zeek, Icouldn't effectively paste an image here. But go toGoogly eyes on you, click on the 'IMAGES'tab, & type the part number of a component on the schematic. Or start with an easy sample, like LM324 , or LM358, or CD4011, or LM555. They all show something. Or just look for '.PDF' Adobe pages on the regular search. You'll see the pinout as a rectangle with the schematic images inside it, and Vcc (+) and GND pins. On the PC board, the GND pin gets a copperlead to the big island along the side. 'No closed loops' means; From one chip to the next, maybe from the VCO ( Voltage Controlled Oscillator) output pin to the input of the power amp, the copper strip may make a giant 'C' shaped path around other components. This may act as an antenna, radiating to other devices on the board causing noise & feedback. And if copper traces on opposite sides of the board carrying signal are parallel, they can suffer inductive or capacitive interference.
For prototypes, the Radio Shack has 2x2 boards pre-drilled with a DIP layout in the middle, and + and GND strips along the side. You jump from land to land with component legs, and jumper-wire the rest. But at RF, the noise may be excessive.
Buy a breadboard. $20.00 of instant pleasure.
Can't we end all posts with a comical quip?

Sparky Williams
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Re: How to Read Schematics?

Post by Sparky Williams » Wed Nov 26, 2003 11:58 am

no_vice<p>So, if I see a schematic showing several instances where a line goes from a component to a ground, thus showing several grounds that look isolated from each other in the schematic, in reality all these isolated looking grounds in the schematic are connected by copper running along, say the side of the PC board?

Sparky Williams
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Re: How to Read Schematics?

Post by Sparky Williams » Fri Nov 28, 2003 12:57 pm

To Everyone,<p>I want to thank all you fellas for giving a neophyte like me your time and very helpful comments. <p>Zeek

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