Search options (Page 3 of 3)

› Circuitry Crash-Course

‹ Circuitry Crash-Course

A schematic is a document that maps out a circuit like a blueprint maps out a building. Unlike a blueprint, the physical location and size of the components in a schematic do not reflect what ends up on a printed circuit board (PCB). The schematics I’ve designed above have red components, and blue connections between them.
There are a few different ways to communicate what connects to what, but the way I’ve chosen is (in my opinion) easiest for a novice to understand, even if it seems busy. The blue connections represent an electrical connection between components; sometime multiple components. But, again, because the locations of components on the schematic have nothing to do with the physical location on a PCB, this may be deceiving at first.
Sometimes the blue paths cross over each other, but this doesn’t mean the pats are connected. If there is a circular dot at the interception they are connected, otherwise they do not. It would be best if there were no crossing over at all, but this is almost never possible when drawing more complex circuits in the style I’ve chosen to use.
All components have a name. These names are always a letter or two followed by a number. Every component name on a schematic is unique. The letter(s) at the start of a name indicate what type of component it is, and the number differentiates similar components. There are different schools-of-thought when it comes to these abbreviations, but typically resisters are R, diodes are D, capacitors are C, integrated circuits are IC, and so on. If you’re not sure what these components are, I have a short index with simple explanations and links for further reading. The Gameboy schematic doesn’t always follow the standard abbreviations, instead I chose to use the names assigned by Nintendo to prevent confusion in that schematic.
Along with names, components typically have an assigned value. These values aren’t necessarily unique, but they indicate which specific type of component it is. Sometimes, for specialized components, it’s a jumble of numbers and letters indicating a model number, though more frequently they give a unit value. For instance, resistors are measured in ohms, capacitors in farads, and so on (you don’t need to learn these terms). Frequently the unit is omitted to keep from cluttering up the schematic. But sometimes letters are needed, that’s why you see things like K for values multiple of 1000, and µf for microfarad.
Some red symbols on the schematic aren’t components, most notably VCC and GND. I try to explain what these are in the index below. These are the one time I take a shortcut (otherwise things would get really cluttered). Everything labeled either VCC or GND are connected somehow; the connection does not just end, but it doesn’t go into a component.
There’s another symbol that I use (it looks like a C with a line coming out the back) to represent an off-board connection of some sort. Sometimes it’s a socket or jack, other times it’s just a hole on the board a wire is soldered to. Regardless of what it is physically, it’s a point on the schematic that the circuit is physically leaving/entering the circuit to/from something off the board. At the end adjacent to the connection there is a label indicating where exactly that part of the circuit is going
The last thing I’d like to mention is about integrated circuits. These are represented by large rectangles with short lines coming out of the left and right sides. Each one of those lines represents a physical contact on that particular ‘chip’, called a pin. Each pin has 2 associated labels. One is the pin number as it is counted on the physical chip, and the other is how that pin is used by the integrated circuit. On the schematic, these pins are almost never ordered sequentially, but are typically grouped by ‘type’ of pin. The purpose for this is to make it easier to group connections going to and from similar locations, because the schematic is meant to show the logical organization of the circuit, not the physical organization.
There’s plenty of online literature and YouTube videos to help you learn much more than what I’ve written, but hopefully I’ve given you enough to start with, and preemptively answered any questions you might have about how I’ve drawn these circuits.

› Component-Type Index

‹ Component-Type Index

• Amplifier
  Amplifiers are a 'chip' that boosts signal strength. Frequently used to boost audio, like how it’s being used here. The left and right channels of audio produced by the CPU is really, really quiet. That signal (which is analogue) is boosted, or amplified, to a level it can be easily heard through headphones or the front speaker. There is only one front speaker, so the audio sent from the amplifier to the speaker is the summed left and right audio. This is also called mono.

• Capacitor
  Capacitors are storage. They can hold a reserve of power or store any excess energy, but have a limited capacity. They help smooth over the highs and lows of a signal. Unlike other electrical components, they do not connect the circuit at the points they’re soldered. They use the difference in ‘pressure’ between the two sides they’re soldered to store or release energy as needed.

• Capacitor (Electrolytic)
  Electrolytic capacitors are a type of capacitor that have a much larger storage capacity for one of its solder points. That’s why it’s important to have them installed correctly, and not backwards. That’s why electrolytic capacitors are typically larger and always have a mark or stripe indicating the way it should be installed.

• Central Processing Unit
  this is the main number cruncher ‘chip’ for the circuit. There may be other ‘auxiliary’ processors, but the one at the heart of the circuit is called the ‘central’ one. It’s sometimes called the ‘brain’ of the circuit.

• Diode
  Diodes are components that allow current to flow in one direction and not another. A one-way street for the circuit.

• Diode array
  An array is simply multiple ‘things’ put together in some organized manor. A diode array is a single component that has multiple diodes. The one used on the Gameboy has two diodes that are connected in the same direction. If a diode is a one-way street, the one used here is a one-way street with an intersection in the middle of it.

• Ground
  Ground is the word used for the ‘minus’ end of the battery. To keep things from getting confusing, think of it as the end destination for power in the circuit.
  Plug/contact/socket/port
  these are terms used for various ways where an electrical connection is made in a non-permanent way.

• Potentiometer
  this is a type of resistor where the resistance can be varied manually. These are used to control the volume of the audio and contrast of the screen.

• Random Access Memory
  This is a ‘chip’ that works with a processer to keep track of data. The data it stores is really, really basic. Once the power has been drained from the memory, it’s gone for good.

• Resistor
  this is a component that makes it difficult for current to pass through. These are frequently used as passable ‘road-blocks’ to ‘slow-down’ the current, or ‘motivate’ it to go elsewhere.

• VCC
  Fancy acronym invented by electrical engineers to keep things confusing as a way of job-security. Without explaining what it means or why it’s called that, just think of it as the source of power, or the ‘plus’ side of a battery.

› Archived Conversations

‹ Archived Conversations

Yeah, I saw that. I wanted something that was more of a 'wtf am I looking at' guide. Because, when I started, that was the question I was asking myself.

No kidding. I was looking for any documentation for the LR35902 CPU or the LH5264. Through-hole components are easy enough to guess. But if anyone is holding out, I'd love to see any spec-sheet for them. The component library I made for this was based almost entirely off the scan (there's sort of a way to make a raster image in eagle), but I know I'm fudging it a bit more than I'd like.

As I was compiling the images you see above I had one of those 'what I should have done was...' moments. I'll revisit it when I update the library. So, yes and no.

Ok, so let me pick your brain for a moment. How on earth do you make oblong through-holes? I'm doing unspeakable things with layers to get the battery contact points, DC jack, switch, and link port to look right. Part of my reluctance of releasing the file is that whole 'there has to be a better way to do this' thought.

Yes. I've started expanding my custom part library to include the bits on it. But (1) I want to revisit/fix the Eagle-hacks/mistakes I've made before I continue using that library. And, (2) I'm not sure how to tackle removing the screen safely. This is a fully functional Gameboy, and I have no reason to think I've destroyed anything so far (aside from that one cap), so I'm hesitant to try.