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PCB layout

Old-school PCB tracking method is notebook sheet with cells. Prefer sheets with cells matching to cells on another side, if you use this one. This makes two-sided PCB trackings look clearer. Tracks and parts are drawn at 2:1 scale.

New-school solution is CAD software. This type of software can be even not intended for PCB tracking, or even simple vector editor like Inkscape. But, best results give special software, such as EagleCAD or Sprint layout. Unfortunately, there is no way to find universal software for all, some features considered as useful for one will bore another, and the only way is experiments. Download trial version, test it and uninstall, if you don't like it. Tracking process begins from parts placement. Place big thing (LCD screen, for example) first, and then add smaller parts. You're not need to place all parts as closer as possible, leave some space to make PCB looks clearer. This also ensures better ventilation of power parts. Devices for ordinary usage does not require to be small. Wide PCB is also easier to debug.

If one or few wires does not tracing without intersections, you can alter parts placement. Alternatively, ypu can install some jumpers on other side of PCB. The tracks can also be on other side, even if there are no more than 15 of them. If less, try to make connections with jumpers, avoiding parts placement on other side. Try to avoid pads on both sides at transistors, ICs terminals and any other things that have more than two terminals. In case of failure, these pads make component unmounting more difficult. Good practice is making jumping pads (on both sides, intended for track transition to other side) a bit greater of dimensions than other pads.

Transistors, relays, ICs are easier to mount when placed in one direction, e. g. first terminal to left.

Digital circuits require small (0.1-1 uF) ceramic capacitor connected to power terminals of each IC and module, and medium (100-1000 uF) electrolytic capacitor connected to power terminals of whole circuit. If there are mutiple power supplies, there also should be multiple capacitors. Power supply voltage should stay within 30% of capacitiors maximum voltage, i. e. use 63 V cap for 24 V supply. Greater margin is better, but do not use extremely high volage electrolytic capacitors (i. e. 400 V cap for 3.3 V supply), because of their worse current leaking parameters. With AC power grid supplies these capacitors increase total circuit load, with battery power they are result in shorter battery life.

Tracking examining is commonly searching for unconnected tracks or component terminals. These ones usually are places if the errors.


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