A layout diagram (pattern diagram) is a drawing of where to insert each part on a perfboard and which holes to connect. A schematic shows "what connects to what", while a layout diagram shows "which holes on the board things go in". If you can read one, you can build someone else's layout exactly, and check your own. The most confusing part is the left-right mirroring between the component side and the copper side, so this article goes through it step by step.
Schematic vs. layout diagram
| Item | Schematic | Layout diagram |
|---|---|---|
| What it shows | Connections between parts | Actual positions and wiring paths on the board |
| Part shapes | Symbols (rectangles, zigzags, triangles) | Real part bodies and lead positions |
| Meaning of lines | Electrical connections | Solder and jumper paths, down to length and direction |
| Used for | Understanding and designing circuits | Building and inspecting boards |
Even for the same circuit, a layout diagram can be drawn in countless ways depending on part placement. A good layout diagram has short wiring, few crossings, and tidy power and ground.
Why are the component side and copper side mirrored?
On a perfboard you insert parts from one side (the component side) and solder on the other side (the copper side). If you flip the board like a sheet of paper, left becomes right. So even for the same part, a lead on the left seen from the component side shows up on the right on the copper side.
A layout diagram is usually drawn from one of the two sides.
- Component-side reference: the view you have when inserting the parts. Good for checking part placement.
- Copper-side reference: the view you have when soldering. Good for checking the wiring and the holes to solder.
Always check which side a drawing is based on. If you read it the wrong way round without knowing, the IC ends up backwards or the wires connect mirrored left and right. In the Patterndo editor you can flip the view in one go with the [Component side]/[Copper side] button or the <kbd>F</kbd> key.
Reading coordinates
To tell someone a hole position in words, you need coordinates. In general, a number (column) is used horizontally and a letter (row) vertically, called something like "C12". Which side the numbering starts from differs between drawings.
- The Patterndo editor calls columns by number (1, 2, 3…) and rows by letter (A, B, C…), and the top line (the VCC rail) is row A. On the component side, column 1 is on the left; on the copper side, which is mirrored left to right, column 1 is on the right.
- Paper drawings usually mark 1 and A at the corners. Always read by that marking.
Reading IC pin numbers
A DIP-style IC has a half-circle notch at one end and sometimes a small dot nearby. With the notch at the top, looking down from the component side, the upper-left pin is pin 1 and the numbers increase counterclockwise. With the notch on the left, the lower left is pin 1.
On the copper side the same IC appears flipped left to right, so pin 1 shows up at the lower right (with the notch on the left), and the numbers seem to increase clockwise. This is the cause of the most common mistake. The detailed rules are covered in Reading DIP IC Pin Numbers and Using IC Sockets.
Parts with polarity
- LED: the long lead is the anode (+) and the short lead is the cathode (−). If one side of the body is flat, that side is the cathode.
- Electrolytic capacitor: the side with the white (or silver) stripe on the body is −.
- Diode: the side with the band on the body is the cathode (K).
- Transistor: with the flat face toward you and the leads pointing down, the pin order differs between parts (see the transistor switch guide).
The order to read a layout diagram
- Check the reference side: whether it is the component side or the copper side, and which way the columns are numbered.
- Find the power rails: first look for thick lines in colors like red (+V) and blue (GND).
- IC positions and orientation: mark the IC notch and the position of pin 1.
- Passive components: check the values and polarity of resistors, capacitors, and LEDs.
- Signal wiring: check one wire at a time, confirming its start and end points.
Habits that reduce mistakes
- Right before soldering, flip the drawing over once more and check the part orientation.
- Each time you finish a wire, draw a line over it on the layout with a colored pencil to mark it as checked.
- In the Patterndo editor you can check the diagnostics panel each time you finish a wire. See Reading Diagnostics Messages.
Summary
A layout diagram shows actual positions on the board, and the component side and copper side are mirrored left to right. If you first check which side it is based on, which way the columns are numbered, and where the IC notch and pin 1 are, you can prevent most reading mistakes. The process of turning a schematic into a layout continues in Moving a Schematic onto Perfboard in 7 Steps.